Riserless modular subsea well intervention, method and apparatus

Abstract

A subsea well intervention system that permits dynamic disconnection from subsea well intervention equipment without removing any of the equipment during a drive-off condition is provided. The system includes a blowout preventer module operatively connected to a subsea tree and a subsea control system. The subsea control system is connected via electrical jumper to an ROV's tether management system. The subsea control system is connected via hydraulic jumpers to a multipurpose fluid-injection skid and one or more hydraulic accumulation banks. A fail-safe disconnect assembly is utilized with respect to the electrical jumper in order to provide easy removal during a drive-off condition.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to a subsea well intervention system, and more specifically to a riserless modular subsea well intervention system.

Oil and gas wells frequently require subsurface maintenance and remediation to maintain adequate flow or production. This activity is commonly referred to as “workover.” During the workover specialized tools are lowered into the well by means of a wire line and winch. This wire line winch is typically positioned on the surface and the workover tool is lowered into the well through a lubricator and blowout preventer (BOP). Workover operations on subsea wells require specialized intervention equipment to pass through the water column and to gain access to the well. The system of valves on the wellhead is commonly referred to as the “tree” and the intervention equipment is attached to the tree with a BOP.

The commonly used method for accessing a subsea well first requires installation of a BOP with a pre-attached tree running tool (TRT) for guiding the BOP to correctly align and interface with the tree. The BOP/running tool is lowered from a derrick that is mounted on a surface vessel such as a drill ship or semi-submersible platform. The BOP/TRT is lowered on a segmented length of pipe called a “workover string”. The BOP/TRT is lowered by adding sections of pipe to the workover string until the BOP/TRT is sufficiently deep to allow landing on the tree. After the BOP is attached to the tree, the workover tool is lowered into the well through a lubricator mounted on the top of the workover string. The lubricator provides a sealing system at the entrance of the wire line that maintains the pressure and fluids inside the well and the workover string. The main disadvantage of this method is the large, specialized vessel that is required to deploy the workover string and the workover string needed to deploy the BOP.

Another common method for well intervention involves the use of a remotely operated vehicle (ROV) and a subsea lubricator to eliminate the need for the workover string and therefore the need for a large, specialized vessel. Current state of the art methods require that the BOP and lubricator are assembled on the surface and then lowered to the seafloor with winches. When the BOP is in the vicinity of the tree, the ROV is used to guide the BOP/lubricator package into position and lock it to the tree. A control umbilical, attached to the BOP/lubricator package is then used to operate the various functions required to access the well. The workover tool can then be lowered on a wire line winch and the ROV is utilized to install the tool in the lubricator so that workover operations can be accomplished. The umbilical provides control functions for the BOP as well as a conduit for fluids circulated in the lubricator.

A common problem with both the workover string method and the BOP/lubricator package method is encountered during a “drive-off” condition. A drive-off condition occurs when by accident or design the surface vessel is forced to move away from its position over the well without first recovering the equipment attached to the tree. Vessels in deep water are commonly held in position over the well by computer controlled, dynamic thrusters. If for any reason, there is a failure in the computer, the thrusters, or any related equipment, the vessel will not be able to hold position or it may be driven off position by incorrect action of the thrusters. In the event of a drive-off condition, the operator must close the valves on the BOP and release the disconnect package so that the intervention equipment can be pulled free of the well. With the drill string method, the BOP is supported by the drill string. With the BOP/Lubricator method, the equipment must be lifted by the surface winches that must be kept continuously attached to the BOP/lubricator equipment. In either case, large pieces of equipment remain hanging below the vessel until they can be recovered.

What is needed is a method and apparatus for the installation of subsea well intervention equipment that eliminates the need to recover the equipment in a drive-off condition.

SUMMARY OF THE INVENTION

A riserless subsea well intervention system that permits dynamic disconnection from subsea well intervention equipment without removing any of the equipment during a drive-off condition is provided. The system includes a blowout preventer module operatively connected to a subsea tree, a lubricator assembly including a disconnect module functionally attached to the blowout preventer module, and an umbilical module including a fail-safe disconnect assembly. A running tool module is utilized to functionally guide the blowout preventer module into alignment with the subsea tree. The lubricator assembly is functionally effective to provide access to the interior of the blowout preventer and the subsea tree by well intervention equipment. The umbilical module is functionally connected to a control mechanism, and includes one or more release systems for disconnecting at least the blowout preventer module from the remaining components of the well intervention system. The fail-safe disconnect assembly is disconnected preferably using hydraulic power provided by the umbilical or alternatively by a remotely operated vehicle.

Also disclosed is a method for constructing a riserless subsea well intervention system. The method includes connecting a blowout preventer module to a subsea tree, connecting a lubricator module to the blowout preventer module, and connecting an umbilical to the lubricator module using a fail-safe disconnect. Each of these steps is preferably carried out by a remotely operated vehicle. In this manner, the fail-safe disconnect can be disconnected during a drive-off condition so that the blowout preventer module and the lubricator module, as well as other well intervention equipment, remain connected to the subsea tree.

Also disclosed is a system and method for constructing a riserless subsea well intervention system without an umbilical module. The method includes connecting a blowout preventer module to a subsea tree, connecting a subsea control system to the blowout preventer, connecting an electrical flying lead from the subsea control system to an ROV's tether management system using a fail-safe disconnect assembly, and connecting a multi-purpose fluid injection skid and one or more accumulation banks to the subsea control system for controlling the subsea well intervention operations.

Also disclosed is a preferred embodiment of the fail-safe disconnect assembly, which includes a male disconnect coupling having a coupling actuator. The male disconnect coupling is connected to the coupling receptacle of a female disconnect coupling. The female disconnect coupling is preferably located on the lubricator module. The fail-safe disconnect assembly is disconnected using hydraulic power provided by the umbilical or by a remotely operated vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be obtained with reference to the accompanying drawings:

FIG. 1 shows an illustrative embodiment of a riserless modular subsea well intervention system of the present invention.

FIG. 2 shows a preferred embodiment of the disconnect assembly of the present invention.

FIGS. 3A and 3B illustrates the male disconnect coupling of the disconnect assembly of FIG. 2.

FIGS. 4A and 4B illustrates the female disconnect coupling of the disconnect assembly of FIG. 2.

FIGS. 5A and 5B illustrates the hydraulically powered connection made by the disconnect assembly of FIG. 2.

FIG. 6 illustrates the initial setup for a second illustrative embodiment of a riserless modular subsea well intervention system of the present invention.

FIG. 7 illustrates the connection of the blowout preventer and subsea control system for the second illustrative embodiment of the riserless modular subsea well intervention system.

FIG. 8 illustrates the connection of the subsea control unit and electrical flying lead for the second illustrative embodiment of the riserless modular subsea well intervention system.

FIG. 9 illustrates the final configuration for the second illustrative embodiment of the riserless modular subsea well intervention system.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The method and apparatus described herein allows modular installation of a riserless subsea well intervention equipment and eliminates the need to recover the equipment in a drive-off condition. Dynamic disconnection from the tree-mounted equipment is accomplished by a special, fail-safe disconnect assembly, half of which is fitted to the subsea end of the umbilical and the other half being mounted to the lower end of the lubricator assembly. The system described herein has the further advantage of operation with a smaller vessel than prior art systems because of the smaller and less specialized surface handling equipment used by the present invention (hydraulic reservoir skid, hydraulic accumulator, hydraulic power unit, and hydraulic umbilical reel). Furthermore, leaving the subsea equipment secured to the tree during a drive-off condition reduces the disconnect time and provides less risk of damage to the tree or the environment.

Referring to FIG. 1, a preferred embodiment of the present invention is illustrated. The subsea well intervention system 10 consists of a lubricator assembly 12, a subsea blowout preventer module 14, a running tool module 16, and an umbilical 18, such as a 7-line umbilical, with fail-safe disconnect assembly 20. One of skill in the art will appreciate that an umbilical control system is required to implement the present invention and includes, without limitation, an umbilical reel assembly 19, umbilical sheaves 21, a hydraulic reservoir skid (not shown), a hydraulic accumulator (not shown), and a hydraulic power unit with an interruptible power supply (not shown). Blowout preventer module (BOP) 14 is operatively connectable to a subsea tree 22 using pre-attached running tool module 16, which is functionally effective to guide BOP 14 into alignment with the subsea tree 22. Running tool module 16 is selected to specifically fit the target subsea tree and is commonly manufactured either by or for the tree's manufacturer for such a purpose.

Lubricator assembly 12 is operatively connectable to BOP 14 and is functionally effective to provide access to the interior of BOP 14 and subsea tree 22 by well intervention equipment (not shown). Lubricator assembly 12 includes a tapered stress joint 24 for control of bending loads applied to BOP 14 and a grease head 26 for insertion of the workover tool (not shown). Lubricator assembly 12 also includes necessary valves and flow passages that all the seals between all components can be tested before the tree valves are opened.

Umbilical 18 is functionally connected to a control mechanism (not shown). Umbilical 18 contains one or more release systems for disconnecting at least BOP 14 from the remaining components of the subsea well intervention system. A preferred embodiment of such a release system is fail-safe disconnect assembly 20. Disconnect assembly 20 is used to connect the umbilical 18 to subsea well intervention equipment, and specifically to lubricator assembly 12. The disconnect assembly 20 is “fail-safe” in that it is hydraulically powered to connect and it remains connected until hydraulically powered to release. Normal operation of disconnect assembly 20 is controlled through the umbilical 18. A secondary release system, operated by an ROV is also provided. The multiple hose passages of the umbilical 18 are sealed by mechanical valves that are opened as the disconnect assembly 20 is powered to the connect condition and automatically closed as the disconnect assembly 20 is powered to release.

Referring to FIGS. 2-5, a preferred embodiment of the fail-safe disconnect assembly 20 is illustrated. FIG. 2 shows the disconnect assembly 20 with male disconnect coupling 202 and female disconnect coupling 204 connected.

FIGS. 3A and 3B show the male disconnect coupling 202 having a guide cone 208, an ROV handle 210, an alignment guide slot 212, an index pin 214, a female hose connector 216, and a coupling actuator 206. The male disconnect coupling also features a secondary release ROV hot stab 215 with a protective plug 217. FIGS. 4A and 4B show the female disconnect coupling 204 having a support housing 218, a mounting flange 220, an alignment guide 222, an index pin receptacle 224, a male hose connector 226, and a coupling receptacle 228.

In a preferred aspect of the present invention, female disconnect coupling 204 is mounted prior to subsea installation on lubricator assembly 12 using mounting flange 220. An ROV is then used to connect the male disconnect coupling 202 (attached to the umbilical 18) to the female disconnect coupling 204. The ROV's manipulator is used to “grab” the ROV handle 210 and guide the two coupling halves together using guide cone 210. Alignment guide 222 and alignment guide slot 212, as well as index pin 214 and index pin receptacle 224, are then utilized to properly position male coupling actuator 206 with female couple receptacle 228.

As shown in FIGS. 5A and 5B, the hydraulically powered connection and disconnection of the fail-safe disconnect assembly 20 is accomplished with a single hydraulic cylinder 230. The force required to engage the umbilical hose connectors 216, 226 is provided by the hydraulic cylinder 230 pulling the coupling actuator 206 into the coupling receptacle 228. Once the male coupling actuator 206 is landed on the female coupling receptacle 228, initial retraction of the hydraulic cylinder 230 in the actuator 206 operates a ball grab 232 that locks into a recess 234 in the female receptacle 228. As the hydraulic cylinder 230 continues to retract, the hose connectors 216, 226 are pulled 11 together and forced to engage. Engagement of the hose connectors 216, 226 causes the check valves 236 in both the male and female hose connectors 216, 226 to open. Continued retraction of the hydraulic cylinder 230 allows mechanical latches 238 in the actuator 206 to engage a recess 240 in the receptacle 228. After the latches 238 are engaged, the coupling halves are locked together and no further action of the hydraulic cylinder 230 is required.

Disconnection is achieved by extending the hydraulic cylinder 230. Cylinder extension may be powered through the umbilical 18 or by an ROV using the secondary release hot stab 215 as shown in FIG. 3A. As the cylinder 230 extends, a cam on the cylinder rod retracts the mechanical latches 238 in the actuator 206 and the coupling halves are biased apart due to the force of grab spring 242. Continued extension of the hydraulic cylinder 230 allows the ball grab 232 to retract and the male coupling half is thereby disconnected.

Another embodiment of the present invention is a method for constructing a riserless subsea well intervention system including the steps of first connecting a blowout preventer module having a pre-attached running tool to a subsea tree, then connecting a lubricator assembly to the blowout preventer module, and finally connecting an umbilical to the disconnect module using a fail-safe disconnect. Each of these connections is preferably carried out by an ROV. In this manner the fail-safe disconnect can be disconnected during a drive-off condition, thereby the blowout preventer module including the running tool and the lubricator assembly remain connected to the subsea tree during the drive-off condition. The fail-safe disconnect preferably contains a male coupling half located on the umbilical and a female coupling half located on the lubricator assembly. The fail-safe disconnect is preferably disconnected using hydraulic power provided by the umbilical, or alternatively using hydraulic power provided by an ROV.

Another preferred embodiment of the present invention is illustrated in FIGS. 6-9, in which the riserless subsea well intervention system further includes a subsea control unit that eliminates the need for an umbilical module. As shown in FIG. 6, two ROVs 100 A/B are deployed from a floating vessel 104, each ROV 100 A/B having a dedicated Tether Management System (TMS) 102 A/B.

Referring to FIG. 7, wire line 110 is used to position a blowout preventer module and a subsea control unit 108. As described above, the blowout preventer module is operatively connectable to subsea tree 106 using a pre-attached running tool module, which is functionally effective to guide the blowout preventer module into alignment with the subsea tree 106. The running tool module is selected to specifically fit the target subsea tree and is commonly manufactured either by or for the tree's manufacturer for such a purpose. The subsea control unit 108 connects to the BOP by a hydraulic connector

Subsea control system 108 is preferably a multiplexed, electro-hydraulic control system. Thus, a topside control unit located on vessel 104 can communicate via a data link with subsea control system 108 for control of hydraulic function and monitoring of data. As shown in FIG. 8, ROV 100A is used to connect an electrical flying lead 112 from the subsea control system 108 to TMS 102A to create an electrical jumper. Thus the ROV's umbilical cable 114 is used to provide a communications link between subsea control system 108 and the topside control unit via the electrical jumper. A redundant subsea control system and the deployment of two ROVs give the control system redundancy. In this embodiment, topside controls would be split with dual redundant consoles and separate uninterrupted power supply for emergency backup power.

Referring to FIG. 9, a multi-purpose fluid injection skid 118 and one or more hydraulic accumulators 120 are lowered to the sea floor using a winch from vessel 104, with placement assistance from one or more ROVs. ROV 100B is used, for example, to connect a hydraulic flying lead 116 from the subsea control system 108 to a multi-fluid hydraulic injection skid to create a hydraulic jumper. The hydraulic accumulator banks 120 are used to supply hydraulic power to the subsea control system 108 and is connected by ROV 100A, for example, by use of a hydraulic jumper 122. The multi-purpose fluid injection skid 118 provides hydraulic fluid, grease injection, and sea water for the subsea control system. The hydraulic fluid portion of the skid includes storage for oceanic hydraulic fluid (typically water or glycol based) and pumping means for pumping the hydraulic fluid through hydraulic jumpers 116 and 122 to make-up hydraulic power for a spent accumulator bank 120. The grease injection portion of the skid includes storage for grease and the pumping means necessary to pump the grease to the subsea control unit 108 via hydraulic jumper 116. The grease is ultimately pumped into the grease head and used to make a seal around the wire line entering the top of the lubricator. The sea water portion of the skid includes pumping means necessary to pump surrounding seawater to the subsea control unit 108 via hydraulic jumper 116. Sea water is ultimately used to flush out the lubricator before disconnecting it so as to not release any contaminates into the water.

The combined system described in FIG. 9 is then used to operate the various functions described above to access the subsea well. The system described In FIGS. 6-9 allows modular installation of the subsea equipment and eliminates the need to recover certain equipment in a drive-off condition. Disconnection from the tree-mounted equipment is accomplished by a special, fail safe disconnection device (such as the device described herein with respect to FIGS. 2-5) fitted to the end of the applicable jumpers, such as electrical flying lead 112. For example, during a drive-off condition, the blowout preventer, subsea control system 108, multi-purpose fluid injection skid 118, and hydraulic accumulators 120 remain with the tree 106 while the ROVS 100 A/B, TMS's 102 A/B, wire line 110, and the electrical jumper 112 are taken away with vessel 104. As mentioned before, leaving the subsea equipment secured to the tree during a driveoff condition reduces the disconnect time and provides less risk of damage to the tree or the environment.

It will be apparent to one of skill in the art that described herein is a novel method and apparatus for installing and disconnecting a riserless modular subsea well intervention system. While the invention has been described with references to specific preferred and exemplary embodiments, it is not limited to these embodiments. For example, although the invention herein is described in reference to a specific preferred fail-safe disconnect assembly, it should be understood that the teaching of the present invention are equally applicable to other alternative disconnect assemblies. The invention may be modified or varied in many ways and such modifications and variations as would be obvious to one of skill in the art are within the scope and spirit of the invention and are included within the scope of the following claims.

Claims

1. A method for constructing a riserless subsea well intervention system, comprising: establishing an electrical communication link between a surface control console and a subsea control system module by a remotely operated vehicle's tether management system; andestablishing a fluid connection between the subsea control system module and a subsea source for hydraulic power; andestablishing a second fluid connection between the subsea control system module and a hydraulic accumulator.

2. The method of claim 1, further comprising providing a fluid connection between the subsea control system module and a multi-purpose fluid injection skid.

3. The method of claim 1, wherein the source for hydraulic power is a multi-purpose fluid injection skid.

4. The method of claim 2, wherein the fluid connection between the subsea control system module and the multi-purpose fluid injection skid remains connected when the surface control console is disconnected from the subsea well intervention system.

5. The method of claim 3, wherein a fluid is pumped between the multi-purpose fluid injection skid and the'hydraulic accumulator.

6. The method of claim 3, wherein the multi-purpose fluid injection skid and the hydraulic accumulator rest on the sea floor.

7. The method of claim 3, wherein the multi-purpose fluid injection skid is self-powered.

8. The method of claim 7, wherein the multi-purpose fluid injection skid is rechargeable by the remotely operated vehicle.

9. A riserless subsea well intervention system, comprising: a subsea control system;an electrical communication link between a surface control console and the subsea control system, wherein the electrical communication link is connected by a remotely operated vehicle's tether management system; anda fluid connection between the subsea control system and a subsea source for hydraulic power, anda second fluid connection between the subsea control system and a hydraulic accumulator.

10. The system of claim 9, further comprising a fluid connection between the subsea control system and a multi-purpose fluid injection skid.

11. The system of claim 10, further comprising a fluid connection between the multi-purpose fluid injection skid and the hydraulic accumulator.

12. The system of claim 10, wherein the multi-purpose fluid injection skid and the hydraulic accumulator rest on the sea floor.

13. The system of claim 10, wherein the multi-purpose fluid injection skid is self-powered.

14. The system of claim 13, wherein the multi-purpose fluid injection skid is rechargeable.

15. The method of claim 2, wherein the multi-purpose fluid injection skid is powered by the remotely operated vehicle.

16. The system of claim 10, wherein the multi-purpose fluid injection skid is powered by the remotely operated vehicle.