Simplified Xmas tree using sub-sea test tree

Details Simplified Xmas tree using sub-sea test tree Simplified Xmas tree using sub-sea test tree

1998-07-30

2000-08-29

Lillis, Eileen D.

Wells

Submerged well

Testing

166 861, 166 971, 166368, E21B 712, E21B 2912

Patent

active

061093521

DESCRIPTION:

BRIEF SUMMARY
THE TECHNICAL FIELD

The present invention relates to sub-sea xmas trees.


BACKGROUND OF THE INVENTION

Traditionally, well testing is conducted using a mono-bore conduit to convey production fluids between the marine wellhead, at the mud line, and the xmas tree/flow head at the surface facilities. Various regulatory bodies require the establishment of two barriers between the reservoir and the environment. A mono-bore sub-sea test tree is used to facilitate pressure control. This test tree contains two separate valves to provide the mandatory barriers in the production fluid flow path in order to enable the well to be closed in. The primary annulus barrier is the production packer and the secondary annulus barrier is provided by the contact of blow-out preventer (BOP) pipe rams, seals with the mono-bore riser. Access into the annulus, between the production tubing and the production casing, is required to enable the annulus pressure to be monitored and to be adjusted as necessary. In the traditional systems the annulus flow path is vertical up to the isolation point at which the blow-out preventer (BOP) stack pipe ram seals contact the mono-bore riser. The vertical passage of annulus fluid is blocked at the aforementioned seal and the fluid passage to surface is via a hydraulically actuated valve of the BOP system into external choke or kill lines which are attached to the BOP stack and the marine riser.
U.S. Pat. No. 4,784,225 discloses a well valve assembly for the control of well fluids that flow in the tubing and annulus.


SUMMARY OF THE INVENTION

This structure is not a sub-sea xmas tree and does not operate as a xmas tree.
It is desirable to provide an improved sub-sea xmas tree which avoids the requirement of an expensive xmas tree construction or of the requirement of a BOP stack above the xmas tree to provide annulus barriers.
This is achieved by using a dual bore sub-sea test tree as a simple sub-sea xmas tree whereby the sub-sea test tree provides both a flow path for production fluids and an annulus flow path with the mandatory barriers required.
The dual bore sub-sea test tree contains two ball valves in the production fluid flow path and one or more ball valves in the annulus fluid flow path and thereby fulfils the required regulatory safety standards.
The simplified sub-sea xmas tree comprises three principal components: a wellhead connector, a valve block coupled to the wellhead connector and tree cap coupled to the top of the valve block. The valve block of the sub-sea xmas tree is obtained by securing and sealing the dual bore sub-sea completion test tree inside a cylindrical structural housing. At the lower end the housing is attached to the suitable sub-sea wellhead connector to enable the assembly to be secured to a sub-sea wellhead and is provided with a suitable wellhead profile at the top for attachment of an external tree cap which enables the flow line and control umbilical to be attached to the tree.
ROV (Remotely Operated Vehicle) override units are coupled to each valve mechanism thereby allowing each valve to be actuated between an open and closed position by an ROV.
According to a first aspect of the present invention there is provided a sub-sea xmas tree comprising, cylindrically in shape defining a generally cylindrical interior and a dual bore sub-sea completion tree disposed within said housing, the sub-sea completion tree having a main production bore and an annulus bore substantially parallel to said main production bore, said annulus bore and said main bore extending from one end of the said completion tree to the other end, at least two valve elements disposed in series in said main bore and at least one valve element being disposed in said annulus bore, each of said valve elements being actuatable to move between an open and a closed position to allow fluid communication through said respective bores or to seal said bores, upper connector, said upper connector including communication means for facilitating communication to the annulus and production bores to allo

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Robert H. Rothberg et al., "Research Identifies Designs for Lowering Subsea Production Cost", Oil & Gas Journal, pp. 45-48, No. 10, 91 (1993) Mar.

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