Wells – Submerged well – Means removably connected to permanent well structure
Patent
1998-05-06
2000-01-18
Taylor, Dennis L.
Wells
Submerged well
Means removably connected to permanent well structure
166340, 166344, 166368, E21B 712
Patent
active
060150130
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to well intervention systems. In particular, the invention relates to intervention systems for use on sub-sea wells with horizontal sub-sea trees.
DESCRIPTION OF THE RELEVANT PRIOR ART
At the present time, the number of well intervention operations on sub-sea wells is relatively few. However, interventions on platform based wells have contributed to considerable increases in production. Therefore, if the cost of sub-sea interventions is reduced there will be a considerable saving to industry.
An area which has a major cost implication in both capital and running costs is the system for monitoring pressure control during intervention on a sub-sea well. In the drilling mode this equipment, for a horizontal tree, comprises a blow out preventer (BOP) stack, a disconnectable lower marine riser package and a marine riser system. For the well intervention through a conventional sub-sea xmas tree a different pressure control system is used, comprising a safety package to contain the well, a disconnectable riser package (EDP) and a dual workover riser system. Both of these arrangements require complex and expensive handling and running system which occupies a large space on board the vessels which may cause problems with regard to storage of other equipment. If a cost effective and economic alternative to a traditional rigged-based BOP system or industry standard workover riser systems can be derived, then this would offer significant advantages.
Accordingly, several major operators are currently reviewing the feasibility of conducting well intervention operations from lightweight semi-submersible and mono-hull DP vessels for the purposes of well surveillance and management. Cost evaluations of this type of intervention indicate that saving of at least 40-50% are achievable compared with utilising a semi-submersible. If such a vessel could be used it would offer significant advantage in flexibility and speed of manoeuvre to different locations and could also be used for additional uses such as well testing or coil tubing drilling.
Two existing through-BOP stack intervention systems have recently been disclosed; one in applicant's copending U.K. Application No. 9509547.7 for a 5".times.2" dual bore completion tree, and the other in U.K. 9505129.8 for a 5" and 7" monobore system for horizontal/spool trees. These BOP stack intervention systems enable completion/intervention operations to be conducted prior to a conventional tree being deployed or, in the case of a horizontal tree, during the completion and intervention phase. Both systems bring considerable advantages to the operator. Such systems are beginning to be deployed in the industry.
Dual bore skeletal workover risers are used in two roles. Firstly, within the marine riser to run and retrieve the well completion etc. Secondly, to deploy the xmas tree and intervention equipment in open water. In both cases the equipment provides the well control functions required in a well invention role.
In addition, with sub-sea horizontal trees it is important that when the lightweight intervention system is coupled to the horizontal tree there is communication between the tree and the lightweight intervention system for both the main bore and the annulus bore so that control of annulus pressure can be carried out for various well control functions. With most proprietary horizontal trees the annulus line within the wellhead exits beneath the internal tree cap. With such proprietary horizontal trees, in order for the annulus line to be separated from the main bore to provide suitable annulus control, a tubing-annulus bridge must be run and installed in the main bore.
However, as disclosed in International Patent Application No. PCT/GB94/02787 a two-part safety valve system for use with a horizontal sub-sea tree is disclosed. A first valve part containing a ball valve is located within the xmas tree with the valve is normally biased to a closed position. The valve remains in the tree at all times during production and
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Edwards Jeffrey Charles
Morgan Michael Graham
Expro North Sea Limited
Taylor Dennis L.
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