Sealing Integrity Evaluation and Optimization of Cement Sheath-Formation Interface under Different Formation Conditions during Fracturing

Fluid channeling caused by seal failure at the cement sheath-formation interface during fracturing is a severe problem in oil gas wells. In this study, a novel model was developed to evaluate interface sealing integrity. The model ' s accuracy was verified based on a self-developed interface seal evaluation device and an experiment. Subsequently, the interface seal under different formation conditions was investigated using this model. The theoretical calculation showed that for a cement sheath-carbonate formation interface, the channeling of acid-fracturing fluid caused interface seal failure and sustained casing pressure in the annulus space between the technical casing and formation. Mutual channeling between the fracturing sections occurred at the cement sheathshale formation interface during fracturing. For a sandstone formation, the interface seal failure caused the channeling between a water-bearing formation and a sandstone formation. Aiming at different formation conditions, the mechanical properties requirements of Young ' s modulus and Poisson ' s ratio of cement sheath were proposed respectively to ensure its seal integrity. The proposed model and method can be used to evaluate and optimize sealing integrity during fracturing.