Improving Well Safety With an Innovative Surface-Controlled Subsurface Safety Valve

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 113829, "Improving Well Safety and Maximizing Reserves Using an Innovative Surface- Controlled Subsurface Safety Valve (SC-SSSV)," by Francois Millet, SPE, Harve Petit, and Gery Wallez, Geoservices Equipment, and Philippe LaLanne, Alain Ducasse, and Emile Barzu, Total E&P France, originally prepared for the 2008 SPE Annual Technical Conference and Exhibition, Denver, 21-24 September. The paper has not been peer reviewed. A common cause of failure of surface-controlled subsurface safety valves (SCSSSVs) is a defect in the downhole hydraulic line that controls the valve from the surface. Such a failure generates production losses and requires the intervention of a costly workover rig. To alleviate this type of situation, a system has been developed in which the physical control line has been replaced by a communication system based on electromagnetic (EM) waves. The surface emitter continuously sends a signal to the SCSSSV. Both are designed to be fail-safe. Introduction Lacq field was developed from 1951 to 1957, while solving metallurgical constraints caused by the 15% H2S and 10% CO2 in its gas composition. Nearby, three other fields produce the same long and narrow reservoir and started production in late 1967. From 1968 to 1982, gas production reached approximately 33×106 m3/d, the production from the four fields being centralized at the Lacq treatment plant. These fields are now at the end of their life. The last well was drilled at the end of 1990. Since 1957, well pressures have dropped from 70 MPa to as low as 2 MPa. Unstable water production started in the early 1980s on some wells in the Meillon and Saint Faust fields, causing high operating costs because of water-disposal problems. Furthermore, the normally open velocity and ambient valves used on some wells are no longer acceptable because unstable flowing conditions do not allow accurate and repetitive closure. To extend the life of the wells and maximize the recovery factor, Total E&P France has been looking for a solution to replace subsurface-controlled safety valves (SSCSVs) and nonfunctioning SCSSSVs with new SCSSSVs without the need for a work-over. One solution is surfactant injection at the reservoir level. In this case, the challenge is to free the available nipple and set an injection device in the nipple, again without any work-over or wellhead modification. Avoiding WorkoverThere currently are two types of safety systems being used.The SSCSVs are wireline retrievable (WR) and are calibrated well by well according to the latest production conditions. They are less and less compliant with safety regulations.The SCSSSVs are fail-safe production-rate independent, and testable from the surface whether they are tubing retrievable (TR) or WR.