Drill String Safety Valve Reliability: Experimental Measurements of Actuating Torque

Drill string safety valves (DSSVs) are used to prevent blowouts up the drillpipe when unexpected subsurface pressures are encountered in oil and gas drilling. Several case history reviews of well control events have recently shown evidence of poor reliability with DSSVs. Of the problems reported, valve lock-up was most significant, resulting in failure to open or close due to high actuation torque. This paper describes an experimental apparatus and experimental procedures used to quantify the actuating torque of DSSVs under a variety of common operating conditions. Experimentally obtained torque curves are presented for both commercially available and prototype DSSVs, and the results are discussed. Results show the benefit of using special low-torque DSSV designs under certain operating conditions.