Theoretical study of brine secondary imbibition in sandstone reservoirs: Implications for H2, CH4, and CO2 geo-storage

Abstract

In gas geo-storage operations, the injected ex-situ gas will displace the in-situ formation brine and partially occupy the porous space of the target rock. In case of water-wet rock, the displaced formation brine re-imbibes into the in-situ porous space so that the system reaches thermodynamic equilibrium. This process, referred to as ‘secondary imbibition (SI)’, has important influences on the final gas geo-storage performance, as it determines gas loss (e.g., due to capillary forces, “residual trapping”) and injection/withdrawal efficiency. Herein, a fundamental analysis of this SI process in a single capillary tube was performed.Thus, the modified Lucas-Washburn equation was applied to a theoretical analysis, and the effects of gas type, formation depth, organic acid concentration, carbon number, and silica nanofluid on the SI dynamics were assessed. It was found that the SI rate depended on gas type following the order H2, CH4, CO2, and that the SI rate increased with formation depth for H2 and CH4, while it decreased for CO2. Further, the adsorbed organic matter reduced the SI rate, while the silica nanofluid aging accelerated the SI rate.These insights will promote fundamental understanding of gas geo-storage processes. This work thus will provide useful guidance on gas storage capacity optimization and containment security evaluation.