Investigating the Impact of Caprock Morphology on CO2 Plume Migration and Trapping Mechanisms Using the MRST-CO2lab and ECLIPSE-Blackoil Codes.

One of the possible options to mitigate the climate change is sequestering anthropogenic carbon in the deep saline aquifers. When injected in the formation, due to the difference in buoyancy forces between the gas and the brine, the free phase CO2 is driven upwards and will eventually collect as a separate, thin layer beneath the caprock. Therefore, the structural geometry of this upper seal plays a significant role in the long-term CO2 plume migration and trapping behaviour. In practice, at the kilometre scale, there are considerable topography changes, and the caprock structure is identified by domes and anticlines. Researchers primarily use 3D numerical simulators to study the long-term behaviour of the CO2 plume. This study looks at the impact of the dipping and sinusoidal pattern between two strata on the storage process using a full 3D simulation as well as an upscaled model based on the vertical equilibrium (VE) assumption. The 3D simulation is performed using the ECLIPSE-blackoil and the MRST (MATLAB Reservoir Simulation Toolkit) is used for the VE approach. Under the VE assumption, the CO2 plume flow in 3D can be approximated in terms of its thickness to obtain a 2D simulation model, which significantly decrease the computational cost and avoids the discretization error caused by limited vertical resolution in a 3D model. Over the time period simulated, our observations of lateral migration showed that the CO2 and resident brine became quickly separated and formed two separate layers. To our knowledge, this is one of the first comparisons between the standard three-dimensional reservoir simulator and two-dimensional VE formulation for studying the impact of caprock morphology on CO2 storage.