Study on debonding issue of cementing interfaces caused by perforation with numerical simulation and experimental measures

The debonding of cementing interfaces caused by perforation will increase the possibility of microannuli/microcrack propagation during hydraulic fracturing. This phenomenon will pose a threat to well integrity not only with stimulation operations but also subsequent long-term production. The objective of this work is to quantitatively investigate the debonding degree of cementing interfaces after perforation. A numerical model was used to simulate the process of the wellbore being penetrated by the perforating gun. Then, a real dimensional perforation experiment was conducted with a circular target specimen. The numerical debonding area of the casing/ cement interface was verified by this experiment with the method of computerized tomography (CT). The numerical-simulation and experiment results show that the cementing-interface debonding is mainly caused by the displacement difference between the casing, cement sheath, and formation during perforation. The debonding area and the microannuli of the casing/ cement interface are larger than those of the cement/formation interface. Sensitivity analysis reveals that the debonding area of the cementing interface shows a positive relationship with the hexogen explosive (RDX) load and the elastic modulus of casing. Therefore, the casing with lower elastic modulus should be preferred to reduce the debonding area of the cementing interface caused by perforation if the principal casing-design criteria were met.