Abstract

The industry trend of E&P operationsfrom deep water subsea wells is increasing the demand for deepwater drilling rigs. To increase rig availability, operators are resorting to a new strategy of transferring the subsea tree installation responsibility from the offshore drilling rig to a subsea equipment support vessel. The installation from a rig can take 1 to 3 weeks; transferring this responsibility to the support vessel enables the rig to move to the next well sooner and offers significant rig time savings.

This paper introduces a fit-for-purpose surface-controlled formation isolation valve (SFIV) designed for the temporary well suspension that is required as a part of this strategy. The valve was developed, tested, and manufactured in accordance with the ISO-28781 standard. A case study demonstrates the operational time savings achieved by suspending a subsea well with the and landing the tree on heave-compensated wire, call the tree-by-wire technique. Temporary well suspension can be achieved by using plugs or mechanical barrier valves. If plugs are used, the rig must return to remove them after the vertical tree installation, which would partially negate the benefits of the new strategy. Therefore, to fully realize the potential of this new strategy, the SFIV was designed to provide a mechanical barrier that could be remotely opened from the support vessel through application of pressure in the hydraulic control lines without loss of actuation capacity. It's a true fail-as-is valve that eliminates the risk of loss of well control in case of a system failure, which has critical importance in well suspension applications.

Starting in November 2010, several subsea wells around the world were successfully suspended with the SFIV valves. Besides using the SFIV as a suspension valve, operators can use it to perform production build-up tests, downhole lubricator valve for deployment of long production loggin or pereforating guns. This is possible since the valve could be opened multiple times with high differential pressure across the ball valve without any adverse affects on its sealing capacity.

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