Workovers in Sour Environments: How Do We Avoid Coiled Tubing (CT) Failures?

Abstract

Workover of wells contaminated with hydrogen sulfide (H 2 S) is a difficult task. Coiled tubing (CT) has become one of the mainstays in treating this type of well, but failures do occur, such as tubing recovered with leaks or catastrophic parting, which can leave several thousand feet of tubing, including bottomhole assemblies (BHAs), to be fished.Corrosion control is essential to protect production equipment, and to avoid CT failures during acid treatments. Also essential for the safe use of CT are the proper selection of metallurgy for the downhole environment, appropriate use of H 2 S inhibitors, nondestructive testing of the coil before usage, and periodic sampling of the coil for physical examination. Other precautionary measures are still in the development stages.In this paper, we discuss two case histories of CT failure during workover in sour environments. The analyses performed to determine causes and recommended practices to avoid the reoccurrence of these failures are included along with a set of guidelines for the safe use of CT in sour-well workovers.