Concurrent Real-Time Distributed Fiber Optic Sensing of Casing Deformation and Cement Integrity Loss

Abstract Subsurface geomechanical changes can cause severe damage to oil and gas well casing strings and cement barriers, which can compromise the zonal isolation of either an abandoned or active well, in the latter case jeopardizing its productive life. A novel system was developed based on laboratory experiments to simultaneously monitor casing deformation and cement integrity using fiber optic distributed temperature and strain sensing (DTSS). The proposed system consists of a hybrid-Brillouin-Rayleigh-based DTSS technique used in combination with two dedicated fiber optic cables. The first is a standard telecommunication fiber, which is used to measure strain changes due to casing deformation. The second cable, coated with a hydrocarbon-sensitive polymer, detects an additional strain caused by the presence of hydrocarbons due to a loss of zonal isolation. The combined system can also detect temperature changes caused by formation fluid invasion from a lower depth into the cement annulus. Since the two cables will be installed side-by-side on the outside of a casing string within the cement sheath, the system can also be used for monitoring the quality of a cementing job. The proposed system provides continuous, real-time and in-situ monitoring of casing deformation and cement integrity to prevent substantial impact on production, or to detect plug failure and hydrocarbon leakage for abandoned and decommissioned wells. It can thereby provide detailed information (i.e. location, type, and event severity) to plan and execute remedial operations, if necessary.