Wettability impact on supercritical CO 2 capillary trapping: Pore‐scale visualization and quantification

How the wettability of pore surfaces affects supercritical (sc) CO 2 capillary trapping in geologic carbon sequestration (GCS) is not well understood, and available evidence appears inconsistent. Using a high‐pressure micromodel‐microscopy system with image analysis, we studied the impact of wettability on scCO 2 capillary trapping during short‐term brine flooding (80 s, 8–667 pore volumes). Experiments on brine displacing scCO 2 were conducted at 8.5 MPa and 45°C in water‐wet (static contact angle θ = 20° ± 8°) and intermediate‐wet ( θ = 94° ± 13°) homogeneous micromodels under four different flow rates (capillary number Ca ranging from 9 × 10 −6 to 8 × 10 −4 ) with a total of eight conditions (four replicates for each). Brine invasion processes were recorded and statistical analysis was performed for over 2000 images of scCO 2 saturations, and scCO 2 cluster characteristics. The trapped scCO 2 saturation under intermediate‐wet conditions is 15% higher than under water‐wet conditions under the slowest flow rate ( Ca ∼ 9 × 10 −6 ). Based on the visualization and scCO 2 cluster analysis, we show that the scCO 2 trapping process in our micromodels is governed by bypass trapping that is enhanced by the larger contact angle. Smaller contact angles enhance cooperative pore filling and widen brine fingers (or channels), leading to smaller volumes of scCO 2 being bypassed. Increased flow rates suppress this wettability effect. scCO 2 trapping increases as wettability shifts toward less water‐wetting is clearly demonstrated in micromodel experiments The scCO 2 trapping process is governed by bypass trapping that is enhanced by larger contact angles Laboratory experiments and simulations need to be run at sufficiently slow flow rates to represent reservoir behavior