Impact of microbial-rock-CO₂ interactions on containment and storage security of supercritical CO₂ in carbonates

Carbon Capture and Sequestration (CCS) has been widely adopted as a key technology to mitigate anthropogenic greenhouse gas emissions and to meet the 2050 net-zero carbon emission target. However, the long-term CO₂ storage security and potential leakage in geologic formations still pose a major concern to the commercial implementation and viability of CCS as an efficient and safe carbon-negative technology against climate change. Also, the long-term effectiveness of carbonate formations for carbon sequestration is poorly constrained due to the reactivity of carbonates with pore water when exposed to CO₂, the possible leakage paths that might develop, and potential consequences that could occur. Here, we examine CO₂ storage in carbonate formations and the possible leakage issues and explore a potential remediation technology for improving storage security in carbonate formations to mitigate CO₂ leakage and achieve long-term containment. In this study, samples from deep carbonate intervals are treated with cultured microbial media and/or supercritical CO₂ (ScCO₂). These treatments are complemented with pre- and post-treatment geomechanical tests, permeability measurements, Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) analyses to assess mechanical, chemical, and microstructural responses of carbonates exposed to ScCO₂ in the presence or absence of microbial media in the pore volume. The results indicate that, in the absence of sufficient post-injection remediation, the long-term integrity of CO₂ storage in carbonate reservoirs may be compromised by CO₂ leakage leading to environmental degradation. However, analyses of results suggest that coupling microbial treatment with CCS in carbonate reservoirs can potentially maintain long-term CO₂ storage security by moderately enhancing its mechanical strength and integrity. In tight carbonate samples, unconfined compressive strength is shown to increase +85% with Poisson's ratio decreasing by 32% and fracture toughness increasing +108%. In more porous carbonate samples, unconfined compressive strength increases +64%, Poisson's ratio decreases by 34%, and fracture toughness increases +130%, all relative to the same CO₂ saturation in carbonates without microbial media. Further, results show a post-microbial-CO₂ change in permeability, dissolution and reprecipitation of stronger minerals due to microstructural alteration and occlusion of leakage pathways. This study provides new insights into the viability of CCS in carbonate reservoirs with microbial treatment as an efficient technology against climate change and greenhouse gas emissions to prevent leakage of stored CO₂ and provide adequate long-term CO₂ storage retention.