Advanced Geochemical Signatures for Monitoring CO2 Fate and Behavior

Abstract Carbon Capture and storage (CCS) technology represents a critical strategy for mitigating greenhouse gas emissions and achieving net-zero targets. Despite the promise of the various global technologies and tracer monitoring methods to evaluate the fate of injected CO2 in subsurface environments, substantial obstacles remain, particularly in terms of cost, regulatory compliance, and the scalability of these solutions. This study presents an experimental geochemical investigation aimed at stimulating the injectivity and storage capabilities of CO2. The approach was mixing two end-members at different rates; reservoir native CO2 (δ13C baseline measured average equal to −3.5‰) and injected CO2 with δ13C value equal to −10.1‰. The stable isotopic compositions of the gas samples were measured by GC-IRMS. International gas standards are injected prior to sample analysis to check accuracy, and the precision for daily runs must be ± 0.2‰ for carbon isotopes. The results were obtained from 30 gas samples representing 3 well scenarios with variable CO2 concentrations and compositions. The samples contain variable mixing rates of injected and native CO2; therefore, they were divided into three groups as A, B, and C, based on their δ13C- CO2 values. The average carbon isotopic compositions of CO2 for group A, group B, and group C are −9.7‰, −4.5‰, and −2.8‰, respectively. Their associated average CO2 concentration (mol%) for the three groups are 91%, 19%, and 46%, respectively. Mass-balance calculations were used to quantify the proportion of injected CO2 contributed to the received samples, assuming no isotopic fractionation affected δ13C-CO2. The produced gases from group A, group B, and group C contain 83.8%, 2.6%, and 7.95% of the injected CO2, respectively. The findings of this study are pivotal for enhancing our understanding of optimal zones for CO2 injectivity and storage. The findings indicate that carbon isotopic analysis is a robust method for monitoring the movement and fate of CO2 in complex subsurface environments, providing valuable insights for CCS initiatives.