A Parametric Study for Radial Cracking in Cement Under Different Loading Events Based on the Stress Intensity Factor

Abstract

AbstractCement is one of the primary barriers in a wellbore and critical to well integrity. Radial cracking is a pervasive failure mode in cement due to the temperature and pressure variation during drilling, completion, or production. This work presents a comprehensive analysis of radial cracking in cement under various loading events. The proposed model estimates the stress intensity factor and fracture surface displacement as indicators for crack propagation and opening, respectively, through a distributed dislocation technique. Three types of radial cracks, divided by their tips terminating at the casing–cement interface, inside cement, or at the cement–formation interface, are considered. Based on this model, we conduct a parametric study for radial cracking under typical loading events such as steam injection, CO2 injection, and high-pressure and high-temperature (HPHT) drilling. Results indicate that the crack near the casing–cement interface has an increased risk for steam injection and HPHT drilling, while all three types of radial cracks are destructive during CO2 injection. The thermal expansion coefficient of cement is a significant parameter for steam and CO2 injection wells. The fluid pressure and the cement’s thickness are crucial to radial cracking under HPHT conditions. Stiffer cement could promote crack opening for steam injection but prohibit the crack deformation for CO2 injection or HPHT wells. Thicker cement would accelerate radial cracking under the three loading events. These findings are helpful in designing cement to maintain long-term integrity.