Assessing Subsurface Gas Storage Security for Climate Change Mitigation and Energy Transition

Subsurface gas storage is crucial for achieving a sustainable energy future, as it helps to reduce CO2 emissions and facilitates the provision of renewable energy sources. The confinement effect of the nanopores in caprock induces distinctive thermophysical properties and fluid dynamics. In this paper, we present a multi-scale study to characterize the subsurface transport of CO2, CH4, and H2. A nanoscale-extended volume-translated Cubic-Plus-Association equation of state was developed and incorporated in a field-scale numerical simulation, based on a full reservoir-caprock suite model. Results suggest that in the transition from nanoscale to bulk-scale, gas solubility in water decreases while phase density and interfacial tension increase. For the first time, a power law relationship was identified between the capillary pressure within nanopores and the pore size. Controlled by buoyancy, viscous force and capillary pressure, gases transport vertically and horizontally in reservoir and caprock. H2 has the maximum potential to move upward and the lowest areal sweep efficiency; in short term, CH4 is more prone to upward migration compared to CO2, while in long term, CH4 and CO2 perform comparably. Thicker caprock and larger caprock pore size generally bring greater upward inclination. Gases penetrate the caprock when CH4 is stored with a caprock thickness smaller than 28 m or H2 is stored with a caprock pore size of 2-10 nm or larger than 100 nm. This study sheds light on the fluid properties and dynamics in nanoconfined environment and is expected to contribute to the safe implementation of gigatonne scale subsurface gas storage. Aiming at the ambitious targets of net-zero emission and global energy transition, effective technologies need to be developed and deployed with huge efforts. Subsurface gas storage is expected to play a critical role in reducing CO2 emission and providing large-scale renewable energy. However, unforeseen gas leakage can cause potential environmental risks and energy efficiency concerns. Despite its importance, the mechanisms governing gas transport and distribution within caprocks, particularly under nanoconfinement conditions, are poorly understood. From nano-scale and bulk-scale thermodynamic properties predictions to field-scale numerical simulations, this work carried out a comprehensive multi-scale analysis to evaluate the storage security of CO2, CH4, and H2. Relationships between VLE, phase density, interfacial tension, capillary pressure and pore size, temperature, pressure and wettability were discussed, offering novel perspectives on the mechanisms governing gas leakage. Furthermore, loss potentials of different gases were compared and evaluated and the impacts of caprock thickness and pore size were examined, providing valuable insights for screening eligible storage sites. Overall, this work contributes to the development of secure and reliable gas storage techniques, supporting the goals of climate change mitigation and facilitating the transition to a net-zero energy future. A multi-scale analysis is carried out to assess the loss potential of CO2, CH4, and H2 during subsurface storage Migration and distribution characteristics of gases in the caprock are investigated Short-term and long-term gas storage security are analyzed and compared