Mechanical Behavior of Casing–Cement Interface Debonding Failure and Safety Verification Analysis Based on Peridynamics

Frequent occurrences of wellhead sinking highlight the inadequacy of cement's supporting force for the casing, which results in the debonding of the casing–cement interface. The interface debonding leads to the failure of the casing–cement integrity and poses a substantial risk to the overall safety of the wellhead. To ensure wellhead safety, a casing–cement interface model has been established utilizing the peridynamic (PD) method of nonlocal action, aiming to quantify the bonding force at the casing–cement interface. The numerical results align remarkably with load–displacement curves from laboratory tests, validating the effectiveness of the peridynamic method in studying the mechanical behavior of debonding at the casing–cement interface. In addition, further factor analysis was carried out to understand the failure law of the interface. The peak value of interfacial bonding force is found to have a linear correlation with the interfacial coefficient and cement elastic modulus. Specifically, an increase in the interface coefficient from 0.5 to 0.8 and 1 leads to a respective 33% and 53% rise in the peak interfacial bonding force. Similarly, when the elastic modulus of cement escalates from 5 GPa to 10 GPa and 15 GPa, the peak bonding force surges by 93% and 178%, respectively. Field examples show that quantifying cement supporting force on the casing significantly ensures wellhead safety and prevents wellhead sinking.