Upscaled Models for CO2 Migration in Geological Formations with Structural Heterogeneity

Geological carbon sequestration involves large-scale CO2 migration and immobilization within geometrically heterogeneous storage formations. Recent modeling studies have shown that structural features along the upper boundary of a storage formation can significantly decrease updip CO2 migration speed and increase structural trapping. This impact depends on caprock roughness, which can be present at different spatial scales--from seismic-resolution features such as domes, traps, and spill points to centimeter-scale rugosity observed at outcrops. The ability to resolve all relevant features within large-scale domains is not always practical, and thus upscaled modeling approaches may be required. We propose an alternative modeling approach, the VE model, which is based on the vertical equilibrium assumption. This type of simulator is well suited for modeling CO2 migration in gravity-dominated systems. The Utsira Formation is one such system due to the strong buoyancy effects are observed in the seismic data. We use 4D seismic data and our VE modeling tool to understand the physical parameters that control CO2 migration in the Utsira. Given the uncertainty in some important parameters--CO2 density, porosity, and topography of the top Utsira--we determine the range of uncertainty in CO2 and rock properties that is supported by the data.