Development of a 3D numerical model for quantifying fluid-driven interface debonding of an injector well

Interface debonding is considered as a major reason for loss of well integrity of a CO2 injector. In this work, a 3D numerical model is developed for simulation of a fluid-driven debonding fracture using the coupled pore pressure cohesive zone method. The equations used in the method are described. The method is validated by numerically reproducing the results of an interface debonding experiment reported in the literature. The 3D model is used to quantify the propagation pressure and the geometry of the debonding fracture in a vertical well. The effects of several key factors in the development of debonding fractures are investigated. The results show that fracture propagation pressure is more sensitive to horizontal stress than to casing pressure. The presence of initial defects at the interface can significantly reduce the propagation pressure and the debonding fracture tends to develop vertically, rather than circumferentially at the interface. The results also demonstrate that the debonding growth is highly influenced by the cement stiffness, critical strength and toughness of the interface, illustrating the importance of appropriate cement design. The method proposed herein presents a useful step towards prediction of loss of well integrity due to interface debonding, and provides improved guidance for cement selection and injection optimization.