GB2061723A

GB2061723A - Suppressing fires on offshore oil platforms

Info

Publication number: GB2061723A
Application number: GB8006854A
Authority: GB
Original assignee: Sedco Inc
Current assignee: Sedco Inc
Priority date: 1979-10-29
Filing date: 1980-02-28
Publication date: 1981-05-20
Also published as: NO153285C; NO153285B; GB2061723B; NO150422B; NO150422C; NO802224L; NO802223L

Abstract

An offshore oil platform 10 has mounted on it a stab receptacle 32 connected by pipes to nozzles at a plurality of locations on the platform. A marine service vessel 16 has a stab assembly 30 removably mounted on a crane boom including a hollow stab connected by a flexible pipe 34 to a pump. A method of suppressing fires on the platform comprises manoeuvering the vessel adjacent the platform, inserting and engaging the stab in the receptacle, separating the stab from the stab assembly and supplying fire suppressing fluid through the pipe 34, stab, stab receptacle 32 and pipes to the plurality of locations on the platform. <IMAGE>

Description

SPECIFICATION Suppressing fires on offshore oil platforms This invention relates to fire suppression systems for use with offshore oil platforms and in particular to afluid conducting stab and stab receptacle system for use in conducting a supply of fire suppressing fluid from a service vessel to a platform, and to a method of fire suppression on such platforms.

Rising prices of hydrocarbon energy sources have made the offshore production of hydrocarbons economically attractive. Offshore production accounts for a large percentage of the worldwide oil production and that percentage is expected to increase in the future. The technical problems of providing oil drilling and production platforms in waters approaching 350 metres deep have been rapidly overcome. The cost of building the necessary structures usually can be justified only when a large number of wells are drilled from a single platform.

The term "platform" is in fact somewhat mis-leading since the modern offshore oil platforms often more closely resemble a large multistory factory and hotel complex. While the platforms have been quite massive, space is still at a premium when it is considered that typically ten to fifty wells are drilled from each platform and large quantities of equipment must be provided nearthewellheads during drilling and production. The wellhead locations are therefore usually surrounded by the equipment which, in turn, is housed in numerous compartments into which the multistory platforms are divided. In this specification the term "offshore oil platform" is used to include any type of offshore structure or tethered vessel used in connection with exploration for or recovery of oil and/or natural gas.

While it may appear that the simplest manner of fighting fires on a platform is to provide the fire fighting equipment on the platform itself, this arrangement is not practical for several reasons. In the case of a blowout, it is essential that all power on the platform be shut off immediately to avoid any sparks which might ignite escaping gas. If an explosion or fire has already occurred, damage to the platform is usually so extensive that it would be impossible to keep a power system in operation. Even if some power were available to operate a fire fighting system capable of pumping sufficient quantities of fire fighting fluids to the necessary locations, there would be no manpower available to operate the systems. When a blowout occurs, and in any case when a resulting fire occurs, the first concern is to evacuate the platform to avoid loss of life.As a result, the only means of fighting fires on offshore oil platforms has been from a vessel such as a fire boat or an auxiliary platform set up adjacent to the burning platform. In the case of a blowout and fire at a wellhead, it has been found to be quite difficult to supply fire suppressing fluids, such as water or foam, to the location of the fire. That is, while typical fire boats have the capacity to pump large quantities of water and direct it toward a platform, the platform structure itself deflects essentially all of the water and prevents it from reaching a wellhead fire.

Another problem encountered in wellhead fires is the loss of structural integrity of the platform itself.

The most critical structural elements of the platform are those which connect the platform to the top of the supporting legs. The walls are drilled through the supporting legs so that the wellheads are necessarily positioned above the legs and above the critical structural points. In the case of a blowout and fire, hydrocarbon fluids may flow down through the structure and into or around the supporting legs while burning thereby heating the critical structural elements. If these points in the structure are weakened sufficiently by the heat, the entire platform may collapse with obvious disastrous results. It is therefore very important when fighting platform fires to pump large quantities of water to the structural elements at the point of interconnection with the supporting legs.But it is difficult to direct water from conventional fireboats to this part of the structure since the platform itself covers and surrounds this part of the structure. The fire fighting ships must typically direct the water upward to this lower portion of the platform structure from a fairly close and dangerous position and even then may only be able to cool one side of the support structure since the leg itself shields the opposite side from the spray of cooling water.

Thus, a system for directing large quantities of water to the platform structure at the junction of the structure and supporting legs would be highly desirable to avoid total loss of the structure in the case of blowout and fire.

Accordingly, an object of the present invention is to provide apparatus and a method for efficiently directing large quantities of fire fighting fluids to critical locations on offshore oil platforms.

Another object of the present invention is to provide a fluid distribution system on an offshore platform including means for receiving the fire fighting fluid from an external source and means for directing the fluid to preselected locations on the platform.

Another object of the present invention is to provide apparatus carried on a self-propelled vessel for supplying fire suppressing fluids to a fluid distribution system on an offshore oil platform.

According to one aspect of the present invention there is provided a method of suppressing a fire on an offshore oil platform having mounted on it a stab receptacle having a space therein and means communicating with the space for distributing a fire suppressing fluid to at least one location on the platform, the method including the steps of manoeuvering a service vessel to a position adjacent the platform, the vessel having a stab assembly carrying a hollow stab communicating with means for supplying a fire suppressing fluid, inserting the stab into the stab receptacle and supplying a fire suppressing fluid from the service vessel through the stab to the location on the platform. The method preferably includes the step of separating the stab from the stab assembly after its insertion into the stab receptacle and preferably prior to supplying the fire suppressing fluid.

According to a further aspect of the invention an offshore oil platform has a stab receptacle with a space therein, adapted to receive a hollow stab car ried on a service vessel, means to guide the stab into the receptacle and means connected to the recepta cle to distribute fire suppressing fluid to at least one location on the platform, whereby fire suppressing fluid supplied from the service vessel through the stab will be distributed to the said locations. The receptacle preferably includes a manifold connected to the means for distributing fire suppressing fluid and means for securing the stab within the receptacle.

According to a still further aspect of the invention a service vessel for use in suppressing fires on such a platform has means to maintain itself at a predetermined position with respect to the platform, a stab assembly including a hollow stab adapted to engage the stab receptacle on the platform and means for controlling the movement of the stab and means for supplying a fire suppressing fluid to the stab under pressure and thus, in use, to the location or locations on the platform. In one embodiment the means for controlling the movement of the stab comprises a pivotally mounted control arm, an actuator operably connected to the control arm and an extension arm mounted on the control arm for translation with respect thereto and carrying the stab.Preferably the means for maintaining the position of the vessel includes an anchor, tension means connecting the anchor to the vessel, means for selectively deploying the anchor and means for determining the distance between the vessel and the platform.

The invention also embraces a stab assembly for such a vessel.

Further features and details of the invention will be apparent from following description of one specific embodiment which is given by way of example with reference to the accompanying drawings in which: Figures 1, 2 and 3 illustrate sequentially the connection of a stab assembly carried on a service vessel to a receptacle on an offshore oil platform; Figure 4 is a more detailed and partially broken away illustration of an offshore oil platform and a stab assembly carried on a boom; Figures 5 and 6 illustrate the details of the stab assembly control mechanism carried on the end of a crane boom; Figures 7 and 8 are cross sectional illustrations of the interconnection of two embodiments of stab assemblies and their respective receptacles; and Figure 9 is a detailed cross sectional illustration of a split ring assembly for securing a stab assembly to a receptacle.

The general apparatus and method of the present invention is illustrated sequentially in Figures 1 to 3.

A simplified illustration of an offshore oil platform is illustrated at 10 supported in legs 12. Flames 14 indicate that a blowout and fire has occurred in a well drilled through one of the legs 12. As noted above, in case of such a fire, all systems on the platform 10 are shutdown and all personnel are evacuated so that fire fighting must be done from another work platform such as a semi-submersible service vessel 16.

The vessel 16 is of generally conventional construction having an overall length of about 140 metres, a width of about 75 metres and a height from its lower hull 18 to its deck 20 of about 45 metres.

The vessel 16 is preferably modified so that the hulls 18 do not extend beyond its forward vertical column 22. This modification allows the vessel 16 to approach an offshore platform very closely without fear of collision between the lower hull 18 and a platform leg 12. A crane 24 of the 250 to the 350 ton class is carried on the forward end of the vessel 16 and has a boom 26 which may be extended from the forward end of the vessel 16 to provide a very long and safe reach of up to 100 metres from the forward end of the vessel. The vessel 16 also preferably carries a modular arrangement 28 having crew quarters, infirmary and fire fighting equipment including pumps on the work deck 20.

The vessel 16 includes a number of elements which together allow the vessel to be maintained very accurately at a selected position relative to the platform 10. These include at least a pair of mooring lines 36 connected to retrieval means, or winches 38.

A main propulsion system 40 is provided for moving the vessel to its work location and also for use in dynamic positioning. Side thrusters (not illustrated) are also preferably included on the vessel for dynamic positioning. In addition, a sonarunit41 is provided for determining the distance between the forward end of the vessel 16 and the platform 10.

With the output from sonar unit 41, or some other distance measuring equipment, the positioning of vessel 16 may be automated. This positioning equipment is employed to bring the vessel 16 into close proximity with the platform 10 as illustrated in Figures 1 and 2 and to maintain it there, without danger of collision.

Once the vessel has been brought into position as illustrated in Figure 2, fire fighting equipment on the vessel 16 is coupled to critical locations on the platform 10 by means of a stab assembly 30 including a stab 56 carried on the end of the boom 26 and a receptacle arrangement 32 carried on the platform 10. Aflexible hose 34extends from the stab 56to pumping equipment and a source offire suppressant fluid on the work deck 20. The assembly 30 includes positioning apparatus for aligning it with the receptacle 32 and for inserting the stab into a locked position within a receptacle socket as illustrated in Figure 2. After the stab has been locked into the receptacle 32, the positioning apparatus is pulled free from the stab itself leaving the stab locked to the receptacle 32, as shown in Figure 3. The crane boom 26 may then be moved away from the platform 10 and, if desired, the vessel 16 may move away within the constraints imposed by the length of the hose 3'4.

The hose 34 may be released from the crane boom 26 so that the crane 24 may be used for other operate tions including the connection of other stabs into other receptacles on the platform 10.

While the vessel 16 has been illustrated as a conventional semi-submersible, other types of vessels may also be used. A conventional drillship or service vessel could carry the necessary equipment and the crane 24 and could possibly reach the scene of a fire more quickly. In appropriate circumstances, the equipment may be positioned on an adjacent platform. A semi-submersible is preferred since it provides a large stable work platform and can be moved fairly rapidly.

With reference now to Figure 4, details of the invention are illustrated in a broken-away view of lower levels of the platform 10 and the end of the boom 26 carrying the stab assembly 30. Modern platforms 10 generally are constructed in the form of a number of compartments 42 each housing and protecting various type of equipment. The wellheads 44 are located within compartments directly over the legs 12 through which the wells are drilled. As illustrated, each of the wellhead compartments is surrounded by other compartments filled with necessary equipment which block access to the wellhead site. One or more of the stab receptacles 32 are provided in the outer walls of, for example, a compartment 46.A piping system 48 connects the receptacle 32 to a number of nozzles 50 which are positioned to direct fire suppressing fluid on critical areas such as the wellhead compartments and the steel structure connecting the platform 10 to the legs 12.

The stab assembly 30 carried on the boom 26 includes a control arm 52, an extension arm 54 and the actual stab element 56, all pivotally carried on the end of the boom 26. Hydraulic cylinders 58 control the position of the assembly 30 to place it in alignment with the receptacle 32 so that the extension arm 54 may drive the stab 56 into its locking position within the receptacle. The flexible hose 34 is connected to the stab 56 to conduct fluid flow from the vessel 16.

Figures 5 and 6 provide two views of the directional control arrangements provided in the stab assembly 30. As illustrated, the control arm 52 comprises an actuator in the form of a hydraulic cylinder pivotally connected to the end of the boom 26 by a universal joint 60. The small hydraulic cylinders 58 control the horizontal and vertical directions of the control arm 52 as indicated in Figures 5 and 6, respectively. The extension arm 54 is integral with a piston carried within the cylinder 52 and carries on its extended end the stab 56.

Reference to Figure 7 provides more details of the method of connecting the stab 56 to the extension arm 54. In particular, a recess or socket 62 is provided in the stab 56 for receiving the end of the extension arm 54. In addition, shear pins 64 are provided in the end of the extension arm 54 and in the stab 56 for connecting the stab to the extension arm.

When the stab 56 is locked into the receptacle 32 and the extension arm 54 is retracted, the extension arm is separated from the stab 56 by shearing off the pins.

Further reference to Figure 7 shows that the stab receptacle 32 comprises a cylindrical socket section 66 and a conical guide way 68. The cylindrical section 66 is carried mostly inside the compartment 46 and is attached to an outer wall 70 of the compartment. A locking groove arrangement 72 is provided on an inner wall of the cylindrical section 66 for receiving a locking ring carried by the stab 56, further details of which are explained with reference to Figure 9 below. Rubber gaskets 74 may be provided on the outer surface of the stab 56 to provide a watertight seal between the receptacle 32 and the stab 56. In the embodiment shown in Figure 7, a single main conduit 76 is coupled to the inner side of the receptacle 32 to direct water to desired locations.

Branch conduits 78 may be provided leading from the main conduit 76 to the various locations where fire suppressing fluid is required. In a preferred embodiment, the hose 34 leading from the vessel 16 to the stab 56 has an outer diameter of 30 cm. The stab 56 itself also has an outer diameter of 30 cm and provides a fairly close fit with the inner surface ofthe cylindrical portion 66 of the receptacle 32. In the preferred form, the largest diameter portion of the conical guide 68 is about 250 cm. The conduit 76 preferably has an outer diameter of at least 25 cm. These pipe sizes are intended to carry the large quantities of fire suppressing fluids required, typically 35 to 150 thousand litres per minute.

With reference to Figure 8, a modified stab and receptacle arrangement is illustrated which allows for selection of which areas are to receive fire suppressing fluid. Portions of a receptacle 80 and stab 82 external to a wall 70 may be identical to those portions illustrated in Figure 7. The locking ring arrangements 72 inside the wall 70 may also be identical. But the cylindrical socket portions of the stab 82 and the receptacle 80 step down to provide three different diameters. A first diameter portion 84 of the stab 82 may be of the full cm diameter but it has a side port 86 in communication with a branch conduit 88 leading to a particular fire control area. Similarly, a second and smaller diameter portion 90 of the stab 82 has a side port 92 in communication with a second branch conduit 94.A third and yet smaller diameter section 96 of the stab 82 has a third side port 98 in communication with a branch conduit 100.

A main conduit 102 is in communcation with the central bore of the stab 82. The internal portion of the receptacle 80 is stepped down to match the config oration of the stab 82. A number of rubber seals 104 are provided between the stab 82 and receptacle 80 so that each of the branch conduits is isolated from the others.

The embodiment shown in Figure 8 provides a method of selecting areas to which the fluid will be conducted. In this way, it would be possible to provide a small number of receptacles 80 in the best locations for access from the service vessel 16.

Branch conduits such as conduits 88,94 and 100 may then be provided leading to all of the possible critical locations on the platform. In case of a blowout and fire, it is likely that fire suppressing fluids will be needed only in certain of the critical areas depending on the location of the fire. If the location of the fire, and therefore the critical danger points on the platform, can be located prior to linking the service vessel 16 to the platform by means of the stab 82, the stab may be modified to conduct fluid only to the critical locations. This may be done simply by providing plugs, such as plug 106 which may be inserted into the selected port in the stab 82 prior to connection of the stab to the receptacle. This arrangement can provide the most efficient use of fire fighting equipment which is available.

An alternate method of directing fluid only to criti cal areas our a particularfire location is simply to pro vide a plurality of receptacles as illustrated in Figure 7. For example, a fire at a particular wellhead loca tion can be anticipated to endanger only certain portions of the platform and a separate receptacle 32 can be arranged to conduct fluid to each of those critical locations corresponding to the particular fire condition.

Reference to Figure 9 provides a more detailed illustration of the locking ring arrangement which holds the stab 56 or 82 into the corresponding receptacle socket once it has been driven into place by the service vessel supported equipment. A groove 72 is provided on the inner surface ofthe cylindrical section 66 of the receptacle 32. A split or other form of expanding ring 108 is carried in a groove 110 on the outer surface of the stab 56. Upon insertion of the stab into the guide 68, the ring 108 is compressed until the stab is fully inserted in the socket at which point it expands into the groove 72 locking the stab to the receptacle. A cap screw 112 is provided on the outer surface of the cylindrical section 66 for driving the split ring 108 from the groove 72 to release the stab 56 from the receptacle 32.

The use of the present invention is illustrated in Figures 1 to 3. Upon the occurrence of a fire 14 on an offshore platform 10, the vessel 16 is brought to the location as rapidly as possible. During the trip to the location, the stab assembly 30 and the conduit 34 are assembled on the boom 26 of the crane 24. Upon arrival on location, the vessel 16 drops anchors at an appropriate distance from the platform and uses its mooring lines 36 and its propulsion units to approach the platform 10 in a closely controlled manner. Before reaching the location, the crew of the vessel 16 will have been informed of the location of the fire on the platform and can therefore determine the proper approach direction and the appropriate receptacles 32 which may be used to direct the fire suppressing fluids to the critical locations.If the embodiment shown in Figure 8 is employed, the appropriate side part or ports will be plugged in the stab 82 prior to its installation on the boom 26. The boom and stab control apparatus are then brought into alignment with the proper receptacle 32 and the stab is locked into place. As shown in Figure 3, the control apparatus and the boom are then disen- gaged from the stab but the pumping of fire suppressing fluid may being immediately.

While the above description is made assuming that the fire danger involves an actual blowout and wellhead fire, this fire control apparatus may be used in other cases also. For example, a fire may occur in an engine room or any other equipment compartment or module on the platform. It may be desired in such a case merely to flood the appropriate compartment with fire suppressing foam rather than pumping the large quantities of water normally used to cool the structure in a wellhead area in case of a blowout. The present equipment is equally adapted to use with fire suppressing foam or other fluids in place of water. Even in the case of a well head fire, it may be desirable to flood compartments surrounding the fire location with the foam by the use of one stab receptacle while a second is used to flood the actual fire location with, for example, water.

Claims

1. A method of suppressing a fire on an offshore oil platform having mounted on it a stab receptacle having a space therein and means communicating with the space for distributing a fire suppressing fluid to at least one location on the platform, the method including the steps of manoeuvering a service vessel to a position adjacent the platform, the vessel having a stab assembly carrying a hollow stab communicating with means for supplying a fire suppressing fluid, inserting the stab into the stab receptacle and supplying a fire suppressing fluid from the service vessel through the stab to the location on the platform.

2. A method as claimed in Claim 1 which includes the step of separating the stab from the stab assembly after its insertion into the stab receptacle.

3. A method as claimed in Claim 1 or Claim 2 in which the service vessel has a crane with a boom and which includes the step of attaching the stab assembly to the boom.

4. A method as claimed in any one of the preceding claims in which the stab receptable has a plurality of outlets each communicating with a respective location on the platform and the stab has a plurality of discharge ports each of which communicates with a respective outlet when the stab is inserted in the stab receptacle, which includes the step of blocking at least one of the ports in the stab to select the locations to which the fire suppressing fluid is supplied.

5. A method of suppressing a fire on an offshore oil platform substantially as specifically herein described with reference to Figures 1 to 6 and 9 in conjunction with either of Figures 7 and 8.

6. An offshore oil platform having a stab receptacle with a space therein adapted to receive a hollow stab carried on a service vessel, means to guide the stab into the receptacle and means connected to the receptacle to distribute fire suppressing fluid to at least one I'ocation on the platform, whereby fire suppressing fluid supplied from the service vessel th roug h.the stab will be distributed to the said locations.

7. A platform as claimed in Claim 6 in which the receptacle includes a manifold connected to the means for distributing fire suppressing fluid and means for securing the stab within the receptacle.

8. A platform as claimed in Claim 7 in which the manifold has a plurality of ports each connected to means to distribute fire suppressing fluid to a differ- ent location on the platform and each being adapted to communicate with a respective port in the stab when the stab is within the receptacle.

9. A platform as claimed in any one of Claims 6 to 8 in which the means for distributing fire suppressing fluid includes a nozzle located near to the or each location on the platform, and a distribution line connecting the or each nozzle to the receptacle.

10. A platform as claimed in any one of Claims 6 to 9 in which the receptacle is mounted in a wall which partially defines a compartment on the plat form.

11. A platform as claimed in any one of Claims 6 to 10 in which the guide means includes an outwardly divergent funnel shaped guide.

12. An offshore oil platform substantially as specifically herein described with reference to Fig ures 1 to 4 and 9 in conjunction with either of Figures 7 and 8.

13. A service vessel for use in suppressing fires on an offshore oil platform as claimed in any one of Claims 6 to 12 having means to maintain itself at a predetermined position with respect to the platform, a stab assembly including a hollow stab adapted to engage the stab receptacle on the platform and means for controlling the movement of the stab and means for supplying a fire suppressing fluid to the stab under pressure and thus, in use, to the location or locations on the platform.

14. A vessel as claimed in Claim 13 in which the stab is removably mounted on the stab assembly.

15. Avessel as claimed in Claim 13 or Claim 14 in which the stab has a plurality of outlet ports and means for closing at least one of the ports.

16. A vessel as claimed in Claim 15 in which the means for closing comprises a plug adapted to fit into the said outlet port to block it.

17. A vessel as claimed in any one of Claims 13 to 16 in which the means for controlling the movement of the stab comprises a pivotally mounted control arm, an actuator operably connected to the control arm and an extension arm mounted on the control arm for translation with respect thereto and carrying the stab.

18. A vessel as claimed in any one of Claims 13 to 17 in which the stab assembly is carried by a boom adapted to be mounted on a crane.

19. Avessel as claimed in any one of Claims 13 to 18 in which the means for supplying the fire suppressing fluid comprises a flexible hose connecting the stab to a pump.

20. A vessel as claimed in any one of Claims 13 to 19 in which the means for maintaining the position of the vessel includes an anchor, tension means connecting the anchor to the vessel, means forselec- tively deploying the anchor and means for determining the distance between the vessel and the platform.

21. A service vessel for use in suppressing fires on an offshore oil platform substantially as specifically herein described with reference to Figures 1 to 6 and 9 in conjunction with either of Figures 7 and 8.

22. A stab assembly for a service vessel as claimed in Claim 13 including a hollow stab adapted to engage a stab receptacle on an offshore oil platform, means for controlling the movement of the stab and means for supplying fire suppressing fluid to the stab under pressure.

23. An assembly as claimed in Claim 22 in which the stab is removably mounted on the stab assembly.

24. An assembly as claimed in Claim 22 or Claim 23 in which the stab has a plurality of outlet ports and means for closing at least one of the ports.

25. An assembly as claimed in Claim 24 in which the means for closing comprises a plug adapted to fit into the said outlet port to block it.

26. An assembly as claimed in any one of Claims 22 to 25 in which the means for controlling the movement of the stab comprises a pivotally mounted control arm, an actuator operably connected to the control arm and an extension arm mounted on the control arm for translation with respect thereto and carrying the stab.

27. An assembly as claimed in any one of Claims 22 to 26 in which the means for supplying the fire suppressing fluid comprises a flexible hose connecting the stab to a pump.

28. An assembly as claimed in any one of Claims 22 to 27 including a boom attachment adapted to be mounted on a crane boom.

29. A stab assembly for a service vessel for use in suppressing fires on an offshore oil platform substantially as specifically herein described with reference to Figures 1 to 6 and 9 in conjunction with either of Figure 7 and Figure 8.