Effect of Supercritical CO₂ and Thermal Loading Cycles on Class G Well Cement Properties

In carbon dioxide (CO₂) capture and storage (CCS) technology, one of the goals is to prevent the injected CO₂ from leaking back into the atmosphere. The leakage paths include fractures on the cement sheath sealing the injection well and/or reactivated faults going through the caprock. During a batch-wise injection of CO₂, the wellbore is submitted to thermal loading cycles. After injection, the near-well materials, including cement sheath, are exposed to a CO₂-rich environment, especially in the vicinity of the reservoir. These thermal cycles (TC) and exposure environment can affect the properties of the sealing material like cement and create leakage paths. Portland G cement samples were submitted to TC and exposed to a supercritical CO₂ environment, respectively. The results show that after submitting to more than 100 TC, the strength of the cement sample can decrease by 40% and its Young's modulus by 20%. On the other hand, after exposure to supercritical CO₂ for 52 days, the strength of the cement can increase up to 170% and its Young's modulus up to 25%, depending on the cement slurry formulation.