Fibre Reinforced Cement Sheaths for Zonal Isolation in Oil Wells – Quantification and Mitigation of Shrinkage-Induced Cracking

The formation of cracks in the cement sheath and delamination at the cement to steel casing interface due to shrinkage compromises the overall structural stability, imperviousness and durability of oil wells. Particularly, the flow of downhole fluids (e.g. methane or oil) through the cement sheath has become an environmental issue both in offshore and onshore oil wells. This study investigates the impact of fibre reinforcement on the initiation and propagation of cracks in a simulated oil-well section. The study combines a modified setup based on the ASTM-C1581 ring-test with Digital Image Correlation (DIC) in order capture, quantify and measure the initiation and propagation of cracks in the hardening cement and characterize the cracking pattern observed due to autogenous and drying shrinkage deformations and resulting self-induced stresses in the section. The experimental results obtained show the beneficial effect of fibre reinforcement on reducing the extent of cracking by increasing the post-crack ductility of the hardening cement. However, fibre reinforcement had a negligible role in preventing cracking initiation, which is governed by the cement matrix and degree of restraint. This study highlights the benefits of fibre reinforcement as a mitigation measure to reduce shrinkage-induced damage in oil-well cements.