Summary
There are many examples of wells around the world today that are shut in
because of failure of surface-controlled subsurface safety valves (SCSSVs).
While these valves are generally very reliable, the control line that runs to
the surface in the annulus is susceptible to plugging by contaminants in the
hydraulic control fluid and also to corrosion, which causes leaks; both are
outcomes that render the valve inoperable. The failure of the control line also
means that the contingency solution of installing a wireline-retrievable
surface-controlled subsurface safety valve (WR-SCSSV) is not possible.
When a safety valve fails, the most common remedial solution today involves
installing a subsurface-controlled safety valve (SSCSV), such as an ambient
valve or storm choke. While this solution is lower cost and more
straightforward than performing a full rig-based well workover, it is not as
safe. SSCSVs are directly influenced by changing well-flow conditions, such as
high flow rates and low pressures, or by water slugs, and thus are notoriously
unpredictable in operation. Additionally, they are not controllable from
surface and not fail-safe, which is undesirable from a well-control and safety
standpoint.
By transmitting electromagnetic (EM) signals from surface to downhole, it is
possible to control downhole hardware. A wirelessly controlled safety valve has
been developed that can be retrofitted into a well using conventional slickline
intervention equipment and procedures. Being controllable from surface and of a
fail-safe closed design, this valve offers both functional and safety
advantages over existing SSCSV solutions. This new valve also offers a
retrofittable solution for wells having no hydraulic control line installed. In
situations where a capillary string may need to be installed for foam- or
chemical-injection purposes, it also provides an opportunity to free up the
hydraulic control line.
A prototype valve was subjected to qualification and functionality testing
in accordance with a modified International Organization for Standardization
(ISO) 10432 test procedure. This testing was followed by installation in an
onshore gas well for a 6-month trial that involved both flowing and injection
phases. The valve was cycled and inflow-tested regularly and performed
reliably, consistently, and fully in accordance with specification throughout
the trial period.
This successful trial of a new wirelessly controlled safety valve marks the
introduction of a more-controllable and -predictable alternative to an ambient
valve or storm choke, minimizes deferred production, and increases the well's
safety. Following the successful onshore trial, the valve is now considered
ready for wide-scale field application onshore, and at the time of writing this
paper, plans for performing a first trial on an offshore platform are well
advanced.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
19 January 2010
- Meeting paper published:
23 March 2010
- Revised manuscript received:
30 June 2010
- Manuscript approved:
3 September 2010
- Published online:
13 January 2011
- Version of record:
22 February 2011
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