Coupled thermo-hydro-mechanical analysis of perforated cement sheath integrity during hydraulic fracturing

The wall of perforation hole was directly pressed by the high-pressure fracturing fluid, making cement integrity more challenged in fracturing process. However, the current calculation of perforated cement sheath stress neglects the influence of transient temperature variation during fracturing process. In this work, a fully coupled thermo-hydro-mechanical (THM) model incorporating the transient heat transfer process of fracturing fluid was set up to describe the transient stress variation of cement sheath during fracturing. The maximum tension stress criterion and Mohr-Coulomb criterion were chosen as the criterions for the cement failure. The proposed model was successfully verified through its excellent agreement with experimental observations. In addition, based on the proposed model, the influence of fracturing parameters and cement mechanical parameters on cement integrity was analyzed. The results illustrate that a spindle-shaped tensile-shear failure area is formed near the cement hole. The casing pressure and the cement mechanical parameters are the main controlling factors for the failure of the perforated cement sheath. The extremely low casing pressure are beneficial for maintaining cement sheath integrity. Besides that, only optimizing the Poisson's ratio or elastic modulus of cement cannot maintain the perforated cement integrity unless improving both simultaneously.