Wells – Submerged well – Wellhead
Reexamination Certificate
1999-03-24
2002-12-24
Shackelford, Heather (Department: 3673)
Wells
Submerged well
Wellhead
C166S366000, C166S341000, C166S358000, C166S339000, C175S007000
Reexamination Certificate
active
06497286
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims the benefit of 35 U.S.C. 119(a) of EP Ser. No. 98302374.8 filed Mar. 27, 1998, and entitled METHOD AND APPARATUS FOR DRILLING A PLURALITY OF OFFSHORE UNDERWATER WELLS.
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for drilling a plurality of wells.
Two conventional methods exist for drilling an offshore underwater well. The first of these is to drill and set a conductor pipe between a surface platform and the sea bed followed by drilling a surface well using a platform wellhead. The Blow Out Preventer (BOP) is located on the surface wellhead. Subsequent casing strings are landed in the surface wellhead. The well is completed by suspending completion tubing from the wellhead and installing a platform tree. A second method is to drill and set a conductor pipe into the seabed using a floating drilling vessel with the wellhead located on the bed. A subsea drilling BOP has to be run on a drilling riser down to the seabed and is connected to the subsea wellhead. A subsea well is drilled with casing hangers landed in the subsea wellhead followed by the tubing completion the well is completed by placing a tree on the seabed wellhead. An alternative subsea option is to use a horizontal tree and then run the tubing.
As the industry moves further offshore and beyond the continental shelf, the water depths being considered are drastically increasing as reservoirs down the flank of the continental shelf and on the ocean floors are discovered. These water depths rule out the use of conventional platforms and their low cost drilling techniques. Floating or tension production platform systems can be used but their drilling footprint into the reservoir is limited, requiring peripheral seabed subsea production support wells. Subsea fields involve considerable complex subsea architecture and require extensive high cost rig intervention.
One way in which an attempt has been made to increase the footprint of a production platform is the provision of a slanted conductor. In such an arrangement, the conductor is supported at an angle by the platform so that it can be run in at an angle thereby increasing the lateral distance between the base of the platform and the location where the conductor meets the seabed. However, such an arrangement is awkward and costly as it requires a specially made structure to support the conductor at an angle. Further, the system will not work in deep water without some support for the conductor at various locations between the surface and the seabed which is not available from a floating platform.
Our co-pending application (Agent's Ref: PAJ07074EP), corresponding to U.S. patent application Ser. No. 09/275,346 filed Mar. 24, 1999 entitled Method and Apparatus for Drilling an Offshore Underwater Well, filed on the same day as the present application discloses a method of drilling an offshore underwater well comprises the steps of installing a riser conduit so that it is substantially vertically supported at a production deck situated substantially at the sea surface and deviates progressively further from the vertical with increasing sea depth, fixing the riser conduit at the seabed in a nonvertical orientation, and drilling the well into the seabed at an angle to the vertical.
As the riser conduit is substantially vertically supported at the production deck, it is possible to use conventional platform drilling and production techniques which help keep the drilling costs to a minimum. Further, because the riser conduit is supported at the surface and at the seabed, and deviates progressively further from the vertical in between, intermediate support is not required but can be provided if necessary by buoyancy modules.
In some fields, the reservoir could be relatively close to the seabed. In such a case, there is insufficient depth for a conventional subsea well which starts vertically at the seabed to be deviated to a sufficient angle to access reservoir formations not already being drained by nearby vertical or deviated wells. Therefore only a limited reservoir acreage can be accessed. With this arrangement some of this deviation from the vertical is already provided before reaching the seabed, so that less deviation is required underground which allows higher angle or horizontal wells to be drilled far along the reservoir. This allows better access to reservoirs which are close to the seabed. However, the most important benefit of this arrangement arises when the water is sufficiently deep that the riser conduit can be deviated to be horizontal at the seabed. Once the riser conduit becomes horizontal, it is possible to extend it some considerable distance along the seabed before drilling into the seabed so that the drilling footprint of a platform can be greatly increased without drilling.
SUMMARY OF THE INVENTION
The present invention relates to an improvement of the method and apparatus of our co-pending application.
Although the system of the co-pending application represents a vast improvement on the prior art in terms of being able to increase the size of the footprint of a platform, it does require the riser conductor to be able to contain the full production pressure and over riser conductor per well.
According to the present invention a method of drilling and completing an underwater well comprises the steps of installing a drilling riser conduit which is vertical at the sea surface to the seabed with the lower end of the drilling riser conduit connected to a template having an inlet port to which the lower end of the drilling riser conduit is connected and a wellhead accessed through the inlet port, such that the drilling riser conduit is at an angle to the vertical at the seabed; fixing the template to the seabed; drilling into the seabed through the wellhead in the template at an angle to the vertical; landing and sealing the well casing and a completion string within the wellhead; and installing a valve tree in the template to direct the flow of production fluid to the surface along a line separate from the drilling riser conduit.
As the wellhead is now at the seabed and the production fluid flows to the surface through a line separate from the drilling riser conduit, it is no longer necessary to have a wellhead at the platform, nor is it necessary for the drilling riser conduit to be lined to take the full reservoir pressure.
There is also preferably provided within the template means for receiving a BOP for installation during well drilling and completing.
A method of landing and locating various components, such as the valve tree and/or the BOP is to lower the components on a skid into the template, and then extend connecting elements together to seal inlet and outlet ports of the components in place.
The well casing is preferably centred in the wellhead by radially projecting centring members.
A further drawback with the system of the co-pending application is that it requires one riser conduit per well. This can be a problem for a large reservoir as each riser conductor requires one well slot on the platform. The hanging loads caused by the casing strings and the heavy mud columns will require high deck support from a large tension leg platform when a large number of wells are being drilled and completed. In addition the drilling range with this concept is limited to the maximum drilling reach from a single point. A large field would now require several platform systems or revert back to using a subsea field system for distant wells.
One major benefit of the present invention arises when several wells can be drilled from a single template. In this case, the template is a junction template provided with a plurality of outlet ports each associated with its own wellhead and valve tree, and a port selector is provided for selectively connecting the inlet port with any one of the outlet ports, the method further comprising drilling into the seabed selectively through more than one outlet port using the port selector selectively to provide acces
Conley & Rose & Tayon P.C.
Cooper Cameron Corporation
Kreck John
Shackelford Heather
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