Downhole Safety Valve for Well-Intervention Operations: Design, Testing, and Successful Case History

Abstract

As things progress each year in the oil industry, there is a much greater emphasis on safety. Live well-intervention operations are challenging because of inherent risks and require detailed risk analysis and appropriate mitigation, such as redundant safety devices. This paper presents details of the development, testing, and successful field deployment of a newly designed safety valve that can be used on coiled tubing (CT), jointed tubing (JT), and CT-JT hybrid string applications. This safety valve, located at the junction of the CT and JT, is a key component of the CT-JT hybrid string. Once the CT is connected to the JT, the valve can be pressure actuated to close or open the flow path to the wellbore. This allows the hybrid string to be run in hole (RIH) and pulled out of hole (POOH) with complete wellbore-pressure control. Various methods can be used to activate the valve, such as using surface hand pumps, pressuring between blowout preventers (BOPs), or remotely with pressure differential downhole. Double-flapper check valves have typically been part of a standard well-intervention bottomhole assembly (BHA). However, integrity of these valves is always in question after heavy pumping operations, especially with sand-laden fluids. This new safety valve incorporates a protective sleeve that keeps the flapper assembly covered and in pristine condition in its normally open position, helping to ensure a more reliable seal on closure. Chemical compatibility of elastomers, along with low- and high-pressure sealing reliability, are some of the challenges involved with conventional designs. Considering these limitations, the new safety valve offers a true metal-to-metal, non-elastomeric, spherical-to-spherical, flapper-closure mechanism with low- and high-pressure sealing capability based on ISO 10432/API 14A specifications. The flapper valve is designed and manufactured based on award-winning subsurface safety-valve technology. The safety valve was virtually tested using computational fluid dynamics, followed by functional testing on a full-scale prototype. Validation testing for functional, pressure, and sealing capabilities was conducted at an API type test facility. The safety valve was subsequently deployed and successfully passed field-trial operations.

Coiled Tubing and Jointed Tubing Hybrid-String Well Intervention: Design, Testing, and Case History

“…Some of the benefits of hybrid string include • Extended reach in horizontal wells • Capability to use large CT with higher flow rates • A reduction in horsepower of 30 to 50% for hydraulic fracturing and stimulation (McNeil et al 2011) • Higher cleanout efficiency with the capability of continuous forward and reverse circulation • Smaller and lighter equipment footprint • More weight at the end of string for plug millouts, sidetracks, and long multilaterals • Faster operation compared to JT-only operations • Fracturing through the completion string saves time and money • Hang-off completion string at the end of the job • Fit-for-purpose equipment and tools offers unmatched job safety and efficiency (Ehtesham et al 2011)…”