Numerical investigation of debonding extent development of cementing interfaces during hydraulic fracturing through perforation cluster

Abstract The perforation will damage the sealing integrity of cement sheath/cementing interfaces around the hole more or less, especially the debonding of cementing interfaces may lead to the fluid channeling during hydraulic fracturing. In this work, a laboratory experiment were used to verify the cohesive zone method (CZM) for simulating the debonding extent of casing/cement interface from a single hole during hydraulic fracturing. Then the debonding degree of cementing interfaces through perforation cluster during fracturing was investigated by using CZM. The numerical analysis results showed that the axial debonding length of the cement/formation interface is longer than which of casing/cement interface under the same working conditions. When the debonding zone around the perforation holes connected to each other, the cement/formation interface debonded faster than that of the casing/cement interface under the pressure of fracturing. The parameter sensitivity analysis shows that it is beneficial to diminish the debonding extent of cementing interfaces by reducing the viscosity of fracturing fluid and the pump pressure. The reliability of CZM method was validated by means of the peak values of critical failure pressure and casing displacement during lab scale fracturing experiment. Improving interfacial bonding strength and reducing the elastic modulus of the cement sheath can effectively promote wellbore integrity during hydraulic fracturing. This work can be used to evaluate the sealing performance of the cement sheath under the hydraulic fracturing and to provide guidance for fracturing planning.