Experimental investigation of gas permeability and flow behaviour in wellbore cements

The injection of CO₂ into underground formations is critical for enhancing hydrocarbon recovery and mitigating climate change through Carbon Capture and Storage (CCS) projects. In these operations, maintaining the integrity of wellbore cement—the primary barrier preventing CO₂ leakage—is essential for the success and safety of both active and abandoned wells. Any compromise in cement integrity could lead to CO₂ leakage, undermining injection efforts and posing serious environmental risks. Therefore, understanding CO₂ flow through wellbore cement is crucial. This study evaluates the structural characteristics and gas permeability of short-term cured Neat and lightweight cement under simulated bottomhole conditions, representing early-stage exposure to CO₂ after cementing operations. Samples were prepared following optimized API-standard procedures. XRD analysis quantified hydration levels, while CT scans and MICP tests provided insights into cement microstructure and pore size distribution, informing gas flow behavior during permeability testing. Experimental results showed significant differences between the two cements. Neat cement displayed a uniform, fracture-free matrix with ∼38 % porosity and a mean pore throat radius of 0.041 µm, resulting in low gas permeability (18–21 µD) and particularly low CO₂ permeability due to its higher density and adsorption properties. Lightweight cement, however, exhibited a fractured structure, higher porosity (46 %), and a smaller mean pore throat radius (0.011 µm), leading to much higher gas permeabilities (1.1–1.4 mD). These findings underscore the importance of cement type and microstructure in controlling CO₂ migration, emphasizing the need for optimized cement designs to ensure long-term well integrity in CCS applications.