Quantification of Shrinkage-Induced Cracking in Oilwell Cement Sheaths

Abstract

Summary Ensuring the zonal isolation of hydrocarbon reservoirs is one of the main tasks of the cement sheath, but the development of cracks and debonding between the interfaces might lead to underground water pollution and leaks of oil and gas to the environment. Restrained shrinkage of the cement sheath is one of the most significant causes of cracking, and an experimental investigation has been conducted to quantify how extensive shrinkage-induced cracking might be due to changes in ambient humidity conditions, confinement levels, and mixture compositions. The presence of lateral confinement due to the presence of shale provided an 80% reduction in the cracked area compared to unconfined specimens, but still radial cracks as wide as 200 µm, microannuli up to 100 µm, and cracked areas of 50 mm2 in a representative well section were observed. Additionally, a reduction in crack widths and potential leak paths was obtained by reinforcing the cement slurry with synthetic fibers. A detailed quantification of shrinkage-induced cracking is reported in this study, providing crack information such as position, width, and orientation as a function of time.