This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 23997, ’Case Study: Surface-Controlled Formation-Isolation Valves and Their Application as a Barrier for Temporary Well Suspension,’ by Oguzhan Guven, Joao Mendonca, and Dan Thai, Schlumberger, prepared for the 2013 Offshore Technology Conference, Houston, 6-9 May. The paper has not been peer reviewed. Copyright 2013 Offshore Technology Conference. Reproduced by permission.
To increase deepwater-drilling-rig availability, operators have adopted the strategy of transferring subsea-tree-installation responsibility from offshore drilling rigs to subsea-equipment- support vessels (SESVs). 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 time savings. This paper introduces a fit-for-purpose surface-controlled formation-isolation valve (SFIV) designed for the temporary well suspension required for this strategy.
One of the deepwater subsea-field-development operations being transferred to SESVs is the vertical-tree installation employing the “tree-by-wire” technique. One of the key components of this technique is the use of two remotely operated formation-isolation valves that suspend the well after installation of the tubing hanger. Once the well is suspended, the rig can be moved to the next well. The tree is then installed by use of a heave-compensated wire from an SESV.
A new generation of SFIVs has been designed to enable the well suspension involved in this technique (Fig. 1). Several critical requirements were considered in the development of these valves:
Reliable bidirectional sealing.
Repeatable remote operation.
Fail-as-is: In case of a failure in the control system or the valve itself, the valve must not change its position.
Ability to open under high differential pressure.
High debris tolerance.
Two sizes of SFIVs were developed that meet these requirements. These were fully field tested in 2011 and 2012 in 11 different field installations.
Design and Key Features
The ball section of the SFIV is designed to tolerate the debris common in harsh well environments. The SFIV uses a nontranslating ball valve with bidirectional sealing, which is the ideal valve system for high-debris environments. The ball-valve primary seal is a gastight seal and sustains its integrity even after repeated actuations under pressure differentials.
To allow for increased setting depth, the SFIV actuation section uses a displacement-based fail-as-is mechanism, which functions independently of the setting depth. Most other lubricator valves use a holding system that counteracts the hydrostatic pressure in the event of a control-line leak. At extreme depths, the hydrostatic force acting on the actuation piston creates a large force, increasing the holding force for the valve position as well. This can create operational issues.