Application of Slip Interface Theory in the Evaluation of Casing Well Cementing Quality

The classical elastic wave theory can model the propagation of the acoustic field in a cased well as a structure with cylindrical layers. A thin fluid annulus between the interface is often used to simulate uncemented conditions. However, the traditional cased borehole models and their associated techniques are idealized approximations. In reality, irregular and rough interfaces, along with poor cement bonding, lead to partial contact between the interfacial surfaces. This results in shear coupling as acoustic waves propagate through the interface. Therefore, the fluid annulus model is not applicable to the partially cemented interface. To address this limitation, we propose a casing coupling model based on slip interface theory, which describes the gradual transition of the interface from well cemented bonding to complete debonding. Simulation results show that combining the casing coupling model with the classical model allows for modeling the amplitude changes in the acoustic-wave measurement from well bonded to free casing conditions. Based on the theoretical modeling, we introduce a method to quantitatively evaluate cementing quality at the casing-cement interface using first-arrival wave data. To validate the effectiveness of slip interface theory for assessing cementing quality, we conducted verification tests on two experimental wells with varying uncemented sector angles (USA) and cement densities. The results reveal that the shear coupling stiffness curve is sensitive to small USA but relatively unaffected by changes in cement density. Finally, we applied slip interface theory to interpret field acoustic data. Compared to conventional methods, the shear coupling stiffness curve from the slip interface model is more effective in identifying small USA or channeling issues.