Keeping up with safety valve reliability

Ben Lake, of Weatherford, discusses how rigorous testing and validation are essential for ensuring safety valve reliability and performance.

As the last line of defense in protecting life, property, and the environment, subsurface safety valves (SSSVs) are arguably the most critical downhole-completion component. When held to the highest standard of integrity, SSSVs help to assure that wells deliver their full production potential.

Over the years, SSSVs have evolved dramatically in both form and substance to meet the industry’s need for enhanced performance in increasingly challenging fields. Flapper-closure mechanisms have replaced the ball valves of 50 years ago, and have seen further enhancements from flat flappers to streamlined super-curved flappers that enable the same internal diameter, or production area, with a smaller outer diameter. Instead of concentric pistons, modern SSSVs use highly efficient rod pistons with modern non-elastomeric seals designed to last for more than 25 years.

As operators have continued to move into deeper, hotter, and more pressurized reservoirs, safety valve design has kept pace with higher setting-depth, temperature, and pressure capabilities. With ongoing improvements in valve designs, customers have gained the confidence to routinely install tubing-retrieval safety valves (TRSVs) as the primary safety barrier in new wells, with wireline-retrievable safety valves (WRSVs) serving as a contingency in the event of a failure.

While safety valve capabilities have vastly improved, SSSV reliability remains a concern for operators. With a heightened focus on health, safety, and environmental risks—in addition to the challenge posed by low commodity prices—operators need to know that the safety valves installed thousands of feet below the ocean floor will provide a long-term, high-integrity barrier against production losses, expensive interventions, and the need for abandonment.

Reliability is key to performance

SSSV reliability starts with high-level manufacturing and testing/validation standards, a domain governed by the American Petroleum Institute (API) Specification 14A. The 12th edition of API 14A, which becomes effective on 15 January 15 2016, will significantly increase the stringency of SSSV testing.

Applying its decades of experience as an international provider of advanced downhole tools, Weatherford developed a broad platform of modern SSSV solutions. All Weatherford SSSVs are engineered for reliability, with an emphasis on hydraulics, and validated under a robust program that includes more than 3000 rigorous test cycles. The resulting valves are durable and reliable, which helps customers to avoid the production losses and intervention expenses associated with valve failures.

The Weatherford Optimax series includes TRSVs and WRSVs with advanced features that directly address the historic failure points of SSSVs. Rod-piston, flapper-style TRSVs eliminate sleeves, plugs, and other failure-prone mechanisms. The valves are actuated hydraulically via a single control line. The rod-piston assemblies feature non-elastomeric, dynamic seals to mitigate fluid-compatibility and explosive-decompression issues; glide bearings to centralize the piston in the borehole and help maintain sealing under eccentric loads; and metal-to-metal piston-stop seals to provide maximum sealing when the valve is fully open or fully closed. Additionally, Optimax series valves include through-the-flapper self-equalizing systems, which enable technicians to safely match pressures above and below a closed flapper, thereby eliminating the cost of rerouting gas from a nearby well or bringing in pressurization equipment

To date, Weatherford has installed more than 7000 SSSVs worldwide. Of those, nearly 5000 are TRSVs that have provided more than 10,000 years of cumulative service life with zero failures attributable to design or quality issues. No Optimax TRSV has ever failed; however, as a contingency, a Weatherford WRSV can be deployed on slickline to land inside a damaged TRSV. An insert safety valve effectively bypasses the TRSV and helps to restore production at a fraction of the cost of replacement workover. 

New SSSVs meet highest industry standard

This year, Weatherford added three new TRSVs to the Optimax portfolio, all of which meet V1 requirements under the new API 14A standard. They are rated for use in environments with pressures up to 15,000 psi (103 MPa) and temperatures up to 350°F (177°C).

In deepwater reservoirs, where the cost of failure is especially high, operators can use a new SSSV qualified in May and rated for setting at depths up to 6000ft (1829m). A new high-pressure, high-temperature (HPHT) SSSV also meets API V1 standards and was introduced in response to the industry’s push into harsh, HPHT environments. Finally, the new 7in SuperSlim SSSV for large-bore, high-rate gas-well applications was qualified in September and has been installed in a well in Latin America. Several additional installations are planned for early next year in the Asia-Pacific region.

Industry standards are a starting point for operators looking to ensure that equipment will survive the challenging operational conditions encountered during a 25-plus-year well life. Accordingly, all Weatherford TRSVs and WRSVs are slam tested at rates beyond industry standards: at least 100ft/s (30.5m/s) for TRSVs and 150ft/s (45.7m/s) for WRSVs.

To reassure operators that wells could be closed in during blowout conditions, Weatherford performs special high-velocity slam-closure tests. One such test was conducted on a 7in TRSV. The valve was successfully slam tested at 460ft/s (140m/s)—which is equivalent to a production rate of more than 480 MMscf/d (13.59MM cm/d)—making it one of the highest gas-slam-rated valves on the market. 

Increasingly harsh and risky reservoirs, deeper waters, and growing well complexity call for state-of-the-art tools and technologies that deliver high performance and reliability. When it comes to SSSVs, a focus on reliability is paramount. Rigorous testing and validation, along with the implementation of modern designs and features that help address historic failure points, are essential for preventing production losses and protecting crews, equipment, and the environment.

Ben Lake is a global product line manager at Weatherford.