Beginners version
Before beginning the study of the BOP, it is
necessary to understand the rudiments of offshore
petroleum drilling. This is why I tried to make a
summary of it in order to more precisely define the
terms used in the continuation.
Oil results mainly from organic matter trapped in
geological layers and subjected to strong pressures
and temperatures, a weak concentration of oxygen
and hydrogen sulphide. Geology makes it possible
to locate the layers likely to contain some by
exploration drilling will then make it possible to
confirm the forecasts and to determine profitability
of it. It will be followed by drillings of exploitation
which will make it possible to extract the resources
from them.
When one drills through geological layers, one
meets there all kinds of materials of variable
hardness but also fluids and gases. The problem of
drilling mainly consists in using tools adapted to the
ground, to maintain the layers so that they do not
break down but also to control the fluids and the
gases which can endanger the life of the people and
compromise the use of the resources in the event of
explosion or the arrival of toxic gas. The choice of
the tool named "drill bit" is determined by the
nature of the geological layers met. That can be
done starting from the posterior geological analyses
but also by analysis of the spoil gone up by mud
(the "Cuttings") or by observing advance in the
layer which can also characterize its wear. In order
to recover spoil, one uses a drilling mud which is
pumped in the well inside the "drill strings",
injected into the zone of cut by the nozzles of the
drill bit and returned by the annular which is space
between the external part of the drill strings and the well bore.
The density, the pressure of mud and its composition are given
in order to maintain the formation in place and to control the gas
increase in the event of eruption. On the surface, mud is directed
towards units which separate it from the cuttings (shakers,
centrifugal machines...) but also from degasification circuits.
The selection of the way of mud is determined by means of the
"Diverter".
The rotation of the drill bit is ensured by the intermediary of an assembly of "drill strings". This assembly is made up
various types of strings:
− The "Drill Pipes".
− The "Drill Collar", "Heavy Weight" as well as other additional elements.
The "Drill collar" and "Heavy Weight" are in the lower part of the drill string named BHA (Bottom Hole Assembly), the
"Drill Pipe" which are most numerous constitutes the higher part of it. The assembly is calculated so that the centre of
gravity is in the elements the more resistant part of the BHA and to apply a certain force to the tool. In the contrary case,
the drill strings would twist like spaghettis under the bending stresses.
The drill strings are tubes of diameter standardized (F.ex: 5' 1/4 or 3' 1/2) equipped at each end of "Tool joint" of more
significant diameters allowing to screw them between them. The "Tool joints" are directed with the males in bottom and
the female in top during drilling and are tight between them using drilling tong.
For directional drillings, the drill strings are not involved any more in the rotation starting from surface but by bottom
turbines actuated by the mud flow. The principle remains the same one except that the drill strings turn only in the lower
part of the train, after the turbine. This technique makes it possible to be freed from frictions of the well bore on the drill
pipes in the bent parts.
Progressively drilling, we seals and we reinforce the well bore by installing metal assemblies of tubes, the "Casings" or
"Tubings". At sea, first "Casing", the "Conductor pipe" will make it possible to fix the wellhead which will be also the
support of following casings. On the contrary of the "Conductor pipe", other casings will be cemented in the ground and
tested before restarting drilling. Cement is drilled again when the operations of drilling restart. As one proceeds by stages,
these casings are assembled one in another with decreasing diameters with the depth. The subsea BOP who is the
equipment allowing to control the well is fixed on the wellhead using a connector sealed with the pressure named "Well
head connector". This connector must provide to support the efforts generated by the weight of the BOP but also those
caused by the movements of the risers and those depend on the operations.
In deep offshore drilling, the BOP is connected to surface by an assembly of tubes - the "Risers" - which make it possible
to contain mud in the water column. It is in these "Risers" that the drill strings and mud pass. Mud arrives in the well by
the interior of the drill strings and returns on the surface by the annular i.e., between the outside of the drill string and the
risers. Risers are thus to some extent the prolongation of the borehole.
At the time of gas arrival, the control of the well can be carried out on the surface by the "Diverter" or by the BOP at the
seabed. In this case, one closes jaws named "Rams" on the drill strings and one controls the release of gases by adjusting
the flow, the density of mud and by using the lines "Kill & Choke" of the BOP which goes up on the surface on fixed lines
assembled on the risers towards "Choke Manifold". This last is a whole of valves making it possible to redirect the fluids
towards various destinations.
The risers are also used as support for three hydraulic feeders for the BOP, both "Conduit lines" and the "Hot line", two
electric umbilical and the "Booster line" which is used to restart the circulation of mud when it was blocked. We will
detail the whole of these lines in the continuation of the text but without however going into the details of their use during
drilling. You will find in appendix some references allowing you to look further into your knowledge in drilling and
control of well
2. General description of the system.
The system Multiplex or MUX of Cameron has for principal function to control the equipment being used for controlling
or closing a well of drilling according to recommendations of the API (American Petroleum Institute). The API is an
organization which defines applicable recommendations (RP), specifications or standards in the domain of oil drilling.
It is an essential element for the safety of the people and equipment on offshore drilling rigs. A failure of this equipment
can involve disastrous consequences in term of human lives, economy and ecology.
It is about an electro-hydraulic system ordered by programmable automats (PLC for Programmable Logic Controller) and
used in marine environment with depths of water exceeding the 500m. For lower depths of water, the BOPs are entirely
ordered hydraulically by the intermediary of hydraulics umbilical containing a hose for each function. With the depth, the
response times of the orders increase and can pose problems of safety when one wants to control the well. The electric
systems make it possible to be freed as of this time constraint as well as constraints of size of umbilical related to the
number of functions.
In operation, the equipment of control of well - the BOP (Blow Out Preventer) at the sea-bed and the Diverter on the
surface - are controlled via two functionally identical control panels: The TCP (Toolpusher Control Panel) and the DCP
(Driller's Control Panel). The TCP is located in the office of the "Toolpusher" in neutral zone and the DCP conceived to
be able to work in explosive atmosphere is located in the "Driller's Master Cabin" on the drill-floor.
The BOP is equipped with the electronic of command contained in containers called SEM (Subsea Electronic Module).
Each SEM contains two electronics A & B independent in term of communication and power supply.
The "Diverter" can also be controlled by the intermediary of a purely hydraulic panel of the HPU (Hydraulic Power Unit)
or by another being in the "Moon pool" (the central part of the boat giving on the sea and allowing the passage of all the
elements necessary to drilling).
Note: One calls sometimes SEM one of electronics A or B of the SEM. I prefer to preserve the term of electronics A & B
not to add to confusion. It should be noted that there is also a SEM in acoustics of some BOP. In this case, I would specify
"Acoustic SEM".
The SEM are installed in the systems of hydraulic control called POD to which one allots the colours Blue and Yellow
following their position on the BOP. In general, Yellow is on starboard and Blue on port side. The POD are
interchangeable and are numbered from 1 to 3. In this case, there are two operational installed on the BOP and one spare
on the surface. On certain drilling rigs, it can append confusion between the colour of painting of PODs and that allotted
by their position on the BOP. It is thus preferable to preserve the numbers to indicate them rather than colours especially if
the doubt is possible with the Blue and Yellow positions.
The hydraulic power of the whole of the system is provided by the HPU with its own control panel which can function in
explosive atmosphere. Pneumatic pumps supplied by the rig air allow remedying any loss of the power on the electric
pumps. The electric pumps can also be made inoperative if one is obliged to cut the power at the time of gas arrivals or of
a blackout (total loss of power). A set of accumulators on the surface and on the BOP makes it possible to ensure a reserve
of power on the surface and to make buffer when basic functions are activated.
The electric power is provided by two inverters (UPS for Uninterruptible Power Supply) supplied with the generators of
the rig on independent lines. Each inverter has a minimum of 2h of autonomy in normal operation on battery.
The equipment of the subsea BOP communicates with surface and is provided in electric power via two electro-optical
umbilical, one for the POD Blue and the other for the POD Yellow. These lines are not permanent and are rolled up or
unwound depending if we descend or recover the BOP. The optical part is not used in our application to the creation date
of this document but it was supposed to transmit the video signals for cameras or those of another acoustic system
positioning. The majority of the rigs are not equipped with it.
The hydraulic power is provided to the BOP via two permanent hydraulic lines fixed on the risers - the "Conduit lines" - to
which it is necessary to add a line called "Hot line" being used mainly for the reanimation of a POD when the "Stingers"
are in place during the connection or the disconnection of the "Risers" or as a safeguard. The "Hot line" which is optional
on other rigs is not a fixed line and comes from a third reel which is progressively reeled during the descent of the BOPlike for the electrical umbilical.
The whole of the system which is a fundamental element of the safety of a well has levels of redundancy which make it
possible the equipment to function in degraded mode without endangering the well, the people and the environment. Toensure the operation of this equipment, one carries out functional tests in pressure at key periods of the operations and
before the starting of drilling.
Mux general overview.
3. Structure of the BOP.
The BOP which is only the subsea part of the Multiplex system can be broken up into two principal elements: The "Stack"
(because it is about a stacking of equipment) and the "LMRP" (Lower Marine Riser Package, sometimes simply named
LRP). These two parts can be separate (one says to disconnect) and are maintained between them by the "Riser
connector". Retractable systems named "Stack stingers" make it possible to circulating of the fluid of the hydraulic
functions between the two parts while allowing the disconnection. Other mechanical systems, the "Stabs" or "Piston stabs"
make it possible to connect the conduits "Kill" and "Choke" as well as other additional functions between the two parts of
the BOP.
Note: The example which follows is that of the ship "Pride Angola" but other configurations are possible. Generally, two
very similar rigs do not have obviously the same configuration. The configuration is generally defined by the customer
according to operational and technical requirements.
The "Stack" is the lower part of the BOP. It is attached in its lower part to the "Wellhead" by
the intermediary of the connector named "Wellhead Connector". Before connecting the BOP
to the "Wellhead", one installs a special seal called "VX gasket". Usually, this seal is
maintained in place on the BOP by dogs that a function can release. The seal can also be
installed by a ROV directly on the "Wellhead".
Then while going up, the three obturators called "Lower", "Middle" and "Upper pipe rams", the "Shear rams" then the
"Lower annular".
− The "Pipe rams" are kinds of pistons which make it possible to close the hole on a definite diameter of "Drill string"
and only on that there (for example 5 or 3 inches) according to the "Packers" which are installed there. The "Packers"
are resistant elastomer parts reinforced by metal parts. They serve as with dimensions to ensure the sealing at the level
of the drill strings and other to withstand the service pressure of closing. The "Variable rams" make it possible to
close again the hole on drill strings of different predefined diameters. These rams make it possible to make stripping
i.e. to provide to assemble or descend the drill strings between the two "Tool joint" (the larger part of the drill strings)
while maintaining the annular closed and by keeping the sealing. In all the cases, for the closing of the rams, it will be
necessary to position the "Tool Joint" so that it is not in the jaws. The annular is the part located between the well bore
of the hole or casing and the external part of the drill strings where is circulating the return mud
Cameron
DL annular
VETCO
connector
Shear rams
Variable rams
Rams Pipe rams
− The "Shear rams" (or "Shearing Blind rams") is an obturator which make it possible to cut drill strings of a specific
grade (related to hardness of the metal) and to close the well. In this case, mud is controlled only by the lines "Kill"
and "Choke" which go up on the surface.
− All the "Rams" are equipped with a "Lock" or blocking system which makes it possible to keep them closed even
when there is no more fluid of command under pressure. This system is an additional safety which can be used either
under normal operation of the BOP or in the event of urgency. The "Lock" is useful mainly on the "Shear rams"
because it makes it possible to close the well and to disconnect the BOP by leaving it without hydraulic pressure in
the system. The "Lock" can also be useful at the time of a "Hang off". In this case, it makes it possible to rather
maintain the train of drill strings in the BOP than to drop it in the well after the cut by the "Shear rams". The
principle of "Hang off" is to reassemble the train of drill stings so that a "Tool joint" is with the top of the "Rams"
which will be closed. In this case, one will maintain the drill string with the "Tool joint" laid down on the "Rams".
At Cameron, there are two types of system of "Lock". The "Ram lock" and the "St-lock".
Above the stack of "Rams", we find the "Upper annular". It is the last item of the "Stack" before the LMRP:
− The "Lower annular" (and in certain case when it is installed the "Upper annular") is an obturator which can be
closed on any shape of drill strings being able to be in the hole or to close the annular completely when the pressure of
closing is applied. It allows rotation and stripping without taking account of the "Tool joint" of the drill stings. The
closing element is an elastomer reinforced by metal parts included inside. It must support the conditions of
30 L ?
RAM LOCK – NORMAL OPERATION
temperature and the chemical and mechanical aggressions of the medium to the operating pressure. The two annular are sometimes used together to avoid leaks when a "Tool joint" cross one of them.
The "Stack" contains also the 8 valves "Kill" and "Choke" which allow the control of the well, the automatic disconnection
acoustic system and the accumulators.
The "Kill" and "Choke" valves are noted "Outer" when they are towards the outside of the BOP, "Inner" towards the interior of the BOP, "Upper" for the high part and "Lower" for the low part. That's explaining the names LIK (Lower
Inner Kill) or UOK (Upper Outer Kill) for example.
The acoustic system is completely independent of the electric operation of Mux. It requires the deployment of two arms
Figure 10 BOP general overview.
ST-Lock
equipped with transponders allowing the acoustic communication with surface. The assembly is driven by an electronic
container and a hydraulic bloc associated with independent accumulators.
Lastly, all in top of stacking is the male part of the "Riser connector" to which will come to connect the LMRP. The
LMRP is the higher part of the BOP. It is prolonged in its higher part by the "Risers" which connect it with the equipment
of surface. The riser is a hollow tube of 23m (900") length equipped with connectors at each end. Some are naked; others
can be equipped with floats. The unit is assembled in a precise order which makes it possible to limit the compression
efforts at the level of the BOP. The risers equipped with floats are installed on levels which make it possible to
compensate for the weight of the whole in way on the one hand that the "Risers" do not flame and on the other hand that
the weight is not applied in the lower part. This is in order to avoid applying too much effort at the level of the connection of the BOP (flex-joint and riser connector).
Each riser has five permanent lines: 2 lines diameter 1' 7/8 for the "Conduit lines", 2 lines diameter 3' 7/8 for the lines
"Kill" and "Choke" and the "Booster line" of diameter 3' 1/4. The "Conduit lines" are used to feed the BOP in hydraulic
power whereas the lines "Kill" and "Choke" make it possible to control the well or to make circulate mud mainly at the time of the eruptions. The "Booster line" makes it possible to send mud under high pressure when there is a stopper in the
mud circuit.
The first riser, i.e. deepest is connected on the "Flex joint" which is at the top of the LMRP. As its name indicates it, the
"Flex joint" is a flexible joint which allows movements of inclination between the risers which are fixed at the ship and the
BOP which is fixed on the wellhead. According to technology employed, it can be also called "Ball joint". The "Flex
joint" has a maximum angle compared to the vertical. It is also sufficiently robust to withstand the pressures in the well of
drilling. The last riser on the surface is an assembly of risers of small sizes making it possible to adjust the length with the
characteristics necessary for the compensation of the swell by the compensators (Tensionners).
Two inclinometers, one fixed on the moving part of the "Flex joint" and the other on the fixed part of the LMRP in PODs
allow of measurement the differential inclination between the two.
BOP and LMRP details.
STACK
LMRP
Accumulateur
CVM
Rams
RCB
Acoustic
inclinometer
Accumulators
POD
Inclinometer
Flex joint
Kill&Choke
Conduit lines
ROV panel
LMRP
Umbilicals
STACK
Shear ram
Upper pipe ram
Middle pipe ram
Lower pipe ram
ROV panel
BOP transporter
Acoustic arm
This information is permanently controlled by the Operators of the Dynamic Positioning (DPo) of the ship in order not to
exceed the maximum values. The maxima are in general two circles of limit of distance centred on the position of the
wellhead or a maximum angle announced by alarms on the consoles of positioning. Two alarms exist: The Yellow which
indicates that it is necessary to prepare with the disconnection and the Red which imposes the disconnection. According to
the customers, we can also have intermediate zones which are used to prepare the operations to be carried out in the
following zone.
The angles are calculated according to the limits of operation of the various elements concerned. One takes into account:
The height of maximum tide, the maximum length of extension of the sleeve joint and the "Tensionners", the maximum
angle of the "Flex-joint" of the BOPand "Slip-Joint" (UBJI). The "Intermediate Flex-Joint" does not exist in our
configurations. You will find a better description later in the text with drawings.
Below the "Flex joint" we have the annular. The function is the same as the one of the "Stack".
In its low part the LMRP is equipped with the "Riser connector" which is connected on the male part located on the
"Stack". It is a significant element of the BOP of which operation guaranteed the safety of the ship. It is him which by its
opening at the time of an emergency disconnection will make it possible the ship to escape from a dangerous situation. It
can be the case in the event of not controlled eruption or at the time of bad weather when the ship cannot keep its position
and go past the various maximum distances or angles. We will see that there is a particular system named "Anti Recoil"
which makes it possible to control the pull up of the BOP at the time of the disconnections. The functioning is the same as
for the "Wellhead connector" of the "Stack".
Redondances of the system.
The BOP is one of the principal elements of the safety of a drilling rig. This is why certain essential elements of this
equipment have a level of redundancy in order to allow an operation degraded in the event of problem on parts of the
system. We will describe the redundancies of the system without entering initially the general architecture of operation. It
appeared useful to me to detail this part before giving of it a more detailed explanation in the following chapters.
4.1 Concept of "Single point failure".
One calls SPF (Single Point Failure) an element which with itself only being able to make equipment inoperative without
level of redundancy or that procedure cannot give it back in service. One can take into account complete equipment or
each one of its sub equipment independently. A system is regarded as inoperative when it cannot any more provide its
functions normally or if it presents to him even a risk or if it generates a risk which is not acceptable. The definition varies
according to the applications and from the levels of constraints which one wishes.
When there is a level of redundancy and that one of the parts of the systems ensuring the redundancy is failing, one
function is working in degraded mode. One can in this case either always have the whole of the functionalities of the
system or to have only one part of it according to the functions which it is possible to lose while respecting criteria defined
in advance. The criteria taken into account are in general the risks for the persons or material but also for the economy or
ecological.
In the case of the BOP, one must consider several situations: Emergencies and operational situations.
The emergencies require being able to carry out a minimum of functions necessary to put the well in safety. In our case,
that wants to say at least to close the "Shear rams" and some "Pipe rams" or to disconnect the BOP using the "Riser
connector".
Operational operation is more of the contractual side. Under normal operation, the BOP must be able to carry out a certain
number of standard operations. Generally one can tolerate a partial failure of the functions used or complete when they are
not used in the current phase of operation. One can thus tolerate a loss of redundancy not putting in plays the current
operation of the unit. In these cases, one must consider the risks incurred and consequences especially if that affects vital
functions in the event of emergency.
Example 1: The loss of the one of electronic of a SEM implies that the system functions in degraded mode. However it
does not lose any functionality.
Example 2: In the same way when one loses a coil of a solenoid which contains two of them. That functions works but the
redundancy does not exist any more. It is not a question of "Single Point Failure".
In general, one seeks these elements using a study FMEA (Failure Mode and Effect Analysis). This study makes it
possible to cut out a system in subsets and amongst other things to determine the criticality of an element of the system as
well as the effect of the failure on totality or an identified part of the equipment. From these studies one can determine the
points where one must concentrate maintenance or ensure a redundancy. At this level one can perform calculation of
failure rate in order to find out the elements that must be redundant in the system or if they need better reliability only.
See the appendix for more details on the method used. That belongs to the analysis of the risks.
4.2 Electric redundancies.
There are two types of networks: The electric power supply systems and those of communication between equipment.
The circuit of communication between the various panels of surface consists of two independent Profibus fibber optic
networks named A & B. Each link has a fibre of replacement which can be used in the event of defect in place of that of
origin. An introduction to Profibus is in the appendices.
Two networks converge from various cabinets (HPU, TCP, DCP, Event Logger) towards the two units of distribution (DU
or Distribution Unit) A & B (DU A & B) in charge each one with one of the two networks. Each cupboard thus receive the
network coming from two different DU and thus from two different network (in fact the networks A & B). The networks
A & B meet in the cupboards by the intermediary of a RS422 coppers connection. DUs are then connected to electronics
(respectively A & B) of each SEM by the intermediary of the umbilical. Each SEM thus receive the network coming from
two different DU each one in charge of a different network (in fact the networks A & B). The loss of one umbilical
involves the loss of a complete SEM.
The power supply of each cabinet and of the SEM is provided by two UPS so that the loss of the one of the power supply
does not make the system inoperative. Each UPS is fed by independent circuits coming from the generators of the rig. The
feeding circuit follows the same circuit as that of the links of communication. Each UPS feeds one of which distributes the
power supply on the various cabinets and the SEM. Each cabinet thus receive the power supply of two different UPS by
different circuits. Each of both electronic A & B of a SEM is fed by one of the two UPS while passing by the intermediary
of both DU.
For the equipment of surface these two systems offer a redundancy to the level of the data transmission and for the power
supply. On the other hand there is not a redundancy on the level of electronic contained in the various cabinets.
hidraulic on the surface:
The only redundancy at the level of the HPU is that of the pumps. In parallel with the electric pumps, there are
pneumatic pumps supplied with the air of the rig which can take over in the event of electric failure or when one cuts
the power supply following an uncontrolled gas arrival on the surface. This equipment being on the surface does not
require as many levels of redundancy as the basic equipment which must have gone up in surface to be repaired.
There is not always the possibility of isolation of the pumps in the event of problem and this can constitute a critical
point if there are important leaks on one of them.
− Hydraulic Power on the BOP:
The hydraulic power arrives of the HPU by two principal lines, the two "Conduit lines" for PODs Blue and Yellow
and an additional line the "Hot line". The "Conduit lines" are fixed pipes integrated on the risers. The "Hot line" is
continuous hydraulics hose fixed by clamps on the risers progressively with the descent as well as the two electric
umbilical electric.
"Hot Line" is a line of 1" which is used mainly at the time of the descent of the BOP to provide the power during the
connection of the "Risers", as a backup line and to charge the accumulators. It can be also used to reanimate PODs if
for an unspecified reason they had lost the hydraulic power or had emptied their accumulator of 10 or 20l allowing the
activation of "Riser Stingers Extend Energize" and of "Solenoid Supply". It could also but to a lesser extent to make it
possible to provide the power to the POD if one of the valves of the "Conduit line module" had suddenly refused to
work. However, considering its diameter it would not allow the control of the BOP with the adequate flows.
Before the use of the power on the BOP the lines must be purged (Flushing) in order to eliminate all the dirt which
could be there. There is a special function used for that. In this case, one let pass a certain volume corresponding to
that of the conduits until the seabed plus a margin. Either one asks the ROV to show us the fluid who leaves the
conduits with his colour camera during the purging. One stops when the colour becomes again that of the fluid of
origin (blue for water mixed with Erifon which is the additive generally used).
− Hydraulic Functions of the BOP:
The hydraulic functions of the BOP are activated via 75 solenoid valves controlled by the two electronics of the same
SEM. Each solenoid has two coils and each one of them makes it possible to activate the function even if the other is
not activated. Each coil is fed by one of electronic A & B of a SEM. In this case, the loss of one of electronics does
not influence the operation of the system. There is only loss of redundancy and degraded safety operation. The
electric problems are reported on the error displays of the panels. The hydraulic problems are visible only because the
function is not carried out. In this case one must observe the flow in the conduit supply. In practice, only the functions
of power having a strong flow that makes it possible to detect if a function were carried out.
There are two types of commands coming from surface: Commands common to the both PODs and those specific to a
POD. The specific commands are those of the CVM (Conduit Valve Module) and those of the regulators. They
command only one solenoid valve at a same time on one of the SEM what represents two coils each one activated by
one of electronic A & B on the same POD. The common functions activate two solenoids valves at the same time, one
on each POD whose two coils are fed by each one of electronic A & B.
At the hydraulic level, for the common functions to the both PODs and thus activated by each one of them, the
hydraulic functions are activated by means of a "Shuttle valve" and each side of it is fed by a solenoid of each POD. In
this case, if a POD is lost, the other always allows activation but only if it is hydraulically powered. The same if one
lose one of electronics in a SEM but in this case, the redundancy is ensured by one of the remaining coil.
On the BOP two types of functions coexist. Those activated by electronic A & B of one of the SEM and the others
activated by both SEMs. On the panels, these functions are easily locatable by the colour of marking on the panels.
When the colours are Blue or Yellow, it is about function specific to one of the PODs and thus activated by one
solenoid only. The white colour indicates functions activated by two solenoids and a "Shuttle valve".
We must also remember that the two PODs are not hydraulically powered at the same time and the hydraulic
redundancy implies a manual operation to take place
4.4 Acoustic system.
On the BOP, there is an independent system making it possible to command functions of the "Stack" by acoustic orders
coming from surface. The system described is that of Sonardyne used on boats PAN and PAF. The principal function of
acoustics is to be able to close the well of drilling with "Shear rams" and to disconnect the LMRP even if in addition a
certain number of other functions can be ordered individually. It will be used only in the last resort or if all the other
methods will have failed. The events will guide the method to be used.
It is the case when one loses the hydraulic and electric power on the BOP. This type of event can arrive only at the time of
the loss of Risers at the time of an uncontrolled catastrophic drift of the drill ship. That requires however that the two
systems are in the acoustic range and that the sound can be propagated there correctly. It can not be the case if water is
saturated with gas or if the ship is directed in a bad direction.
The acoustic system is completely independent as it has its own power supply and its own hydraulic resources.
The whole of the system which is entirely located on the "Stack" includes a hydraulic block, the HVP (Hydraulic Valve
Package), a set of accumulators, the acoustic SEM and of two DART assembled on arms with an automatic deployment
system. The HVP contains the valves of hydraulics but also the solenoids ordered by the acoustic SEM. It is fed by
accumulators specific to acoustics. The DART are the transducers connected to the SEM and which makes it possible to
communicate with surface. The SEM which is autonomous thanks to its Lithium battery contains all the electronics of
command.
4.5 ROV commands.
The BOP is equipped with a certain number of plugs and hydraulic valves especially adapted to be able to be handled by a
ROV (Remote Operated Vehicle). It is about a subsea vehicle generally connected to surface and ordered remotely. The
valves or plugs of the BOP are assembled on panels of the LMRP and on the "Stack". They make it possible to activate
functions or to provide hydraulic fluid to the BOP. For the functions, the ROV uses its manipulator arm to make turn the
valves or draw on slings which actuate valves. One must also provide him handles so that it can be maintained there in
position whatever is the current. For the supply of fluid, the ROV is equipped with a pump which makes it possible to
provide the pressure. The fluid is located in a tank containing the hydraulic fluid.
This system is used only as a last resort and when the subsea conditions allow it (buoyancy, visibility). It can be used after
an acoustic disconnection took place. In this case, the LMRP went up on surface but one wants to recover the "Stack"
which does not have any more hydraulic power to function. In this situation, it is at least necessary to open the "Well head
connector" to disconnect it from the wellhead. One can also close the well using the "Middle pipe rams" or the "Shear
rams".
Other systems.
Certain equipment has a system named "Dead man". This system is used mainly on the units anchored like the semi
submersibles. This system which is independent of the normal control circuit starts a sequence of functions of the BOP
when it meets a certain number of conditions. The objective of the sequence is mainly to make safe the well by closing the
"Shear rams" and while preparing with the manual disconnection. That wants to say to put "Stack Stingers" in "Retract"
and "Energize" and by making an "Unlatch" of the connectors "Kill & Choke line". The disconnection of the BOP itself
will have to be carried out by the users but the well is protected in the event of significant drift of the platform.
The sequence of "Dead man" is started by the following conditions:
− Loss of pressure in the hydraulic lines (pressure in the hydrostatic line = pressure).
− Loss of the electric output.
− Loss of communication with surface.
− "Dead man" Armed.
These conditions it should be said rather dramatic generally imply that the risers are already cut. That wants to say that we
do not have any more a means to control of the BOP from surface. When we spoke about manual operation of
disconnection, that is already an exceptional operations which will be made when one can return on the site and control
the well again. One will need to reconnect risers to the BOP and to actuate it with the ROV.
Note: The system must be deactivated when BOP is on the surface to avoid inopportune releases because the pressures can
be equal under certain conditions. It can be the case when the BOP arrives on the surface or during maintenance
operations.
There are also systems equivalent to those of the ROV but ordered using the pressure provided by drill strings connectedon a cone present on the LMRP. The selected functions are activated via two rods which activate only the desired function.
The functions available are not numerous and we have in particular the "Riser primary connector" & "Riser connector secondary". In this system, one starts by descending a drill string equipped with equipment called DART which makes it
possible to fix the drill string on the cone. Once fixed, one descends two rods the one after the others inside the drill string
Each one will make it possible to make pass the hydraulic fluid and sealing off connections. When the commands are
activated, one pulls on the drill string until making break the pins retaining the cone (Shear Pins). When the cones are
taken down, one place the ship in the axis of the BOP and one can pull it towards surface using the straps connected to the
cones. This system was installed on some boats at the origin of the projects then were removed thereafter mainly because
of the obstruction of the straps.
To check the principle exactly.
4.7 Emergency systems.
On the dynamic positioning units, there are two principal systems of emergency disconnection of the BOP: The electric
disconnection and the acoustic disconnection.
On the anchored units, there is not in general emergency disconnection. On the other hand there is a system named "Deadman"making it possible to secure the well when there is not any more means of control of the BOP by the equipment of surface.
In the continuation of the text, we will see in details the various denominations used in these tables.
Electric disconnection:
The electric emergency disconnection is generally named EDS (Emergency Disconnect Sequence). It is used only when the
conditions it not possible to disconnect manually under good conditions. It implies that we can communicate with the subsea
electronics and that the electric power is present but also that we have the hydraulic power. The duration of the sequence
should not exceed 45s to disconnect the LMRP as specified in the API16D.
The emergency acoustic disconnection is generally named EADS (Emergency Acoustic Disconnect Sequence). This sequence
of disconnection is used only when the manual disconnection or the electric sequence (EDS) is not possible. That wants to
generally say that one lost either the communication with the subsea equipment, or the hydraulic or electric power. It requires
having a good acoustic communication with the system of disconnection at the bottom. The duration of the sequence to
disconnect the LMRP should not exceed 45s as specified in the API16D
Séquence du "Deadman":
The "Deadman" is in general used only on the anchored units. This sequence makes it possible to put the well in safety by
closing the "Shear rams" and by retracting the "Stingers" to prepare with the disconnection. Each SEM is equipped with
batteries and independent cards that will carry out the sequence when a certain number of conditions are filled. The hydraulic
power is supplied by a set of accumulators dedicated to this function. The batteries are replaced each year or when the
maximum number of activations is reached.
Panels DCP (Driller's Control Panel) and TCP (Toolpusher Control Panel) make it possible to control the functions of the
BOP and the "Diverter" from the surface. The DCP which can function in explosive atmosphere (Zone 1, gas type IIA,
class de temperature T3) is located in a EEx cabinet of the "Driller's Master Cabine" at the drill floor. The TCP that is not
classified is located in the office of the "Toolpusher" of the rig.
The two panels are equipped with buttons for activating the functions, luminous indicators giving a state and displays of
alarms or analogical measurements. The unit is ordered by means of programmable automats of manuacturer PEP
(Kontron) and is programmed using the Isagraf compatible IEC1131-3 software development tool. The languages used
are either an advanced language of Pascal type, or of logical Grafset or blocks diagrams according to the facilities offered
by each one. In certain systems the automats are doubled to ensure a redundancy of the system. In this case, one of the
automats is in standby mode and becomes active only when it loses the signal "Watchdog" of presence from the active
automat.
The functions of the BOP can be divided into four families:
− The functions of the "Conduit Valve Module".
− Functions of the LMRP.
− Functions of the "Stack".
− Special functions related to safety, i.e. the acoustic system or the "Deadman" following the units.
One can also separate the buttons in two categories: The functions which are activated by only one POD and thus by only
one solenoid from those which are activated on the two PODs at the same time by one solenoid in each. The first areidentified by a background of the color of the POD concerned Blue or Yellow. They are mainly the functions of the
"Conduit Valve Module". The second are identified by a White color. They are mainly the functions of the "Stack". The
orders of the regulators are specific to a POD. That wants to say that the pressure of piloting is not sent on the other PODwhen the instructions are changed.
Like recommanded in the API16D, the functions identified by a Red background are those presenting a risk and to use with many precautions. They are in general protected by a cap which should be raised to be able to activate them. What does not state that one can do what one wants with the others functions. The functions concerned are: The "Riser connector" which disconnects the LMRP from the "Stack". The "Shear rams" which cuts the drill strings which are in the well, "Well Head connector" which disconnects the BOP from the wellhead. At this list, it is necessary to add the
particular functions which are the EDS and the EADS which launch a sequence of disconnection of the BOP. The first one
(EDS) is electric starting from the panels and passes by means of the automats to the BOP. The other is acoustic (EADS)independent of the automats but whose button of release is on the same panel. There can be other systems depending ofthe configuration of the BOP.
Some buttons have a color Red or Green. The buttons of green color indicate the state in which the BOP must be when it is in a configuration of normal drilling. This configuration is called "Drilling mode". One should not confuse this colorwith the state of the function. One could have a function with a button Close in Green and another with the same button in
Red although there is a certain coherence between similar functions. For example "Inner Bleed Valve Open" is red and"Upper pipe rams Open" is green. They actuate different types of functions.
The Vent state which is Orange indicates that the function is desactivated electrically and that the solenoid will open thehydraulic cicruit to the sea. According to the type of valve ordered by the solenoid, it can remain in place or turn over to its position of origin when it has a return spring. The other colors indicate that the function is not related to a configuration
The functions can also be classified depending on the states of the component of the system which they relate to or whatthey carry out. There are functions with two or three states and others with no state and which launch a sequence of orders.
There can be a certain confusion between the physical state and the state of the panel if one does not know the components ordered by the functions. This is why a little hydraulic technology will be approached during this document. One can
quote some typical functions:
− The function "Shear rams" has three buttons on the panels: Open, Vent and Close. The Open button is Green becauseit is the normal position in drilling. The Open one also corresponds to a pressure in the Open cavity of "Shear rams".The Close button is Red because it is not the normal position in drilling. When Open is fed, Close is not andreciprocally. When the Vent button is activated, the distributor of the function remains in position of the last functioncarried out. In this case the lamps "Closed & Vent" or "Open & Vent" are light at the same time. That announcessimply that piloting was cut but that the activated function is that which is lit. Depending of the kind of rams ("STLock"
or "Ram Lock") used on the BOP, the software is treating more states than described above.
− The function "Lower Inner Kill" has two states: Open and Close. The Close button is Green because it is the normalposition in drilling. The Open button is Red because it is not the normal position during drilling. When the Open isactivated, the pressure of piloting is sent to the corresponding pilot valve. When the Closed is activated, the functionpurges the pilot pressure. This is the particular case of functions known as "Fail Safe" which closes the valve whenone release the pressure. Some "Fail safe" functions have also a Close and they do not rely only on the spring. It isoften called "Close assist" but the valve will close anyway if the pressure is released on the Open because of the
spring.
− The function "Conduit Isolation Valve" has two states - Open and Close - but each one of them corresponds to a
pressure of piloting in a different valve. The states Open and Close cannot however be activated at the same time.
There is not position Vent where the pilot circuit is purged except on one state at a time.
− The function EDS (Emergency Disconnect Sequence) does not launch a single function but a sequence of functionsaccording to a sequence programmed in the PLC. It is the case also in another field for the functions of the "Diverter"which configure several valves at the same time (F.ex: "Trip-In mode").
− The function "Deenergize Stinger Seals" purges a certain number of functions before being carried out in order not todamage the stinger seals. The backuground color of the buttons is of the color of the POD concerned.
It is necessary to keep in mind that the state of the lamps and the displays of the panels do not represent the state in whichone wanted putting it while pressing on the button but the real state in which the function in the part concerned is (POD ofthe BOP or Diverter in the HPU). When one presses on a button of a function of the BOP, the order crosses the networkuntil the " Distribution Units", passes by the umbilical until the POD. The command is interpreted in SEM(s) and thestatute is returned towards the panels. It is at this time only that the indicator of the panel indicates the state of thefunction. This process makes it possible to have an exact idea of what occurs in the equipment of destination and not whatone wanted to do. Any detectable error by the system went up to the panel and is displayed. The errors which can bedetected by the SEM are: The short circuit, the open circuit, the overload, overheating and bad insulation or leaks. On thepanels they are indicated either in the alarms display or by a flickering of the function concerned. The "Event Logger" is the tool which allows complete diagnostic in the event of problem. Operational procedures include a daily visit in order to check the errors gone up by the system.
It is necessary to keep in mind that the statute is only electric and does not allow to know if the hydraulic function passed
well. The only way to know if a hydraulic function passed well is to check the volume consumed using the flowmeters as
well as time that that took. This is why, during the surface tests one records volumes and times for all the functions if they are measurable.
Some functions can also be done only under certain conditions of state of other functions. This type of blocking is named
"Interlock". It is the case of the functions:
− The "Riser" and "Stack Stingers" which can be retracted (Retract) or be extended (Extend) only if the "Stinger seals"
are "Deenergized". That avoids the destruction of the seals joints in the contrary case.
Others can also be related to a temporization of the software to make it possible a mechanical function to be carried out. It
is the case of the function:
− The "Lock" of the "Rams": The "Open one" of the "Rams" can be made only after one "Unlock" followed by a certain time (for the Ram Lock).
The functions of the regulators are also specific. The push of the button "Increase" or "Decrease" positions a set point
which will be sent towards the selected POD (in fact both electronics A & B of the same POD) by means of specific
commands. The POD will be then given the responsability to set the regulators independently of the automats of surface
by means of the "Pilot" pressure". The buttons thus do not actuate any solenoid valve directly when they are activated by the intermediary of the panels.
On the DCP and TCP there is a display for the alarms detected by the system. These alarms include the statut of thenetwork, of the power supply, certain analogical values, the redundancy, and the state of the solenoids (short-circuit or open circuit). Buttons "Up" and "Down" make it possible to make browse active alarms that are still not validated and a button "Quit" makes it possible to validate them when they are inactive. These alarms are more detailed in the Event
Logger which must be used in complement for the diagnostic with the possible indications associated with each peripheral.
5.2 DU (Distribution Units).
The DU are two and are named A & B. One of them deals with part A of the system i.e.:
− Part A of the Profibus network and equipment of surface in each panel TCP, DCP, HPU and Event Logger.
− Distribution of the power coming from UPS A.
− Communication with electronics A of the SEM Blue and Yellow.
The other DU provides the same functions but for the part B of the network and the power.
Each DU provides several functions:
− Distribution of all the messages circulating on Profibus towards or from the equipment of surface TCP, DCP, HPU
and "Event Logger".
− Transmission of the messages bound for electronic of SEMs on the lines of data of umbilical via modems. The signal
is in the format "Half Duplex FSK" (20480-24576Hz) and its speed is of 9600bds. The validity of the messages is
controlled by a CRC of 16bits and the checking of the contents of the data.
− Distribution of the electric power to the various panels of surface and equipment of protector by fuses or circuit breakers.
Internal Profibus of the cabinet functions is in RS485 cooper cabling (purple cables) on the other hand the link to the
external cabinet functions on optical fibre by means of the OLM. The RS485 is terminated at each end of the segments
using the switches being on the DB9. Physically, it is about a cabinet with an indicator of power supply for each of
electronic of PODs Blue or Yellow. Some power supplies are protected by circuit breakers and some by fuses to avoid the
propagation of a fault to the other parts of the system. The ratio of transformation of the transformer feeding the SEM via
the umbilical can be selected by choosing a different output. One will be able to adjust the voltage according to the length
of cable. The selection of origin is 230V for 3000m of umbilical.
The power circuits of umbilical are protected by insulation testers (Isometer). When a fault is detected, the circuit is cut
until the reset of the operator and the disappearance of the problem. There is no automatic reset in order to avoid the
inopportune restarting in the event of intermittent breakdown.
Figure 24 DU network
and power circuits.
There are two connectors under the cabinet – one for each POD -
making it possible to connect the testing equipment PETU (Portable Electronic
Test Links). When the PETU is connected to this place, one can control one of
electronic of a SEM by using the software "WinTSIM". It should be
noted that the connection of the PETU implies to shut down electronics
concerned completely in order to avoid the inductive effects generated by the
coil formed by the spool of umbilical when the connectors are removed.
Note: One never disconnects umbilical under tension without
taking the risk to destroy the modems.
These connectors are also used to isolate electronics from the DU
during the tests of insulation of the umbilical.
HPU (Hydraulic Power Unit).
The HPU consists of four
distinct systems in conformity with the recommendations from the API16D:
-
The main hydraulic
power unit HPP (Hydraulic Power Package) with its control
panel and its backup system.
-
The Mixing Unit.
-
The "Diverter"
and its control panel.
-
The accumulators.
The whole of this unit is ordered by one or two redundant depending
of the installations. The HPU is autonomous compared to the other systems. No
order can be carried out rather than from the local control panel. The whole of
the equipment of the HPU are explosion proof (EEx) and must be able to work in
the presence of gas.
-
The hydraulic power unit (pumps):
It has four main electric motors activating the pumps and making it
possible to charge the benches of accumulators of surface. These pumps make it
possible to fill the surface accumulators in 15min to the working pressure
starting from the preload pressure and when all pumps are functioning at the
same time. The starting values of each pump is different so that they operation
not all at the same time except significant need for power. When the swapping
of the pumps is not done by the software, it must be done manually by changing
the start point of each pump. The fluid is never directly sent towards the BOP
but it is used to fill of the accumulators being on the surface. Dump valves
make
it possible to prevent the fluid from exceeding the operating
pressure. Depending of the systems, the pumps are started either by an automat by using the
information of pressure, or directly by means of a pressure transmitter with
minimums and maximum.
The pumps can be deactivated, work manually or automatically by using pressure measurements. On some systems, the starting values of the pumps are automatically permuted by the program in order to prevent that it is always the same one which turns. When it is not the program which manages starting, the pumps must be permuted manually. There are independent limiting device of pressure which allow bypassing any defect of the automat
-
Emergency
pneumatic pumps:
They provide the same function that the electric pumps but function
starting from the reserves of 5bar rigs air. They are useful only in emergency
when the electric power is cut. One can cut the electric output when there are
risks of explosion or lose the power at the time of a general blackout of the
rig. Their capacity must be the same one as that of the electric pumps.
-
The unit of mixture (Mixing links):
This unit includes four tanks of which one of great capacity
containing the mixed fluid. This tank must at least be able to contain twice
the capacity of the accumulators at
surface pressure rating (350bar) plus the volume of the largest of the benches
of accumulators (see API).
Pneumatic pumps.
The four fluids used are as follows:
-
Water: This water comes from the supply of the rig.
It must be de-chlorinated as much as possible in order to limit the chemical
reactions in the hydraulic elements (joined or metal). In the contrary case one
notes corrosions at various levels of the valves, which accelerates ageing and
implies higher frequencies of maintenance. The seals are also damaged by the
chlorine.
-
Glycol: This liquid makes it
possible to avoid the freezing of the hydraulic fluid in the great depths of
water where the temperature can be close to 0°C. The concentration is
regulated according to the seabed
temperature. Even in the
tropical
countries, the seabed temperature can reach only a few degrees in deep water (2° at 1500m in Angola).
Figure 27 Mixing
unit.
-
Lubricant: This liquid makes it
possible to lubricate the hydraulic functions. It is biodegradable because some
BOP still rejects the fluid of return of the hydraulic functions to the sea.
The concentration is regulated according to the recommendations of the manufacturer.
It is preferable not to have a too high chlorine level in order to limit the
chemical reactions on metals. "Seals
Plates" of the valves are particularly sensitive. The more common
lubricant used is Erifon HD856 in a ratio of 100/1. It has properties
anti-wear, anti-corrosion and is not attacked by the bacteria because it
contains anti-bacterial agents with broad spectrum. Moreover, it can be
rejected into water without problem because it is biodegradable.
-
Bactericide: This liquid makes it
possible to avoid the bacterial invasion within the hydraulic piping. If the
lubricant contains some, it is not necessary to put some. They should not be
chlorinated products because they attack the seals and the metallic parts.
The mixture of these liquids is determined by rotary switches being
on the control panel. Each pump is equipped either with a flow meter or with a
temporization making it possible to ensure the mixture knowing the flow of the
pump function of the time. One proceeds initially by the filling of the tank
containing the mixture by a defined quantity of water and then by the
contribution of the various components of the mixture. The homogeneity of the
mixture is ensured by agitators in the main tank. The unit is managed by a programmable
automat which activates the various pumps of the system according either to
temporization or of measurements of flow. It controls also the levels of the
tanks in order to avoid the overflows.
The National
Aerospace Standard (NAS) 1638 defines a standard describing the
level of contamination of a fluid with a factor from 00 for the highest
contamination and 12 for the lowest. The BOP requires values between NAS08 and
NAS10.
-
The ordering of the Diverter:
The "Diverter"
can be ordered from the panels TCP & DCP but also hydraulically starting
from the HPU or on a backup panel. Orders of the "Diverter" are sent to the automat of the HPU and the panels by
means of the Profibus. It is in the
automat that they are carried out. The information displayed on the panels
corresponds to the return of pressure of the activated lines and not to the
electric function. That makes it possible to make sure that the function is
well carried out on the hydraulics side.
At the time of a breakdown of one of the pressure transducer, the
result of the activation of the function is not visible. That can prevent other
commands from being carried out because there are inters blockings between
certain functions. In this case, check the pressure transducer and replace it
if needed. There are often manifolds making it possible to isolate the circuit
and change these pressure transducers with the pressure.
On certain systems, the pressure of closing of the "Packer" as well as the high and low
joint of the "Telescopic Joint"
is adjustable. We can also have a system to pass from one "Packer" to the other when one of
them fails.
The manual orders being on the "Diverter panel" of the HPU directly actuate the
Figure 28 Diverter
panel.
corresponding valves without the use of the automat. The display of
the states on the panels corresponds to information of pressure as it is the
case for the electric functions passing by the automats of the panels. That
allows a safety in the event of loss of communication or power supply fault.
The orders of the "Diverter"
are described below.
-
Accumulators:
They are manufactured in
conformity with the standard BS7201, BS5042 part 1 or ASME section 8.
There is however several standards of available volume in this
domain but the companies can also impose their own constraints. One will take
most constraining to make calculations. They are in all cases organized so that
the lost of one bank will not reduce the total capacity of more than 25%.
API RP 16CE.3.4.1:
Require enough volume to open and close completely all the "Rams" and annular with pressure 0
and to have 50% of volume in reserve to the pressure of 350bar (5000psi). The
remaining pressure after the opening and closing of all the "Rams" and annular must be larger
than what follows:
The theoretical pressure minimum of closing of one of the "Rams" or to be able to open and
maintain open one of the valves "Kill"
or "Choke", both with the
maximum pressure of work of the BOP.
API RP 53 13.3.2:
Require enough volume to close and open all the "Rams" and annular starting from
the position open
until total closing
to basic pressure
0. There must
remain a
Surface
accumulators.
minimum accumulator pressure equal to the preload
initial + 200 psi. All this will be done with the stopped pumps.
The USA MMS
(The Minerals Management Service) CFR 30, section 250.406.D.1:
Require 1.5
times volume required to close and maintain closed all the equipment of the BOP
to the basic pressure. There must remain a pressure of minimum accumulator
equal to the preload initial + 200 psi.
NPD (The
Norwegian Petroleum Directorate, 1998) Ya-001a; 1998, Section 41. The Control
Section for the "Blowout Preventers",
This is the most constraining. Require to be able to close, open and
close all the "Rams" plus
25% of the volume of closing of one of the functions. The arrangement of "Rams" consists of annular, a "Shear rams" and two "Rams" which can be closed on the drill strings.
The Diverter.
To check with the drillers, API
RP64 and West reports/ratios.
The principal function of the "Diverter" at the time of an eruption with low pressure is to
redirect the fluids controlled or not controlled coming from the well towards
distant parts from the people or equipment which ensures drilling in order to
ensure the safety of it. This device is neither made for the high pressures (in
general, 300bar or 2000 psi) nor to completely stop the flow of the fluid
coming from the bottom. In normal operation, when there is no gas, it redirects
the drilling fluids towards the mud circuits. Each rig has a different circuit
and what follows tries to give a general overview. The fixed part of the "Diverter" is located on the surface
under the drill floor from where one can extract his removable part at the time
of the operations requiring a more significant passage.
The Diverter is used on the floating rigs in the
following cases:
-
For the control of the increase of fluid at the time
of gas arrival coming from the formation.
-
To reabsorb gas
that can be trapped between the BOP and surface.
-
Like additional safety equipment in the event of
uncontrolled eruption and
-
When the pressure of fracturing is low and that one
cannot make circulate heavy mud to kill the well. In this case, control with
the BOP alone can be a problem.
The three principal modes of use are as follows:
-
Drilling: It is the mode used during
drilling. The annular is opened; the flushing fluid circulates normally in the
mud circuit while passing through the degasser.
-
Diverting: It is used when one wants to
control the well. For example at the time of an arrival of gas. In this case,
the annular is closed and the flushing fluid is redirected towards one of the
lines of discharge "Port Overboard"
and "Starboard overboard".
-
Tripping: This mode makes it possible
to descend or pull the drill string and keep the circuit sealed. That makes it
possible to control volumes which enter and leave the well following the
operations. When the drill stings are gone up, one fills the well by means of
the "Fill-in valve". The
surplus fluid is recovered when they are going
down.
Each mode is directly activated by adapted buttons being on the DCP
or TCP and which actuates the corresponding
valves. There is also a manual mode making it possible to open the
valves independently. However, only the panels are controlled by inters
blockings between functions (Interlocks)
which prevent from making errors of configuration. This is the case for
example, when we try to open a discharge valve in drilling mode. There are also
temporizations which prevents annular from being closed as long as one of the
dump valves is not open.
Different parts of
the "Diverter":
-
The "Annular":
-
The dogs (also "Lockdown dogs" or simply "Dogs"): They are pistons that make it possible to maintain
the Diverter in place in the body. They must be energized during normal
operation and deenergized when one want to remove the "Diverter" (Seals deenergized and pistons retracted). The
"Diverter" must be removed
completely at the time of certain operations as the installation of tubings,
the descent of the risers or other special operations.
-
Pistons (also "Piston stabs" or "Stabs"):
They are kinds of hollow fingers which one can extend or retract to
connect oneself between the fixed body of the Diverter and its removable part.
Only the
seals ensure the sealing.
-
Joints (or "Seals"):
Figure 31 Diverter mud circuit.
They are retractable seals that make it possible to ensure the
sealing between the body of the "Diverter"
and the moving part of the pistons. They must be energized before the fluid
does not pass and after the pistons are wide.
-
The valves:
The valves must be able to open when they are subjected to the maximum
operating pressure. The diameter of opening must be that of the lines on which
they are connected. They are activated remotely by panels TCP, DCP or on the
Diverter part of the HPU panel.. The "Diverter"
part of the HPU and in the "Moon
pool" are purely hydraulic and do not use an automat to be able to be actuated.
-
Conduits:
The conduits of discharge must be large diameter and with as less
elbows as
Figure 32 Diverter
cut.
possible to be able to support volumes of significant flows. They
must also resist abrasion because the gases generally contain all kinds of
materials coming from the bottom. The others conduits will be simply adapted to
flow necessary.
-
The electric control parts:
All the commands of the "Diverter"
can be activated from TCP or DCP panels. In this case, information are transmitted from panels by the
intermediary of the Profibus network
towards the automat of the HPU. Information of status is then turned over to
the panels by the same way for their display. Displays correspond to the
pressures in the various lines and not to the electric status of the function.
One is sure that the function was well carried out when an indicator is lit.
Only the state of the indicators is taken into account in the program of the
automat. It should however be made sure that the pressure pick-ups are quite
functional. In the contrary case, one could be blocked because certain functions have inters blockings and
require to have other functions in a particular state before being carried out.
The "Diverter" part of HPU
automat does nothing but transmit the orders to the functions and return the
values of pressure in the various lines to the panels. The logic of the "Diverter" (temporizations, inter
blockings) is carried out in the panels only.
There are also functions of adjustment of the regulators. One can
quote for example that of the "Packer".
The principle is the same one.
-
The hydraulic control part:
They are manual valves and for adjustments of regulators which are
on a separate part of panel HPU and in the
"Moon pool". The information of feedback of the state of the
various functions and the regulators is made by the intermediary of the returns
of pressure.
Treatment of an
eruption by the "Diverter" is described in API RP 64 and 59. We will
make a description later in the text.
Equipments of test.
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The "BOP test
box":
The "BOP test box" is a unit including
only five buttons and a display. It is connected on a plug being near to the
"Moon pool" towards the
place where are made the tests of the BOP. This plug is connected directly on a
serial link of the automat TCP panel. Inside of the panel
of the TCP a key is making it possible to
give control to the "BOP test box"
instead of the TCP panel. In this case, the TCP is completely deactivated. This
unit has almost
the same functionalities as the TCP with all controls but can be
used in the "Moon pool" by
the hydraulic technicians to control the BOP.
The box is equipped with several buttons: A button "Up" and "Down" allowing selecting
the function
which is displayed, three control buttons whose function is displayed on the
lower part of the
BOP
test box.
display and a key "Enable"
which makes it possible to activate the selected function when it is pressed at
the same time as the button of the function. The functions being able to be
assigned with the three keys are for example: Close/Vent/Open for the rams,
Latch/Vent/Unlatch for the annular ones, Inc/None/Dec for the regulators. But
we can also activate the function with two buttons.
The PETU (Portable Electronic Test Unit) is a unit making it
possible to communicate to a SEM with a PC equipped with driving software
called TSIM (DOS version) or WINTSIM (Windows version) according to the
versions. This software contrary to that of panels TCP or DCP does not contain
any limit of operation and thus do not have any inter blocking of functions.
Moreover, it does not use the same chart as the panels. That wants to say that
all the operations are possible and that it must be used by a skilled user.
It is made of a power supply for the two electronics of the SEM and
of a modem making the interface between the RS232 of the PC and the signals
coming from the SEM container. This unit is mainly used for diagnostic in order
to be able to test individually the
functions without passing by panels (DCP or TCP). Electronics A or B with which
one communicates is selected by a switch. On the other hand the two electronic
are powered at the same time. That wants to say that if one passes from one
electronic to the other, the function remains activated on the preceding one.
That can cause confusion and it is necessary to be very attentive with this problem
during the tests.
The PETU can be connected directly on a SEM or on one of the plugs
below the DU. When one passes by the DU,
one communicates with the SEM via one of umbilical but only one of
electronic is available at the same time because the plugs are concerning only one electronic of the SEM at a time.
To test other electronics, it is necessary to move on the other DU. When one
communicates directly with the SEM, the two electronic can be selected by the
selector being on the front face of the
PETU. In all the cases, no connection must be done under tension. Direct
connection on DU is used when one wants to order a POD which is assembled on
the LMRP in operational situation. Direct connection on the SEM is used rather
when one wants to make functional tests on a POD on the test bench. The PETU is also equipped with detector of
problems of insulation. That makes it possible to test the quality of the
insulation of umbilical when it is connected on one of the "Distribution Units". In this case,
one passes by the umbilical to communicate with the SEM.
The UPS (Uninterruptible Power Supply) is
equipment which allows remedy to main power supply failure on the electric
equipment. The system "Mux"
is equipped with two inverters feeding each one a different DU. Each of them is
fed by a different circuit coming from the generators of the rig. One arranges
wiring to connect them on different distribution systems so that the two
circuits cannot be cut at the same time. In the same way, the site of each UPS
is selected so that the loss of one of them cannot affect the other. The API
16D specifies that the minimum autonomy of the inverter must be of 2h in normal
operation.
In the general case, the inverter "One line" contains: Two converters - an AC/DC (alternate to
direct current) and a DC/AC (direct current to alternate) -, a circuit of
"Bypass" and batteries. It
contains also other elements not represented like filters, of the para
surtensors and others which make it possible to protect the equipment that it
feeds.
Note: An inverter "One
line" provides the power after rectification. An inverter "Off line" contains a switch between
the "Bypass" and the exit
of converter DC/AC. Under normal operation, converter AC/DC of input charges
the batteries and the converter DC/AC of output provides the power to the
consumers starting from the direct current of the batteries. The "Bypass" is open. The batteries are
said in "Floating" mode
because charges and discharge are simultaneous.
When the input power is lost, converter AC/DC is not supplied any
more and converter DC/AC takes over and provides an alternating voltage by
getting the power from the batteries. The "Bypass" is always open. The lifetime of the batteries depends
on the load but also on their capacity expressed in Ah.
Example: If one has batteries of 18Ah and that the load consumes 6A,
the batteries will hold 3h to the maximum. This duration is reduced in function
of several parameters whose principal ones are: the age of the batteries, the
number of discharges carried out, environmental conditions, the temperature and
the level of load at the time of the cut.
The "Bypass" can
be activated either manually for example to make a maintenance inside the UPS.
In this case there are circuit breakers making it possible to isolate the
circuits. The "Bypass" can
also be activated if one of the components of the UPS is defective: Batteries
at fault, converter at fault, overload, overheating.
The maintenance of the UPS on the BOP can be done only when this one
is on the surface. It consists mainly of a visual inspection, the test of
alarms but, also in a test of discharge of the batteries. This one can be still
carried out either on the normal load or by supplying power resistors. There
are also systems making it possible to test the internal resistance of the
batteries using high frequencies without disconnecting the batteries. These
tests are to be preferred to the discharges of the batteries because that
decreases their lifetime. The replacement of a defective UPS requires at one
time or another to cut the power unless
having a system of external "Bypass"
with the UPS. In this case, one loses the redundancy on the circuits of the
panels and on the SEM. This operation can be done only in particular phases of
the operations and with the agreement of the customer. An analysis of the risks
must be made as a preliminary.
Reels and umbilical.
The reels are equipped with 3100m of umbilical. There are two
umbilical named Blue and Yellow in correspondence with the colours of PODs. The
umbilical is rolled up or unrolled using a pneumatic motor ordered using levers
being either on the support of the reel or on a remote control panel close to
"Moon Pool" in view of the
cables.
At the interior of the reel, there is a of junction box EEx (Reel
Frame Mounted EEx JB) which establishes the link between the wires of the umbilical and those
coming from DU A & B. This junction box turns with the cable and contains a
simple terminal block but also in certain cases, a converter of optical signals
towards analogical. From this junction box, one passes by a slip joint towards
the junction box being on the support of the reel (EEx JB) bound to the "Distribution Units".
All the junction boxes of the reel can function in explosive
atmosphere (EEx) because they are in a space close to "Moon Pool" which
can contain gases
coming from the
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well. The opening of these junction boxes is requiring to make a work permit and can be done only when the risks of explosion are null. It is by these reels which the signals and the power are sent to the PODs being on the BOP. That is in these reels that pass the umbilical with the two cables of signals and two cables of power coming each one from one different DU with in addition optical fibres not used at the time of the drafting of this document. While leaving the reel, the umbilica
l
pass by
pulleys of returns. They are then attached
at regular intervals
by fasteners (Clamps)
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risers at the time of the descent of the BOP. On the BOP the umbilical is attached by ropes along the flexible of "Choke" and "Kill", one forms then a loop and one connects on the RMJB (or SEJB). The loop makes it possible to prevent pulling directly on the connector if for a reason or another there was a tension on the umbilical. On the surface, the umbilical are connect to a goose neck under the "KT-ring" on fasteners being on the "Outer barrel" of the "Telescopic joint".
on theThe umbilical consists of several external reinforcing jackets, of
an intermediate layer made up of the 8 wires of power of 2,5mm2 and an internal
layer of 4 wires of 1,5mm2 surrounded by a shielding that are used for the
signals. It has also a conductor containing 6 optical fibres not used in our
application. At the origin, the optical fibres could have two uses: Either to
transmit video signals from the bottom, or to make communicate the equipment of
surface with acoustic transponders being at the bottom. This system conceived
by Sonardyne has as a name ROVNAV.
The signals of data are positioned in order to induce as less as
possible coupling between the two signals. The signals for that are cabled in
cross and not face to face.
Note: All the
rigs do not have umbilical with optical fibres. It is the case of the PSP or
PNA.
The Event Logger.
The Event Logger is a simple PC equipped with a Profibus card and making it possible to trace the activities on the
panels, to recover alarms and to visualize analogical values and the state of
the solenoids coming from the subsea equipment or from the HPU. It has also
filters making it possible to make research according to various criteria to
find the dates and hours of the events. It can be used as well as informer to
manage the conflicts of interests in the event of problems or of tool for
diagnosis. It is contractual equipment and which must always be under
operation. The software is presented in the form of four panels containing
different information.
-
"File view":
This panel browses all the events occurring on the network. It makes it possible to quickly visualize the state of the various equipment of surface and subsea (if they are Available or not). It also makes it possible to mark certain lines when a certain text is found and to add comments in the files of recording of the events. It is not the more used
The Event Logger records all the events occurring on the BOP in
textual files at a rate of one per hour. The screen of this panel makes it
possible to visualize these events, to apply filters by keywords or dates and
to mark certain parts of the record containing a certain text. At the contrary
of the precedent, it can in certain cases not be up to date from current
information. This is why there are buttons "Update". This screen is
used the most during corrective maintenances to identify the problems.
The zone "Status Data" of this panel gives the indications
of the state of the solenoids of the SEM selected in the zone "Select
SEM". When "Show activates SEM" is selected, one displays the
state of the SEM indicated in zone "Active SEM". The "Active SEM" is selected on
panels DCP and TCP.
The normal state of the solenoids is either "On" is
"Off". When a solenoid is at fault it is marked "Break". When they are two solenoids
for a function, for example for ("Shear
ram" Open/Close), we have a value in both Solenoid 1 and 2 columns.
When one is On the other is Off in normal conditions. The Vent corresponds to
the state where both solenoids are Off. For the functions with only one
solenoid, only one column is filled and the state is On or Off.
The zone "Analog data" indicates the analogical values read on the SEM selected in the same way that for the state of the solenoids. The column "Log" makes it possible to avoid recording the value associated with the line for example when it fluctuates too much. The values are recorded when the change exceeds a certain percentage of the preceding
value. This value is configurable in the initialization file (.ini)
of the Event Logger. The graph makes it possible to visualize an analogical
value function of the time. When a sensor is at fault and when this defect is
detectable, the Event Logger indicates a "Break". It is the case when
the values are below a certain value (most of the time < 13107).
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"Diagnostic HPU view":
This sight is identical to that of the preceding one.
When there is two PLC in the HPU, zone "HPU displayed" displays that
which is selected and indicates that which is active.
-
The configuration files of
the Event Logger:
The parameters of the Event Logger are situated in a
".INI" file pointed by the file E_Logger.ini. This is in this file that we have the list of the functions of the
BOP and HPU, the analogue values measured and the alarms. The format is a standard formatted text with delimiters of zones between
brackets.
The control power and signals arrive both by the
intermediary of umbilical coming from both "Distribution Units" for electronic A and B. The umbilical
contains 8 power cables (2,5mm2) and 4 data (1,5mm2).
The wires of data are gathered in the central part of the cable and are
surrounded by a shielding. It is fixed along the risers by fasteners which
prevent that the weight of the cable pulls on the higher part.
At the surface level, the power and the signals arrive from the DU,
passes in the slip joint of the reel to join the bottom via the umbilical. At
the bottom the umbilical is terminated by a subsea connector rather complex
that is connected on the top of the RMJB which distributes the power and the
signals to the SEM. The RMJB is only a subsea junction box for the power and
the signals bound for the SEM and of the RCB.
The SEM is the only element to communicate with surface by the
intermediary of the umbilical. It receives measurements of the various sensors
via:
-
The RCB for measurements of flow, inclinations of
the risers, pressures and temperatures "Kill" and "Choke"
and of the sensors of proximity.
-
The STM for the pressures and inclination of the POD.
The communication between RCB and SEM is done via the RMJB or SEJB
when it exists. In the contrary case, the RCB
is connected directly on the SEM. On certain rigs, it exists only one
RCB which communicates in this case with the two SEM at the same time. The
electronics of the SEM is doubled but each SEM is fed only by one umbilical.
That can generates problems of redundancy when the umbilical or its connector
are faulty. All the connectors are of manufacturer Seacon PBOF or ODI for the
connectors allowing a connection under water (known as Wet-Mate, model ODI
Nautilus). It is the case of those of the POD and those with the handle for ROV
to connect to the sensor of Pression/Température being on the "Stack".
General information on the hydraulic systems.
Hydraulics of the BOP arrives from surface by two principal lines
called "Conduit line Blue"
and "Conduit line Yellow"
functioning at a pressure of 340bar (5000psi) and on some rigs by a secondary
line, the "Hot line" at
205bar (3000psi).
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The "Conduit lines" are rigid pipes attached on the "Risers" and connected each other. The "Hot line" is a continuous flexible device of 3000m which is fixed by fasteners located all along the risers at the time of the descent. The pressure on these lines is provided by the HPU. The commands are on the panels and the hydraulic unit. The "Hot line" is ordered separately on another panel.
At the end of both "Conduit
lines" Blue and Yellow, the fluid arrives on the BOP, passes in two
flexible hoses (Coflexip) to the "Conduit Valve Module" which
contains certain numbers of valves allowing to Open or to Close certain feeding
circuits of fluid. The flexible devices make it possible to accept the
movements of the subsea "Flex joint"
when the ship moves on the surface. In the "Conduit Valve Module", the fluid crosses the "Isolation Valve" to be distributed
on the pilot circuit, the power circuit and the accumulators by the
intermediary of the different POCV (Pile Operated Check Valve).
At the exit of the "Isolation
Valve", there is also a "Flush
valve" which makes it possible to clean the conduit lines after their
connection by means of the hydraulic fluid under pressure before opening the
hydraulic systems of command. All the valves of the "Conduit Valve Module" are controlled by the intermediary of
the POD while passing by from the "Stingers".
They are retractable conduits allowing the fluid to pass between the LMRP or
"Stack" and the POD. That
implies that the "Stingers"
are "Extend" and "Energized" to be able to activate
these functions.
The circuit of "Hot line"
which is separate makes it possible to keep the hydraulic power on the BOP even
when the "Conduit lines"
are isolated at the time of the connection of the risers. It can also be useful
in breakdown service when one of the conduit lines leaks or to reanimate a POD
when there is no more hydraulics of piloting to actuate the "Conduit Isolation Valve" but only
if the "Stingers" are in
position "Extend" and
"Energized". This line is
not present on all the installations. In this case, it can be difficult to
revive a POD if it is not on the surface.
The power circuit which is purged at sea when the POD is not
selected goes directly on the regulators then on the valves of power in direction of the hydraulic
functions. There is in general a regulator called "BOP manifold regulator" which controls the functions of power
other than the annular which have their own regulator. This circuit is also
equipped with a flow meter which makes it possible to measure the fluid
consumed by the functions and to check that it were indeed actuated. Without
the flow meter,
we would have only the electric confirmation of the execution.
The pilot circuit passes by a manual regulator to lower the pressure
from 340bar to 205bar. It moves directly towards the solenoid valves which
control the valves of powers or the regulators. Certain solenoids order the
functions directly when volumes are not significant. The pilot circuit is also
equipped with an accumulator which makes it possible to reanimate the POD when it was isolated from the main circuit.
There is a subtlety in this circuit related to the fact that PODs
are removable (or retrievable). PODs are equipped with "Stingers" which is retractable
elements making it possible to leave the POD without having to disconnect the
hydraulic hoses of the unit. The fact that it is removable is useful for
maintenance when one removes PODs from the LMRP but more especially to be able
to give the possibility to the LMRP of disconnecting itself from the "Stack" without tearing off the
hydraulic hoses.
When a POD is started and that it does not contain any pressure, it
is impossible to activate any function. When one is on the surface, one
installs a line directly on the pilot circuit of the POD in order to be able to
put the "Stingers" in "Extend"and "Energized"
and to open the "Solenoid valve
supply". When one is at the sea-bed, one can count only on the
accumulator of pilot circuit to keep enough pressure unless there is a ROV
panel to supply the pressure.
PODs .
The PODs are electro-hydraulic elements containing the electronics
of command of the BOP but also the hydraulic of power and the pilot circuits.
They are positioned on different places of the LMRP called Yellow and Blue.
On the boats, Blue is in general on port side. It is necessary to differentiate
the name of the Blue site or Yellow of the name of the POD which are numbered
from 1 to 3. Two of the PODs are on the BOP and the third is that of
replacement. The numbering of the POD is significant because it conditions all
the preventive maintenance.
The PODs can easily be removed from the LMRP because they are simply
fixed by their own weight (~7T) and two kinds of fingers actuated by pistons,
the "POD lock" which
maintain it in place. The positioning of the POD on the LMRP is facilitated by
studs of centering. On certain BOPs, the POD are recoverable from the seabed by
using a winch in order to carry out a maintenance. They are installed in
supports making a guide called "Funel".
These guides allow their extraction and their reinstallation when one goes down
again after repair. In this case, the hook of lifting of the POD is equipped
with a sling which makes it possible for the ROV to hang it to the hook of the
surface winch.
The POD can be separate physically in two parts:
-
The higher part which contains the container of the
electronic of command - the SEM - and the hydraulic part of piloting. Piloting
includes the solenoid valves, the accumulators of the regulators and pilots and
the manual regulator of the pilot circuit (set at 210bar).
-
The lower part contains "Riser Stinger", "Stack Stringer" and an electric connector being able to be connected and disconnected under water, the "POD locks", the regulators and the distributors for the power circuits.
The lower part contains "Riser Stinger", "Stack Stringer" and an electric connector being able to be connected and disconnected under water, the "POD locks", the regulators and the distributors for the power circuits.
Note: The support part described in the preceding diagram is used
only in surfaces to support the POD during the tests.
Various components of
a POD:
- The SEM:
The electric part of command is contained in a subsea
container called SEM located in the high part of the POD. Each container
contains electronics A and B in connected to both "Distribution Units", respectively "Blue A" and
"Blue B" or "Yellow A" and "Yellow B".
The electric power and the control signals going to the SEM arrive
by umbilical Blue or Yellow on the POD concerned by means of the electric
connector being on the lower part of the POD. This connector can be
disconnected and reconnected under water but not under tension. It is used with
the "Stingers" to make the
POD recoverable. It allows also the disconnection during maintenances when one
removes the POD from the LMRP to put it on an external support.
The SEM is also connected to the STM (Subsea Transducer Module) which provides various measurements of pressure and slope
of the POD.
On the lower part of the SEM the 13 "Pie connectors" making it possible to connect each one 6
solenoids valve. Certain connections are for test and are not used for the
solenoids. The image of right-hand side shows part of the bottom of the SEM
containing these connectors. A solenoid is connected on one of them. Before
being inserted, each connector of solenoid must be coated with a fine layer of
silicon grease in order to ensure the sealing. There are precise procedures to
carry out this operation. When one of these connectors is replaced, one must
check the polarity of the signals of the solenoids. Connectors not used must be
equipped with blind plug in order to protect the connections from sea water.
The SEM contains an internal moisture and pressure sensor which makes it possible to monitor its state. When both the pressure and moisture inside the SEM increase at the same time, one can suspect a leak. These sensors are also useful when one closes again a SEM after maintenance. In this case, the SEM must be purged with nitrogen until moisture lowers until a value lower than 20%. This process can last more than one hour depending of the initial level of moisture and the temperature. At the time of this operation, the pressure in the container should never exceed 1bar. It is preferable to carry out this operation when the temperature inside the container is stabilized. The SEM
Figure 48 SEM.
Figure 49 SEM pies.
contains also a temperature
switch enabling him to start fans in the event of overheating. Overheating can
arrive on the
surface when the temperature is high. After immersion, the
temperature drops rather quickly what can generate condensation if the SEM were
not purged correctly. In this case, one can have false information of moisture.
- The STM:
The STM is a container containing the inclination and pressure
sensors. It is connected directly to the SEM by a subsea cable. The pressure
sensors are those of piloting (Pilot pressure) and the values after regulation
(Readbacks pressure) of the regulators as well as various lines of hydraulic
power. It measures also the hydrostatic pressure which makes it possible to
correct displays of pressure readings on the panels. In the contrary case it
would be necessary to subtract the hydrostatic pressure from the values
displayed according to the depth of water. These sensors are marked
"PTx" in the following
There is also an
internal pressure sensor which makes it possible to detect a water leakage. In
this case, the pressure increases in general rather slowly but regularly. It
can also stop either because the hole was closed or in consequence of
a pressure balancing. In this case, very little imbalance will
involve a repetition of the problem.
The sensors of inclination X & Y give the angles of the POD compared to the horizontal one. Theyare useful in conjunction with the inclinometer being on the top of "Flex Joint" to give the differential angle between the BOP and the risers. The value obtained is transferred to the surface in the consoles of the dynamic positioning of the ship. When the angles exceedsome limit, the consoles set an alarm Yellow orRed. In this case, the drillers must be ready todisconnect the BOP. In practice these angles are used little and one rather uses concentric circles around the position of the well projected on the surface. It should be noted that the POD being installed the ones at the opposite to the other with the same assembly for the STM, one of the POD will give values reversed compared to the other. This problem is corrected by software.
- Hydraulics of piloting:
Hydraulics of
piloting consists of 75 (13*6 possibilities) solenoids valves 1/8" 3/2
ways being on the sides of the high part of the POD. Each solenoid valves is
connected electrically on the pies connectors of the low part of the SEM. The
hydraulic part is screwed on a plate common to a line of solenoids and drilled
of hydraulic conduits for each one of them. The return is common to all the
solenoids of the line what always does not facilitate diagnoses in case of
individual leak. Hydraulics of piloting is fed by the "Solenoid supply" circuit coming
from the LMRP by the intermediary of "Riser
Stinger". Generally there is a filter at the entry of the circuit in
order to eliminate the impurities from the hydraulic fluid. The pressure is
controlled in the POD by a manual regulator set at 210bar (3000psi) starting
from the 345bar (5000psi) coming from surface.
An accumulator of 20litres is installed before the regulator. Its
function is that of buffer but also of reserve of power to launch the POD in
order to recover the power from the outside hydraulic circuit. Indeed when the
POD starts the stringers are in a position unspecified and it would be
hazardous to put the power without to have configured them correctly. The
accumulator makes it possible to put "Riser
Stingers" in the good position i.e. "Extend", "Seals
Energized" then to open "Solenoid
Supply" (it is supposed that the power is provided to the CVM or
Conduit Valve Module). Before moving the "Stingers", one must make sure that "Stinger seal" are de-energized in order not to damage them.
One must also make sure that no pressure exists on the lines. Certain functions
requiring small flows are fed directly not the solenoid valves. It is the case
of the regulators, "POD Lock"
and "Riser Stinger". The
others use distributors controlled directly by the solenoids valves.
As "Upper Annular"
is located on the LMRP, its order is also carried out by the intermediary of
"Riser Stinger" after
having set the regulator being on the POD. This regulator is adjustable from
the TCP or DCP panels.
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Hydraulics of power:
The hydraulic systems of power are fed by the intermediary of the
circuit "POD Supply" after
being regulated by means of regulator "BOP
manifold regulator". This regulator can be controlled from the two
surface panels. Only the annular have their own regulators adjustable from the
panels. According to the required flows, one uses is distributors 1/4",
3/4 ", 1 "or 1"1/2. The power circuits intended for the "Stack" pass by "Stack Stinger". The other circuits
pass by "Riser Stinger".
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The regulators:
The regulators are generally three: One for the "BOP manifold Regulator" and two for
the annular "Upper" and
"Lower". They are
1"1/2 because volumes to be supplied are significant.
The regulators are ordered via two solenoids
valves. The pressure of piloting of the regulation is provided by accumulators
which are loaded at the set point pressure by the intermediary of the solenoids
valves. One of them is used for increase (INC) of the pressure i.e. for the
filling of the accumulators. The other is used for the decrease of the pressure
(DEC), i.e. the emptying of the accumulatorsEach accumulator
is preloadwith a different pressure
in order to be able to cover the range of the pressures. Two pressure sensors
are assigned with each regulator. "Read
Back pressure" is getting the pressure at exit of the regulator and
the "Pilot pressure" gets
it at the level of the accumulators on the line of piloting. The regulation is
carried out directly by the SEM while following the values of the "Pilot pressure". The panels on the
surface do nothing but sending the set point instruction towards the SEM controls thepressure by software
during 3min then lets the regulator
control starting from the pressure of piloting obtained at the end of the
period. If there is a leak in the pilot circuit, the pressure go down
slowly but it
will not go
up by itself
and one will
have tomanually compensate
for it on the panels or to eliminate the leak.
In the contrary
case, the regulated
pressure willprogressively go down
function of the lost of pressure in the piloting circuit. The solenoids valves
of the regulators are the more used of the POD. They must thus be supervised
carefullysurface maintenances.
- The
"Stingers":
The "Stingers"
are two: "Riser Stinger"
and "Stack Singer" (the
largest). Both are used to let the fluid pass between the LMRP and the POD or
the POD towards the "Stack"
while allowing the POD to be removable.
"Riser Stinger"
which is connected in a female receptacle of the LMRP (not represented on the
diagram), receives the fluids coming from the "POD Supply" and "Solenoid
Supply" directly coming from the CVM (Conduit Valve Module). At exit, it let pass the piloting of the
functions specific to the LMRP as well as the orders of the "Upper annular" coming from the POD
after regulation.
The "Stack Stinger"
when it is extended connects in a female receptacle being on the "Stack". It feeds the majority of
the functions of power in 345bar (5000psi) and the others like the annular
or "Riser
Connector" are regulated in the
POD before passing in the "Stinger".
The "Stingers"
are activated by four functions: "Extend",
"Retract", "Seal energize" and "Seal de energize". The two first
respectively serve to make them go down in the receptacle female of the LMRP or
the "Stack" and go up in
the receptacles of the POD (parking position for lifting for example). The
"Seals" are mobile joints
which make it possible to ensure the sealing of the lines between the "Stinger" and the receptacle female.
They ensure the sealing of the lines during the tests when the "Stingers" are in parking mode
(Retract) and the "Seals"
energized or under normal operation: "Extend"
and "Seals" energized. When
the "Stingers" are inserted
in the receptacle female of the LMRP or the "Stack", they ensure the passage of the fluid between the POD
and the elements of the LMRP or the "Stack".
These joints must be energized before launching any order passing by the "Stingers".
The "Stingers"
must be handled with precaution in particular when one uses the PETU test unit
because it does not always contain the Interlock between functions, making it
possible to avoid the human errors. Before activating the functions "Extend" or "Retract", the "Seals" must be de energized and
there must be no pressure in the lines. In the contrary case one is extremely
likely to damage the seals. The functions of the panels include an interlock
which prevents from activating these functions if the "Stinger" is
not in the correct state.- The solenoids
valves:
The solenoids valve of the POD includes an electric part and a
hydraulic part. The electric part is made of a connector with 4 studs (2 for
each coil) and a centring stud connected to a subsea cable attached to the body
of the solenoid. The hydraulic part is ordered by activation of at least one of the coils. During
maintenances and especially during the replacement of the coils or a "Pie connector" of the SEM, the
polarity on the two coils of the solenoids must be checked in order to make
sure that the plunger functions well when the two reels are fed at the same
time. It is the normal operation.
The solenoids valves used
in the POD are not fed by a
D.C. current but by pulses of well defined form. The objective of
this type of order is to decrease the consumption of the system.
It can happen that an output does not function correctly and that
these signals are disturbed. This is why it is interesting to have the general
shape of the signal. Even if one can obtain it by comparison with a solenoid
that is
functioning. The first graph below represents
the general shapeof the
signal with trains
of pulses of
7s and intervals 0,4s at
24V. The second represents the detail of the train of impulse with pulses of
10ms at 24V and 20ms with 0v
With the drafting of
this document, there are two types of solenoids of reference 223290-15 and
223290-63. The -15 are old models and were replaced by -63. The resistance of
the reel of the -15 is about 46-47ohm and that of the -63 is about 41-42ohm
according to whether we measure the coil with or without the connector. The
solenoids -63 B01 revision have a better resistance to penetration of water.
The average consumption of power of a solenoid -63 is about 6W. There are also
various types of cables but the last versions are marked with the reference
4-N-5. This new type is supposed to have a better resistance to the marine
environment and a longer live timeIn order to test the
solenoids, it can be put in a hyperbaric chamber having a pie connector inside
and accessible from the outside. One installs from one to 6 solenoids inside
the chamber, one closes it and one puts the pressure at 250bar during 6 hours.
The connectors not used must be plugged by blind connectors. Then, one can measure
insulations of the coils between them or with the ground. Before measurements,
one makes sure that the "Pie
connector" has a good insulation. It is considered that the solenoid
valve is good when all the insulations are > 20Mohm. On the other hand one cannot check the operation of the hydraulic part of the solenoid in
pressure. Measurement must preferably be made before the test, in the middle of
the test, at the end and after the solenoid was dried after its exit from the
hyperbaric chamber.When the test is
done "dry", the insulation must be >200Mohm.
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The electric connector of the SEM:
The electric connector Nautilus of ODI being on the POD is
connectable under water and is making it possible to connect to the one of the
LMRP. The connector of the POD is a male which connects itself on the female
part of the LMRP. This part female is installed on springs to allow centring
when the POD is reinstalled on its site.
One must shut down the SEM before connecting the
connector for two reasons. First is that the connector is not made for a
connection under tension. The second is related to the inductive character of
the umbilical. A connection under tension would be likely to damage the modems
ROV panel (Remote Operated Vehicule) is an element of the BOP which can be on the "Stack" or the LMRP. It makes it
possible to activate functions of the BOP and to a certain extent to supply it
in hydraulic power from a ROV. It is about an element of last help when one
lost the complete control of the BOP. It is complementary to acoustics but
requires that a ROV can go down at the level from the BOP. That cannot always
be the case if water is saturated with gas.
ROV is also used for the connection of the BOP to the well heads as
it can supply visual indications to the DPo of the ships so that they can move it in the right
directions. For that the ROV is equipped with cameras, acoustic radars and
gyrocompass.
Panel ROV consists of valves or taps of pressure (Stabs) making it possible to feed the
BOP in the event of complete power loss.
It is also equipped with handles so that the ROV can be maintained in position
whatever is the current using one of its arms while it actuates the functions
with the other.
The principal functions activated by the ROV are those making it
possible to recover the "Stack"
or the LMRP but also to close a well with "Shear ram" to cut a drill string or a "Ram" to be closed around a drill
string and if required to make circulate mud.
The ROV is equipped with arm manipulators and
tools making it possible to activate valves or to connect the "Stabs" making it possible to supply
the equipment in hydraulic power. All these tools have a special form adapted
to the shape of the fingers or tools used
Note: One can also in certain cases have a panel ROV on the POD
itself. In this case, it makes it possible to reanimate the POD when this one
lost its power. It can be the case when one descended a recoverable POD (POD
retrievable) or when there is not "Hot
Line".
When a POD does not contain hydraulic fluid under pressure, it
cannot go back on the way without an external action. Indeed, even if the
electric parts function, there is no fluid under pressure to open the valves of
arrival of fluid in the POD. It is thus necessary to provide him a source of
supply of pressure on the pilot circuit to open the normal valves of piloting
and those of power thereafter. The pilot circuit is described in the drawing.
The principle is to feed the pilot circuit of the POD by an external
line in 205bar. When the accumulator of 20L of the POD is charged, one can
start to activate "Riser Stringer"
in order to be able to recover the hydraulic power by the normal circuit. One
starts with a "Deenergise"
of "Riser Stinger" followed
by an "Extend" and an
"Energize". In this
position, the circuit is established but it is still necessary to open the
valves of piloting. One then opens "Solenoid
Supply" to obtain the pressure of 205bar coming from the "Conduit line". It is by this
control that the hydraulic fluid under pressure arrives on PODs. When the
"Solenoid supply" is fed,
one can open the "POD supply"
to provide the 340bar to the power functions power.
The accumulator of the POD serves as a backup reserve of pressurized
fluid that can be used for example when we have retracted the
"Stingers". In this case, they contain enough pressurized fluid to
put them back in place and re-establish the circuits.
The connectors of the subsea cable used by Cameron are of
manufacturers Seacon or ODI. The Seacon connectors are of type PBOF (Pressure Balanced Oil Filled) that wants to say that they are filled with silicone oil
(Oil Filled) and that the internal pressure is equal to that of outside
(Pressure Balanced). This type of technology is avoids having a differential
pressure between the interior and the outside of the cable. That would impose
an extremely resistant structure when one works with the great depths of water
(the hydrostatic pressure increases of 10bar/100m). On the old connectors,
there was a piston which made it
possible to fill the electric connection part with oil coming from the body in
order to equalize the pressure. In the new ones, the pressure is not equalized
and only the body is pressure compensated. One must regularly check the
insulation of these cables, the seals and for the old type their oil level in
particular when they are disconnected many times. The repair of these cables is
not possible on board.
Connectors ODI are of Nautilus type known as "Wet-Mate". That wants to say that one can connect them under water at the pressure of operation but not under tension. Only the female part is compensated in pressure
The body of the two types of cables is a plastic polyurethane tube
covered most of the time by metallic armour. It does not need to resist the
outside pressure since oil inside is with the same pressure. Resistance is
necessary only at the beginning of the diving before the pressures are not
equalized between the interior and the outside of the cable.
The RCB.
The RCB (Riser Control Box) Blue and
Yellow (also noted respectively I and II) are containers under subsea container
comprising several plugs connected to various sensors of the BOP. They contain
a universal controller and two power supply 230V/24V. Each power supply is
provided in power by a different UPS - A or B - coming from the RMJB (or SEM on
other BOP).
The following sensors
are connected on the RCB:
1) The flow meter: It provides 24V pulses. The RCB provides
the 24V power supply.
2)
The inclinometer: It provides values
0-20mA. The RCB provides the 24V power
supply.
3) The temperature
and pressure sensor: It provides two values 4-20mA, one for the pressures and
the other for the temperature. The RCB provides the 24V power supply. It should
be noted that each RCB is connected to a different sensor. The RCB Blue is
connected to the sensor of the "Choke
line" and Yellow to the "Kill
line". On some BOP there is only one
sensor.
4) The proximity sensor which provides
a contact activated at the time of the disconnection of the LMRP.
5)
The connection to the opposed RCB with which one
communicates in RS485. The signals are similar to a Profibus signal. Some BOP
has only one RCB.
6)
The RMJB (or SEJB) with through which one
communicates in RS485 with the SEM which is then given the responsibility to
communicate information towards surface.
In each RCB, the universal controller recovers the analogical states
of the sensors which are connected there but also the values of the other RCB
by the intermediary of a connection RS485. These states are then transmitted
towards the SEM which repeats it towards the equipment of surface via the
umbilical. Each SEM recovers also the values of the opposite RCB and thus the
corresponding measurements. This configuration makes that one can lose the
communication with one SEM and continue to receive the measurement from the
opposite side. This is not true if we lose the two power supply of one POD
because they also supply the RCB of the corresponding colour. The redundancy
exists only at the level of one POD but not for both.
The most significant
values are the pressures which make it possible to control the well. When they
are two, the RCB are not interchangeable. On the one hand on the level of the
external connector but also on the level of the controllers who are different.
Each RCB has a hard identifier Blue and Yellow hard coded into the
microcontroller. Blue is the Master of the communication and Yellow the slave.
When they communicate together, it is always on the initiative of Blue.
Note: On
"Pride Africa" the RCB contains the inclinometer of the risers and
must thus be located at the top of "Flex Joint".
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Note: On PSP, there is only one RCB on which are connected the two SEM, the inclinometer of the risers, the two flow meters of the PODs and the measurement of pressure on the level of the wellhead.
The RMJB.
The RMJB (Riser Mounted Junction Box) is simply a subsea passive
junction container whose functions are
as follows:
-
To ensure the connection of the connector of the
umbilical.
-
Distribution of the power coming from UPS A and B
towards the RCB and the SEM.
-
Distribution of the signals of the RCB towards the
SEM and the SEM towards the two DU on the surface.
Note: On the PAN
it includes also a fibre optic converter RS485 and video for particular
applications (positioning by Sonardyne RovNav or under water camera).
Note: On other
units, the umbilical is not directly connected on the RMJB but to an
intermediate connector and then to another kind of container called SEJB (Subsea Electronic Junction Box). Its function is the same.
Electric inclinometer:
The inclinometer is a simple container equipped with an electrical
subsea connector and containing an inclinometer. It is placed at the top of the
flex- joint in order to provide the inclination of the risers on axes X and Y
of the BOP. X is directed positive towards the "Kill line" of the BOP which is directed towards the forward of
the ship.
The inclinometers have two markings (X and Y) making it possible to
direct them in the good position compared to the reference X axis. X is directed
towards the forward of the ship, also named "Bow" or "FWD".
The axis Y is directed towards "Portside"
or "PS". One supposes in this case that the plug is directed
downwards. It is advisable during the assembly to test these angles and to
check that they correspond well with those needed by the systems and
if they vary in the good direction.
When one is on a dynamic positioning drill ship, the inclinometers
of the
Figure 71
Inclinometer.
risers are used in conjunction with that being in the STM of the POD
to inform the operators of positioning (Dynamic
Positioning Operators or DPO) on the
values of angles of the BOP and the risers. From the inclinometers we get the
axes X and Y of the BOP compared to the vertical but also of those of the
risers and thus of the relative differences between the two. A calibration is
carried out by the DPO at the time of the descent of the BOP. One waits until
the BOP is located at approximately 500m of water depth or half way and one
make a set of measurements by supposing that it hangs vertically. The result
provides the variations of assembly compared to the supposed vertical.
Calculations must be carried out on an average of let us say ten measurements
and to make it possible to obtain almost null variations at the end.
On the anchored
units, the values of inclination are visible only on the Event Logger. In this
case, there is no simple way to rectify
the initial alignment errors of the axes during
the assembly except
to modify the software of BOP panels.
The electric inclinometers are connected each to one of the RCB Blue
and Yellow which provides them the 24VDC supply. It provides a signal 0-20mA
for values of angles of +-14.5 degree. The output value of RCB is between
-32768 to 32768.
In parallel with the electric inclinometers, there are also two
acoustic inclinometers. One is located on the LMRP and the other at the top of
the "Flex-joint". In
certain cases, one can also find one on the level of the "Risers". These inclinometers have
the same functions as the electric ones but they are generally used as backups.
The acoustic signals are received by a unit of reception located on the hull
and treated by an acoustic system separated from the BOP Multiplex system of
the BOP.
The principal reason for which one measures these angles is due in
the limitations of the "Flex-joint"
to the level of the BOP (approximately 8°) but not only. There also exist
angular limits in surface at the level of the "Surface Flex-joint", of extension of the "Slip-joint" and those of the riser
compensators.
Note: On PAF, the riser inclinometers are included in the RCB which
must thus be located at the top of the "Flex joint". Note: On PSP or PNA, there is only a riser
because they are anchored platforms.
Flowmeters.
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The LMRP is equipped with a flow meter on each POD. They are
measuring the flow only on the power
part of hydraulics. They consist of a turbine actuated by the flow of the
hydraulic fluid and whose rotation of the blades is detected and transformed
into impulses by a magnetic sensor. The signals are 24V pulses.
The flow meter is
connected directly on
the RCB by the
intermediary of a subsea cable.
The RCB provides
the24V DC to supply
the sensor. The body of the flow meter must be assembled in the direction of
the displacement of the liquid.
The principal function of the flow meter is to measure the volume of
the consumed fluid when a function is activated. The consumption of fluid is
indeed the only proof that a hydraulic function was carried out. Even if the
electronic part does not bring back any error information, this is the only way
to ensure that a function has been activated. During the functional tests, one precisely
Figure 74
Flowmeter on LMRP.
notes volumes
and times of fillings in order to be able to make controls in operation. The
flow meter is also used to detect the leaks in the power circuits.
Temperature & pressure sensors.
The BOP is in general
equipped with sensors of high pressure and temperature at the level of the
lines "Kill" and "Choke".
These sensors are
situated in a container similar to the
one of the pictures. That of the "Kill
line" is on the LMRP and that of the "Choke line" is in the "Stack" and is measuring the pressures and temperatures at the
level of the wellhead before the "Rams".
The sensor of the "Kill line"
is connected on the RCB Yellow and that of the "Choke line" to the RCB Blue.
In term of electric connections, the sensor of the "Kill line" is directly connected on
the RCB which provides the 24VDC supply.
Each sensor provides a signal 4-20mA on a scale of 240°C and 1000bar (the
values provided by the RCB are to be subtracted of 13107). On the other hand
the sensor of the "Choke line"
is connected on the RCB by means of a connector
equipped with a
handle which can be
connected and
disconnected in water. This connector is useful at the time of the
disconnections of the BOP
when one
separates the LMRP from the "Stack".
The "Stack" remains at the
bottom and the LMRP goes up. The connector of the sensor is assembled with
slings to the handle so that it is disconnected during separation.
After the reconnection of the LMRP with the
"Stack", the connector is
reconnected by the ROV by using the handle. This is the function of the handle.At the time of electric disconnection of BOP (EDS), i.e. when one
separates the LMRP from the "Stack"
which remains at the sea-bed, one need to know the moment when the two parts
are separated. This information is useful to control the rising of the LMRP because
of the forces applied to the risers. Indeed, under normal operation, the risers
should not apply a too strong
compressive force to the BOP. This is why in addition to have floats on the
risers; one applies a force to the top named "Over pull" using the compensator (Tensioners). It is about
~40t on the boats but it can be stronger in other cases for example during
drillings in great depths. This force is used to rather maintain the risers in
extension as in compression what would tend to make them bend.
If this force were not controlled, one could see the LMRP going up
quickly and the assembly to follow with the risk to damage the equipment of
surface.
The system of control called "Anti recoil" sends two signals to the system of the
compensator. A signal of "Warning" when the disconnection starts and a "Disconnected" signal when the LMRP
is disconnected to indicate that the control of the increase can start. The
sensor of proximity is activated when the LMRP starts to separate from the
"Stack". It is him which
makes it possible to launch the "Disconnected" message.
The sensor itself is a simple magnetic proximity detector which can
function in great water depth. It consists of a magnetic sensor, a body
containing electronics and a subsea connector. It is placed in order to detect
the presence of one of the studs of centring of the "Stack" on the LMRP. The produced signal is a contact
(polarized).
Note: This system is not used by the acoustic disconnection where it
is replaced by an adjustable temporization. The principle of the system remains
the same one but that make more random the period of control of the rising.
However this system being used as a last resort, one can certainly accept some material
breakages to save the people and the unit.
Acoustique.
We already spoke about acoustics when we described the levels of
redundancy. The acoustic system is located on the "Stack" in the lower part of the BOP. The principal function of
acoustics is to disconnect the BOP but we also have the possibility of ordering
individual functions. This system is made of the following elements:
-
A container of command named "Acoustic SEM" (Subsea Electronic Modulates,
vertical on the picture) supplied with
Lithium or rechargeable batteries. The life time of the batteries must be of
180j at a rate of 100 operations (API16D
in 2005). In fact, the Sonardyne system with 3 years autonomy at a rate of
a test per week and 6 functional tests per year.
-
Two acoustic emitter and receiver, the DART (Deep Acoustic Remote Transducer, horizontal on the image), connected to the container
and assembled on arms which are deployed automatically with the depth. The DART
are two to ensure the redundancy but also to avoid the acoustic zones of
masking when the ship turns around the BOP because there is in general only one
unit of emission on the surface.
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