Patent Grant
7487836
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 running tool 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/running tool is lowered on a segmented length of pipe called a “workover string”. The BOP/running tool is lowered by adding sections of pipe to the workover string until the BOP/running tool 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 tree and release the BOP 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.
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 module 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 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.
A more complete understanding of the present invention may be obtained with reference to the accompanying drawings:
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
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 11 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
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 11 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
Disconnection is achieved by extending the hydraulic cylinder 230. Cylinder extension may be powered through the umbilical 18 or by an 11 ROV using the secondary release hot stab 215 as shown in
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.
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.
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