System and Method for Rescuing a Malfunctioning Subsea Blowout Preventer

Abstract

A pair of rescue vehicles are deployed on deployment cables to force the shear ram of a sub-sea BOP to shut if it should malfunction. The rescue vehicles may be provided with a camera for remote operation from the surface. The rescue vehicles include securing arms to mate with receiving means on the BOP or its enclosure. The securing arms actuate hydraulic means to release the BOP shear ram piston from hydraulic lock. The rescue vehicles carry their own hydraulic fluid under pressure, or hydraulic fluid pressure may be supplied from the surface or from an ROV, in order to actuate a rod which strikes the accessible BOP shear ram tail rod, forcing the shear ram shut. The rescue vehicles also carry their own securing wedges to slide down behind the vehicle rod, securely holding the BOP shear ram shut.

Description

FIELD OF THE INVENTION

The present invention relates generally to the field of sub-sea blowout preventers and, more particularly, to a system and a method for assisting the shutting of such a blowout preventer should it fail to properly shut.

BACKGROUND OF THE INVENTION

A blowout preventer (BOP) for deep subsea oil and/or gas well work is commonly hydraulically operated. The hydraulic pressure may be electrically generated downhole or provided from a surface source. Commonly used hydraulic control valves require electrical power to actuate. The signal for actuation may be by way of a hard wire, an acoustic signal, or by radio frequency signal transmission. Failure of any of (1) power to supply the hydraulic pressure, (2) the signal circuit, (3) any of several control valves, or (4) leakage of hydraulic fluid supply will render the BOP inoperative.

Such a BOP is provided for subsea drilling operations which may experience a blowout, i.e. an uncontrolled flow of formation fluids into the drilling well. A blowout can cause loss of life, pollution, damage to drilling equipment, and loss of well production. In the event of a blowout, a shear ram within the BOP is designed to rapidly shear the drill pipe and thus shut off the well. The BOP also includes monitoring equipment to indicate to operators on the surface the status of the various rams of the BOP, including the shear rams.

A riser pipe carries formation fluids from the BOP at the sea floor to a surface drilling vessel and circulates drilling fluids down through a drill bit at the bottom of the drill string. The marine riser pipe connects to the BOP through the lower marine riser package (“LMRP”), which contains a device to connect to the BOP, an annular seal for well control, and flow control devices to supply hydraulic fluids for the operation of the BOP. Many BOP functions are hydraulically controlled, with piping attached to the riser supplying hydraulic fluids and other well control fluids. In deeper water installations, other functions as electrically controlled, with a battery on the BOP providing DC electricity for these functions. Typically, a central control unit allows an operator to monitor and control the BOP functions from the surface. An operator aboard a surface vessel typically operates the flow control components and the BOP functions via an electronic multiplex control system.

Certain drilling or environmental situations require an operator to disconnect the LMRP from the BOP and retrieve the riser and LMRP to the surface vessel. The BOP functions must contain the well when a LMRP is disconnected so that formation fluids do not escape into the environment. To increase the likelihood that a well will be contained in an upset or disconnect condition, companies typically include redundant systems designed to prevent loss of control if one control component fails. Usually, companies provide redundancy by installing multiple independent central control units to back up all critical control units. Only one control unit is used at a time, with the other providing backup.

In U.S. Pat. No. 7,757,772, Donohue et al. proposed a system and method to allow backup or alternate fluid flow routes around malfunctioning components using removable, modular component sets. The system and method of Donohue et al. were directed to providing operational redundancy, in contrast to safety redundancy, which has been focus of most prior art systems. In one embodiment in Donohue et al., an ROV establishes a backup hydraulic flow to a BOP function by attaching one end of a hose to a modular valve block and the other end to an intervention shuttle valve, thus circumventing and isolating malfunctioning components. A compound intervention shuttle valve is provided that comprises first and second primary inlets, first and second secondary inlets, and an outlet. A modular valve block is provided that comprises a directional control valve, a pilot valve, a manifold pressure regulator, a pilot pressure regulator, stab type hydraulic connections and an electrical wet-make connection.

While the system proposed by Donohue et al. does indeed provided additional operational redundancy, it is not effective in shutting a malfunctioning shear ram if the problem is not of the type requiring hydraulic backup. For example, if the hydraulic system is still intact, but the shear ram failed to shut because it was jammed or otherwise failed to shut, then the system of Donohue et al. would be ineffective. Thus, there remains a need for a simple, robust system to provide a rescue shutting force to a shear ram in the event of a failure. The present invention is directed to filling that need in the art.

SUMMARY OF THE INVENTION

The present invention addresses these and other needs in the sub-sea blowout preventer art by providing a pair of BOP rescue vehicles. Before the BOP is deployed to the sea bottom, it is modified so as to be ready to receive the rescue vehicles. First, the tail rods of the shear rams are made accessible outside the BOP body, if they are not already accessible by design. The rescue system of this invention is equally applicable to other types of BOP rams. Second, means is provided to mechanically receive the rescue vehicles and securely hold the vehicles to the BOP for operation. This receiving means may alternatively be provided on the lower marine riser package. And third, a five-way valve is provided to isolate the primary hydraulic system and to bypass the BOP's shear ram piston so that it is not hydraulically locked and can be made to shut by external means provided by the rescue vehicles.

The rescue vehicles are deployed on deployment cables, and may be provided with a camera for remote operation from the surface. The rescue vehicles include securing arms to mate with the receiving means which were a part of the modification of the BOP. The securing arms actuate the hydraulic five-way valve to release the BOP shear ram piston from hydraulic lock. The rescue vehicles may carry their own hydraulic fluid under pressure in order to actuate a rod which strikes the accessible BOP shear ram tail rod, forcing the shear ram shut. Alternatively, a battery powered pump may be installed on the BOP, to be activated by the rescue vehicles, a stab-in connection may provide hydraulic pressure from the surface or from the rescue vehicles, or other pressure sources may be provided. The rescue vehicles also carry their own securing wedges to slide down behind the vehicle rod, securely holding the BOP shear ram shut.

These and other features and objects will be readily apparent to those of skill in the art from a review of the following detailed description, along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a side schematic view of a shear ram portion of a known blowout preventer.

FIG. 2 is a side schematic view of the BOP of FIG. 1 after the shear ram has been actuated.

FIG. 3A is a top view of the BOP of FIG. 1, modified in accordance with the teachings of the present invention to include a rescue vehicle and structure.

FIG. 3B is a side schematic view of the BOP of FIG. 1 with the addition of a rescue vehicle in place, in accordance with the teachings of the present invention.

FIG. 4A is a top view of the modified BOP of FIG. 3A.

FIG. 4B is a side schematic view of the BOP of FIG. 3B after the shear ram has been assisted in actuating by the present invention.

FIG. 5A is a top view of a BOP with a pair of rescue vehicles deployed to assist in shear ram closure.

FIG. 5B is a side elevation view of the BOP and pair of rescue vehicles of FIG. 5A.

FIG. 6A is a top view of a BOP with a pair of rescue vehicles in contact with the BOP during deployment.

FIG. 6B is a side elevation view of the BOP and pair of rescue vehicles of FIG. 6A.

FIG. 7A is a top view the BOP of FIG. 6A with the rescue vehicles positioned to assist the shutting of the shear rams of the BOP.

FIG. 7B is a side elevation view of the BOP and rescue vehicles of FIG. 7A.

FIG. 8A is a top view of a type of BOP that does not have an exposed tail rod.

FIG. 8B is a side elevation view of the BOP of FIG. 8A.

FIG. 9A is a top view of the BOP of FIG. 8A, modified to receive the rescue vehicles of the present invention.

FIG. 9B is a side elevation view of the modified BOP of FIG. 9A.

FIG. 10A is a top view of a modified BOP of FIG. 9A.

FIG. 10B is a side schematic view of the BOP of FIG. 9B, with rescue vehicle systems in place to assist shutting the shear rams of the BOP.

FIG. 11A is a top view of an ocean bottom BOP on a lower marine riser package, illustrating the option of rescue vehicle receiving posts mounted in the lower marine riser frame, rather than on the BOP.

FIG. 11B is a side elevation view of the BOP LMRP of FIG. 11A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a schematic drawing of the shear ram portion of a known BOP 20. The

BOP comprises a body 22 including an axial bore 24 arranged along an axis 26. Drill pipe, coiled tubing, or the like (not shown) is run through the bore 24. A pair of bores 28 extend laterally from the bore 24 and retain two halves 30 and 32 of a shear ram. The shear ram halves 30 and 32 are each attached to a respective rod 34 which is attached to or integrally formed with a respective piston 36. Each piston is retained within its own cylinder 38. As used herein, the term “ram” alone may represent the two ram halves, whether a shear ram, a slip ram, or other type.

Throughout the following description, it is to be understood that the BOP includes a pair of opposing shear ram halves, and thus substantially identical structure is called for on either side of the BOP, including the structure of the rescue system of the present invention. For example, a structural element may be identified in the singular, where it is to understood that the same structure is called for on the other side of the BOP.

The BOP of FIG. 1 is hydraulically operated. A hydraulic pressure source 40 is coupled to a supply line 42, which passes through a four-way hydraulic control valve 44. A return line 46 return hydraulic fluid to a return reservoir. When the control valve 44 is aligned as shown in FIG. 1, hydraulic fluid pressure is supplied to an open line 50 which ports hydraulic fluid pressure to an inboard side of the pistons 36, tending to move the shear ram halves 30 and 32 out away from the bore 24. If the control valve is re-aligned, then hydraulic fluid pressure is supplied to a shut line 52 which ports hydraulic fluid pressure to an outboard side of the pistons 36, tending to move the shear ram halves 30 and 32 inward toward the bore 24, thereby shearing the drill pipe, coiled tubing, or the like.

Each piston 36 includes a tail rod 54, either attached to the piston or integrally formed with the piston. The tail rod extends through an opening 56 in the body 22 of the BOP so that it is accessible outside the BOP.

The BOP 20 also includes a latching wedge 58 adjacent each tail rod 54. The wedge 58 is operated by a wedge piston 60 which is enclosed within a wedge cylinder 62. An open line 64 is in fluid communication with the open line 50, and ports fluid pressure to a side of the piston 60 which tends to hold the wedge 58 in an open position. A shut line 66 is in fluid communication with the shut line 52 so that porting hydraulic fluid pressure so as to shut the shear ram also ports pressure tending to move the wedge down into a latching position. Once the ram moves in enough to clear the tail rod away from the wedge, the wedge will shut, if everything works as intended.

This is shown in FIG. 2. Under the control of the control valve 44, which has now been shifted (to the right as viewed in FIG. 2) to a control position to shut the shear rams of the BOP, hydraulic fluid pressure is supplied from the pressure source 40 to the shut line 52. Fluid pressure thus moves the pistons 36 inward toward the bore 24. At the same time, fluid pressure is supplied to pistons 60, urging the wedges 58 down behind the tail rods when they have moved out of the way. Note that affirmative action will now be required to move the wedges back out of the way, in order to pull the BOP rams back away from the bore 24.

The action thus described may fail for a number of reasons. Loss of hydraulic fluid and pressure due to any one of the seals or in the pipe and fittings will render the BOP useless. Furthermore, supplying a backup fluid supply will have no effect if additional hydraulic fluid pressure is simply bled off in a leak. In addition, failure of the signal to reach the controller which operates the control valve 44, or failure the 4-way valve itself, will also cause BOP failure. The fail-safe position of the system maintains fluid pressure from the source 40 to keep the BOP rams in the open position.

If the BOP should fail to operate for any of these or other reason, a BOP rescue vehicle 68 of this invention may be employed, as shown in FIGS. 3A and 3B. The BOP rescue system illustrated in FIGS. 3A and 3B is designed to restore full closing function to the BOP to overcome any combination of the problems listed above. This is accomplished by the present invention primarily in two ways. In case the control valve 44 does not function, a means must be available to release the hydraulic pressure from the source 40. For this purpose, a five-way control valve 16 is provided in the open line 50 and the shut line 52. Those of skill in the art will recognize that the BOP of the prior art must be modified to include the control valves 16 before the BOP is installed on the sea floor. In the quiescent position, the valve 16 simply ports whatever pressure in the open shut lines straight through. In the actuated position, as shown in FIG. 3B, a contactor 71 moves the valve to the center position, thereby shutting off both open and shut pressure from the source 40, and bypassing the pistons 36 so that the pistons are free to move without hydraulic lock. In this manner, the hydraulic system of the BOP for operating the shear ram is effectively disabled.

The second way that the shutting of the BOP rams is accomplished involves moving the tail rods 54. For this purpose, an assist open line 72 and an assist shut line 74 are provided in each rescue vehicle 69. Hydraulic fluid pressure is provided by an assist pressure source 76, as shown and described below in relation to FIGS. 5A, 6A, and 7A. The hydraulic coupling for the assist pressure source 76 may also serve to receive hydraulic fluid under pressure from an ROV or through a conduit from the surface. Porting pressure via the assist shut line 74 exerts shutting force on an assist piston 78 and thus an assist rod 80. As the assist rods 80 move in the shut direction, they eventually contact the tail rods 54, which as described above are accessible from outside the body of the BOP. This action of contacting the tail rods 54 is shown in FIG. 4B, where the rams 30 and 32 have been shut. Also shown in FIG. 4B, porting pressure to the assist shut line 74 has also forced an assist wedge piston 82 down, forcing an assist wedge 84 down behind an assist tail rod 86, locking the BOP rams 30 and 32 in the shut position. In this position, the BOP will remain shut with no further assist from the rescue vehicles.

Referring briefly now to FIGS. 3A and 3B, the BOP is shown as modified to accept the rescue vehicles 68. First, the BOP has been modified to include the five-way valve 16, as previously described. The BOP has also been modified to mechanically receive the rescue vehicles 68 by including a pair of posts 88 on each of the starboard and port sides of the BOP, arranged to receive the rescue vehicles. This feature is shown and described below in respect of FIGS. 5B, 6B, and 7B. Further, the posts may be identified as “forward starboard,” “aft starboard”, “forward port”, and “aft port”, referring to its position relative to each rescue vehicle.

Referring now to FIGS. 5A, 5B, 6A, 6B, 7A, and 7B, the presently preferred structure and operation of the rescue vehicle 68 are depicted. Each rescue vehicle is lowered to the BOP by a deployment cable 90, and may be further assisted by coupling to a remotely operated vehicle with a camera and its own propulsion and communication systems to the operator on the surface.

FIG. 5A shows a top-down view of a pair of rescue vehicles 68 approaching a blowout preventer 100. Each rescue vehicle 68 carries a hydraulic fluid source 76 as previously described. A port securing arm 102 and a starboard securing arm 104 extend forward of the rescue vehicles for coupling with the posts 88 of the BOP 100. The arms 102 and 104 terminate in an upwardly depending hook 106 which also defines an upwardly facing contact surface 108. The contact surface 108 is configured to contact and actuate the five-way control valve 16 when the rescue vehicle is mechanically securely in place on the BOP.

Referring now to both FIGS. 5A and 5B, the arms 102 and 104 are spaced apart a predetermined distance d to accommodate the width of the BOP 100. Each of the arms 102 and 104 defines an upwardly facing mating surface 110 to mate in abutting contact with a first of the posts 88, labeled in FIGS. 5A and 5B as 88₁. Each of the arms 102 and 104 also defines a downwardly facing mating detent 112 to mate in abutting contact with a second of the posts 88, labeled in FIGS. 5A and 5B as 88₂.

As previously described, FIG. 5A shows the control valve 16 positioned on the BOP for contact with the upwardly facing contact surface 108. FIG. 5B shows an alternative arrangement. In FIG. 5B, each rescue vehicle includes a contactor 114 arranged so that when the rescue vehicle is mechanically securely in place on the BOP, the contactor 114 comes into abutting contact with the control valve 16, moving the control valve into position for operation of the BOP rescue system described herein.

Referring next to FIGS. 6A and 6B, the rescue vehicles are lowered to make first contact between the arms 102 and 104 and the posts 88₂. From this point, the rescue vehicles are moved forward to the point at which the respective hooks 106 move underneath the respective posts 88₁. Once the hooks 106 pass beyond the posts 88₁, then the upwardly facing mating surface 110 will come into contact with the posts 88₁ mechanically locking the vehicles into place.

The locking of the vehicles into place, ready for operation in accordance with this invention, is shown in FIGS. 7A and 7B. At this stage, the hooks 106 are secured in abutting contact with the posts 88₁ and the detents 112 are in abutting contact with the posts 88₂ and all the weight of the vehicles is supported by the posts. The deployment cables are slack. Also, the contactors 114 have come into contact with and actuated the control valves 16. This action forms a hydraulic fluid path that bypasses the pistons 36 (See FIG. 3B), releasing the hydraulic lock. This action simultaneously bypasses the wedge pistons 60 so that the wedges are not hydraulically locked. Finally, the assist shut lines 74 are pressurized from the on-board hydraulic fluid pressure sources 76 or other pressure source, such as from a remotely operated vehicle or from a surface pressure source, thereby forcing the rods 80 into the tail rods 54. This force is continued until the shear ram is shut and the tubular through the BOP is severed and shut off. As the rods 80 continue forward, the assist wedges 84 slide behind the rods holding the rods 80, and therefore the tail rods 54, in place. No further hydraulic fluid pressure is then called for.

To this point, the system and method of this invention have been described as applied to a BOP in which the tail rod is accessible from outside the body of the BOP. However, some BOP's are made in which the tail rod is not so accessible, with the tail rod within the body of the BOP or enclosed within a tail rod enclosure affixed to the body of the BOP. Such a BOP 200 is shown in FIGS. 8A and 8B. The BOP 200 comprises a body 202 including an axial bore 204 arranged along an axis 206. Drill pipe, coiled tubing, or the like (not shown) is run through the bore 204. A pair of bores 208 extend laterally from the bore 204 and retain two halves 210 and 212 of a shear ram. The shear ram halves 210 and 212 are each attached to a respective assist rod 214 which is attached to or integrally formed with a respective piston 216. Each piston is retained within its own cylinder 218.

The BOP 200 is hydraulically operated in the same manner as previously described in respect of FIG. 1. However, in the BOP of FIG. 8B, each piston 216 includes a tail rod 220, either attached to the piston or integrally formed with the piston. The tail rod 220 extends through an opening 222 in the body 202 of the BOP but is not accessible outside the BOP because it retracts into a cavity 226 within a wedge housing 224. The wedge mechanism works the same as the structure previously described with respect of FIG. 1.

In order to operate with the rescue vehicles as previously described, the BOP 200 must be modified, such as the modification shown in FIGS. 9A and 9B, for example. In this example, the wedge housing 224 now includes a hole 228 which is fitted with an intermediate shaft 230, which is free to move axially. In manner to be described below, the intermediate shafts are forced by the rescue vehicle into the tail rods 220 to shut the shear ram.

The BOP 200 is also modified to include the 5-way valves 16 in the same manner as previously described in respect of FIG. 3B. Finally, the BOP 200 is modified to include the posts 88, in the same manner as previously described in respect of FIG. 5A.

FIGS. 10A and 10B illustrate the operation of the rescue vehicles of this invention with the modified BOP 200. The contactors 114 have been brought into contact with and have operated the control valves 16, thereby bypassing fluid pressure across the pistons, as before. The intermediate shaft is contacted by the assist rods 80 and forced inwardly, thereby shutting the shear ram.

In all previous drawing figures, the BOP body itself has been modified to receive the rescue vehicles. However, as previously stated, the modifications may preferably be made to the structure which supports the BOP. This embodiment of the invention is illustrated in FIGS. 11A and 11B. The rescue vehicle 68 and its structure and function are the same of previously described. Further, the hydraulic system including the control valves 16 remain the same as previously described. The differences in this embodiment as those previously described involve the mounting of the posts, numbered in FIGS. 11A and 11B as 240₁ and 240₂. The BOP support structure includes an upper plate 242, a lower plate 244, and a plurality of support legs 246 extending between the upper and lower plates. A post beam 248 is mounted, such as for example by welding, to respective sets of support legs 246. The posts 240₁ and 240₂ are secured to the post beams 248, or integrally formed therewith and the post beams 248 are set a desired height to properly receive the rescue vehicles, as shown in FIG. 11B. This embodiment avoids having to make modifications directly to the BOP, which may not be acceptable from a quality control point of view if a BOP is not available to a factory controlled welding operation.

Preferably, the BOP rescue system is packaged to be stored on the surface aboard a fire boat, supply vessel, or other easily deployed water craft away from the drilling rig, until the rescue system is needed. If a blowout occurs, and the shear ram fails to shut, the rescue system is needed and it is then lowered from surface into position at the BOP. One method of lowering the rescue system is on coiled tubing, rather than the deployment cable previously described. The coiled tubing may then also provide a conduit for surface generated hydraulic power, with no electric power required at the BOP. This does not preclude the option of installing via cable, and electric cable to generate hydraulic power at the BOP.

The principles, preferred embodiment, and mode of operation of the present invention have been described in the foregoing specification. This invention is not to be construed as limited to the particular forms disclosed, since these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departing from the spirit of the invention.

Claims

1. A blowout preventer and rescue system in combination, comprising:

a. a blowout preventer including a body and at least one pair of rams;

b. a hydraulic system to operate the ram, the hydraulic system including a tail rod accessible from outside the body of the blowout preventer;

c. means associated with the blowout preventer arranged to receive a rescue vehicle; and

d. a rescue vehicle arranged to secure to the receiving means associate with the blowout preventer, the rescue vehicle including means to forcefully contact the tail rod from outside the blowout preventer body, thereby shutting the shear ram.

2. The system of claim 1, wherein the ram is a shear ram.

3. The system of claim 2, wherein the hydraulic system to operate the shear ram including an open line and a shut line, and wherein the system further comprises a control valve in the open and shut lines to controllably disable the hydraulic system.

4. The system of claim 1, wherein the means to receive a rescue vehicle comprises a plurality of horizontally oriented posts arranged on the blowout preventer.

5. The system of claim 1, further comprising a support structure for the blowout preventer, and wherein the means to receive a rescue vehicle comprises a plurality of horizontally oriented posts arranged on the support structure for the blowout preventer.

6. The system of claim 1, wherein the rescue vehicle includes a port securing arm and a starboard securing arm, the arms arranged to secure to the receiving means.

7. The system of claim 4, wherein the rescue vehicle includes a port securing arm and a starboard securing arm, the arms arranged to secure to posts.

8. The system of claim 5, wherein the rescue vehicle includes a port securing arm and a starboard securing arm, the arms arranged to secure to the receiving means.

9. The system of claim 3, further comprising a contactor of the rescue vehicle arranged to contact the control valve in the open and shut lines to controllably disable the hydraulic system.

10. The system of claim 1, further comprising an assist pressure source on the rescue vehicle.

11. The system of claim 1, further comprising a hydraulic coupling on the rescue vehicle to receive hydraulic fluid under pressure from an external source.

12. The system of claim 1, further comprising a deployment cable adapted to couple to the rescue vehicle.

13. The system of claim 1, wherein the means to forcefully contact the tail rod from outside the blowout preventer body includes a hydraulically operated assist rod, and further comprising a locking wedge aboard the rescue vehicle arranged to lock the assist rod when the ram has been operated.