Impact of 3D capillary heterogeneity and bedform architecture at the sub-meter scale on CO2 saturation for buoyant flow in clastic aquifers

During the post-injection and stabilization period of geological carbon sequestration, the primary forces governing CO2 migration and entrapment are capillarity and buoyancy, delineating a specific field of application for numerical flow models. In contrast with conventional modeling approaches that assume laminar viscous flow regime, a modified invasion percolation simulator is used to mimic the physics of fluid flow for vanishing pressure gradients. The current investigation extends a previous study simulating 2D CO2 invasion through stochastic and natural geologic models. Research presented here expands methods for addressing role of heterogeneity on fluid migration by quantifying the influence of 3D variability in threshold capillary pressure and bedform architecture on CO2 saturation. The goal is to develop a predictive method for volumetric storage capacity for buoyant flow conditions. Realistic sedimentary models are generated for eight common clastic facies with accurately represented bedform morphology. Resulting 3D models consist of matrix and lamina cells that are populated independently with probability density functions representative of sandstone lithologies with different grain sizes and sorting. Results from thousands of MIP simulations reveal saturation in the eight models to be a non-linear function that is primarily influenced by the contrast in threshold capillary pressures between matrix and lamina (observable lithologic heterogeneity), suggesting some predictive ability is achievable from common sedimentologic descriptors, although quantifying the independent effect of depositional architecture remains more difficult.