Monobore riser bore selector

Details Monobore riser bore selector Monobore riser bore selector

1998-10-13

2001-01-09

Neuder, William (Department: 3672)

Wells

Submerged well

Connection or disconnection of submerged members remotely...

C166S341000, C166S348000, C166S359000

Reexamination Certificate

active

06170578

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a system for coupling a monobore high pressure riser, a dual bore sub-sea tubing hanger and a dual bore tubing hanger running tool together. In particular, the invention relates to a monobore riser cross-over apparatus for providing communication between the monobore riser and the dual bores.
DESCRIPTION OF THE RELEVANT PRIOR ART
A conventional sub-sea well system incorporates a dual bore tubing hanger set within a sub-sea wellhead system, with a dual bore sub-sea xmas tree installed onto the wellhead thereby establishing discrete flowpaths for the production, and annulus access bores and communication to downhole safety equipment, the downhole safety valve (DHSV), electrical equipment for measuring pressure and temperature, and other well operating functions in the case of multi-lateral completions.
During the installation procedure wireline plugs are installed through the tubing hanger running tool into the tubing hanger to accommodate the requirements of the statutory authorities, to maintain well control during the interval between the disconnection of the blow-out preventer (BOP) stack from the wellhead and the installation of the xmas tree. Within the production bore a preliminary barrier is established by the installation of a deep-set plug in the downhole completion which is located at or below the packer assembly. A secondary barrier is established by the installation of a second similar plug within a suitable profile in the tubing hanger production bore. On the annulus side, the primary barrier is the downhole packer assembly, and a secondary barrier is established by the installation of a similar wireline set plug in a suitable profile in the annulus access bore within the tubing hanger. Thus, the statutory requirement to provide two barriers between the reservoir and the environment is satisfied.
Once the dual bore xmas tree has been installed onto the wellhead, the wireline plugs are retrieved to facilitate production of the reservoir through the sub-sea xmas tree.
In order to access the two discrete bores of a conventional dual bore production system for the installation of wireline plugs, historical practice has been to utilise a dual bore riser system as shown in
FIG. 1
of the drawings. It should be understood that the capital cost of such a conventional dual bore riser system is significant. The most common and economic form of a dual bore riser is the skeletal riser in which two separate tubular members are clamped together at regular intervals to form discrete joints which are usually about 50 ft. in length and which are connected together to form the dual bore riser string. The operational depth limit of such a riser is generally agreed to be about 3000 ft. An alternative to the conventional dual bore skeletal riser system is sought in order to reduce cost, to extend the ability to make available risers in a variety of sizes available a short delivery notice and to extend the opportunities of using sub-sea production systems to exploit oil reservoirs in water depths exceeding 3000 ft. One of these alternatives is already described in applicant's copending International Patent Application PCT/GB96/00435 for a Dual Bore Riser using casing and coiled tubing.
A monobore riser system can be made for less cost and can be made to work in greater water depth much more economically than a dual bore riser system. However, a single bore riser has a significant limitation in that it cannot, on its own, access a dual bore system without there being some means provided to permit an exclusive selection of which of the two bores within the sub-sea tubing hanger to access.
Traditionally, the means by which such an exclusive selection has been accomplished has been to arrange the production bore (A) to be straight and vertical; with the annulus access bore (B) being “kicked off” to one side in the form of an inverted “Y” shape as shown in
FIG. 2
of the drawings. Access into the production bore (A) is simply straight down the vertical path and, because the production bore is always larger than the annulus access bore, components which run into the production bore are too large to fit into the annulus bore. Access into the annulus bore is accomplished by blocking the path into the production bore by the installation of a plug, called a whipstock (C), using wireline techniques an example of which is also shown in
FIG. 2
of the drawings. The whipstock (C) has a top profile (D) which shaped to encourage components into the annulus access bore (B) to change direction laterally to enter the “Y” branch into the annulus access bore.
One problem of this existing arrangement is that the whipstock has to be run-in on wireline to block the production bore and access the annulus bore. This requires time both to run the tool in and to withdraw the tool which is relatively expensive. In addition, each time there is a wireline operation run, there is a risk of complications.
One proposed solution to overcoming the problems associated with the wireline run whipstock is disclosed in published U.K. Patent Application GB 2258675A to B.P. Exploration Operating Company Limited. This specification discloses a workover system for sub-sea oil and/or gas wells which has a converter to allow the system to be used to access any of the bores of a parallel multiple bore well. A movable bored inner portion can be rotated or swung in pendulum fashion to connect a single bore to one of two parallel bores. In the rotatable embodiment, rotation may be effected using a rack and pinion arrangement and in the pendulum embodiment this may be achieved using hydraulically operated rams or pistons. In both embodiments actuation may be achieved by using electric motors or mechanically by an ROV and they may be controlled from a surface rig or vessel using the hydraulic control system of the workover BOP. However, this prior art reference is intended to couple a single bore to any one of a number of parallel bores in an oil or gas well and in particular one of a number of parallel wells. There is no specific disclosure of the mechanism being used to couple between a single bore and a production or annulus bore and to allow access between the single bore and the production bore and/or the annulus bore.
An object of the present invention is to provide an improved mechanism for facilitating access from a monobore riser to a production bore or annulus bore.
A further object of the present invention is to provide improved access to a production bore or annulus bore in a dual bore system from a monobore riser without using a whip stock run in on a wireline.
SUMMARY OF THE INVENTION
A further object of the present invention is to facilitate communication between a monobore riser and dual bores within a dual bore sub-sea tubing hanger which can be readily controlled from the surface.
This is achieved by providing a bore selector apparatus disposed within the bore of a BOP stack and which can be coupled between casing or tubing and a sub-sea test tree. The bore selector apparatus can be actuated from the surface or from an ROV to provide a coupling exclusively between the tubing bore and the production bore or between the tubing bore and the smaller annulus bore.
In a preferred embodiment this is achieved by using a rotatable ball valve element located in a housing disposed between the casing/tubing and a sub-sea test tree, the ball valve element being apertured and being rotatable between a first position whereby the aperture connects the production tubing to the production tubing bore and in a second position is rotated whereby the aperture connects the annulus bore to the tubing or casing bore. When one of the production or annulus bores is connected to the tubing bore, then the other bore is isolated or disconnected.
In yet another embodiment of the invention the bore selector mechanism is implemented by a flapper plate mechanism which is moveable by a cylindrical sleeve between a first open position whereby access to the production is blocked and there is

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