Coupled multiphase flow and transport simulation to model CO2 dissolution and local capillary trapping in permeability and capillary heterogeneous reservoir

Abstract

Deep CO2 storage reservoirs show a wide range of heterogeneous structures across different scales. Here, we show how high-resolution heterogeneity in both permeability and capillary entry pressure control dissolution and local capillary trapping of supercritical CO2 (ScCO2). Prior works mainly considered homogeneous reservoirs or simplified heterogeneity with horizontal and fixed capillary transition zones. Most of those studies ignored simultaneous free-phase ScCO2 spreading and solutal fingering. To advance understanding of heterogeneity effects, we have performed two-dimensional numerical simulations for ScCO2 injection into the middle of a storage reservoir. We have computed metrics including the spatial plume moments to compare the dissolution trapping and spreading of ScCO2 during the injection and post-injection period for different variances and correlation lengths of log-normal permeability and capillary entry pressure fields. The results show that the second-order spatial moment of the ScCO2 saturation field in the horizontal direction decreases by 10% as the permeability variance increases from 0.1 to 3.0. But it decreases by 50% as the capillary entry pressure variance becomes 1.1. For higher capillary entry pressure variance, the ratio of dissolved CO2 mass to free-phase ScCO2 mass decreases, showing higher local capillary trapping. The vertical distance between the centers of mass of the ScCO2 and dissolved CO2 plumes (representing the downward flow of dissolved CO2 through solutal fingering) is greater for heterogeneous reservoirs.