Subsurface storage of CO2 is a crucial tool in achieving a net-zero emissions transition. Despite significant progress in carbon capture, utilization, and storage techniques and deployments, current CO2 storage rates are still below target. As a result, all potential options must be explored. This study investigates the feasibility of CO2 storage in depleted unconventional oil and gas reservoirs, with a focus on estimating capacity based on production data for major US basins, conducting rate transient analysis for injectivity and capacity of a single well, and examining microscale mechanisms of CO2-water-oil displacement. The study also discusses fault and fracture stability assessment and monitoring techniques for CO2 injection and storage. The differences between CO2 storage in unconventional reservoirs and saline aquifers or conventional reservoirs are highlighted, as are the similarities and differences between CO2 injection/storage and hydrocarbon production in unconventional reservoirs. The findings and conceptual framework in this paper could lay a robust foundation for future research and practical implementation.
Carbon capture, utilization, and storage (CCUS) is a crucial aspect of the global energy transition, and it has the potential to contribute to one third of the emissions reduction necessary to achieve the global net-zero emission targets by 2050 (Flowers, 2022). In recent years, significant advancements have been made in CCUS and carbon dioxide removal technologies, and pilot-and field-scale deployments in saline aquifers and conventional reservoirs have shown promise. Despite these developments, the current rate of CO2 storage is only around 56 Megatons (MT), which is far below the global target of ∼170 Gigatons (GT) by 2050, requiring storage of 5–8 GT per annum (Fankhauser et al., 2022; Martin-Roberts et al., 2021; Williams et al., 2021). According to current deployment rates, it is projected that the capacity for CO2 storage by 2050 will be approximately 700 MT per year, which is just 10% of the required amount (Martin-Roberts et al., 2021). Therefore, it is imperative to explore every potential option to maximize the storage of CO2 in vast subsurface reserves.