Mechanical Evaluation of a Novel Cement Formulation used for Thermal Energy Storage Wells

High Temperature Reservoir Thermal Energy Storage (HT-RTES) is a promising solution for large-scale energy storage that can stabilize the electric grid, increase its flexibility, and provide energy on demand. Despite its advantages, the HT-RTES wells require a higher standard for cement integrity due to higher temperatures and thermo-mechanical stresses during injection and production. In this study, we provided a thorough mechanical investigation on the hydrophobic fly ash cenospheres (FCS) incorporated calcium aluminate cement, which exhibits a lower thermal conductivity compared to conventional oil and gas well cement to prevent heat losses. The cement was treated with superhydrophobic polymethylhydrosiloxane (PMHS). The compression tests were conducted under in situ high pressure high temperatures, with pressure reaching up to 10 MPa and temperature up to 180 °C. The findings revealed that the PMHS-treated specimens, after undergoing simulated thermo-mechanical stresses, showed an increase in cement compressive strength from 4.6-30 MPa to 6.1-33 MPa, an improvement in elastic modulus from 0.34-1.37 GPa to 1.1-3.3 GPa, and an enhancement in Poisson’s ratio from 0.07-0.15 to 0.1-0.33. Therefore, lightweight calcium-aluminate cement formulations with PMHS treated FCS could preserve its mechanical performance after subjecting to thermal shock. We further incorporated the measured properties into a fully coupled thermoporoelastic model for wellbore integrity analysis. Results show that the novel PMHS treated FCS could resist large range of pressure and temperature perturbations during heat injection and production. Overall, this novel formulation could be a promising solution to the durability of the HT-RTES wells.