Evaluation of Cement Mechanical Performance in Thermal Storage Wells

Cement endurance is crucial for high-temperature reservoir thermal energy storage applications. Cyclic pressure and temperature fluctuations during injection and production processes can lead to the degradation of cement strength and induce plastic deformation. In this study, we assess the mechanical properties of cement with the formulation of 60% Class G cement and 40% silica flour. These cements were cured at 50 °C but subjected to temperature cycling between 50 °C and 200 °C. We collected data on the mechanical strength, Young's modulus, Poisson's ratio, and plasticity of the cement by measuring its stress-strain curves under high-pressure and high-temperature conditions, specifically up to 20 MPa and 180 °C. The findings revealed that the cement exhibits higher plasticity under high pressure and high temperature conditions. After two months thermal cycling in the oven under dry conditions, the cement experienced strength degradation, manifesting as a reduced yield strength and lower Young's modulus. The thermal cycling also led the cement to behave more elastically than plastically. By employing a thermoporoelastic model and performing an operational safety analysis, it became evident that a reduced Young's modulus resulted in safer well conditions, with a reduced likelihood of shear failure, tensile cracks, and debonding. Although thermal cycling was initially suspected to induce plastic deformation in the cement, our initial thermoplastic analysis with the Abaqus software indicated that such deformation is unlikely to cause debonding between the cement and casing.