资源环境科技发展态势分析平台

Geological carbon storage (GCS) involves unstable drainage processes, the formation of patterns in a morphologically unstable interface between two fluids in a porous medium during drainage. The unstable drainage processes affect CO₂ storage efficiency and plume distribution, and can be greatly complicated by the mixed‐wet nature of rock surfaces common in hydrocarbon reservoirs where supercritical CO₂ (scCO₂) is used in enhanced oil recovery. We performed scCO₂ injection (brine drainage) experiments at 8.5 MPa and 45 °C in heterogeneous micromodels, two mixed‐wet with varying water‐ and intermediate‐wet patches, and one water‐wet. The flow regime changes from capillary fingering through crossover to viscous fingering in the micromodels of same pore geometry but different wetting surfaces at displacement rates with logCa (capillary number) increasing from −8.1 to −4.4. While the mixed‐wet micromodel with uniformly distributed intermediate‐wet patches yields ~0.15 scCO₂ saturation increase at both capillary fingering and crossover flow regimes (–8.1≤logCa≤ −6.1), the one heterogeneous wetting to scCO₂ results in ~0.09 saturation increase only at the crossover flow regime (−7.1 ≤logCa≤ −6.1). The interconnected flow paths in the former are quantified and compared to the channelized scCO₂ flow through intermediate‐wet patches in the latter by topological analysis. At logCa> −6.1 (near well), the effects of wettability and pore geometry are suppressed by strong viscous force. Both scCO₂ saturation and distribution suggest the importance of wettability on CO₂ storage efficiency and plume shape in reservoirs, and capillary leakage through caprock at GCS conditions.