Fluid transport driven by geothermal gradient and its impact on the storage characteristics of CO2 hydrates

Abstract

Carbon capture and storage (CCS) is a crucial strategy for mitigating global warming. The long-term sequestration of CO₂ by storing it as hydrates in marine sediments represents a potentially viable solution. Notably, most marine sediments exhibit a geothermal gradient, which significantly affects hydrates’ formation characteristics and spatial distribution. This study examines the impact of the geothermal gradient on CO₂ migration and sequestration, focusing on primary and secondary injections. More than 50 % of the reservoir’s water remains unutilized after the secondary injection, but the final gas conversion differs by 10 %. The findings indicate that gas diffusion is the primary factor influencing the formation of hydrates. Furthermore, gas transport mechanisms differ between primary and secondary injections under the geothermal gradient. During primary injection, the gas migrates through the sediment in a sequence comprising top accumulation, rapid diffusion, and top accumulation. During secondary injection, heat is cycled back and forth through the reservoir along with the phase transition of CO₂. A comparison of the primary and secondary injection processes revealed a stepwise distribution of hydrate formation, with the highest yield occurring in low-temperature zones and the lowest in high-temperature zones. These findings contribute to a more nuanced comprehension of CO₂ storage within marine sediments.