Effect of Caprock Relative Permeability on Co2 Flow through it

Abstract

Geologic carbon storage is needed to meet the climate goal of limiting global warming to 1.5 ºC. Injecting in deep sedimentary formations brings CO2 to a supercritical state, yet less dense than the resident brine making it buoyant. Therefore, the assessment of the sealing capacity of the caprock lying above the storage reservoir is of paramount importance for the widespread deployment of geologic carbon storage. We perform laboratory-scale supercritical CO2 injection into a representative caprock sample and employ numerical simulations to provide an in-depth understanding of CO2 leakage mechanisms. We explore the effect of relative permeability curves on the potential CO2 leakage through the caprock. We show that capillary breakthrough is unlikely to take place across a non-fractured caprock with low intrinsic permeability and high entry pressure. Rather, CO2 leakage is dominated by the intrinsically slow molecular diffusion, favoring safe storage of CO2 over geological time scales.