Impact of geological heterogeneity, layer thickness and stress field on CO2 storage in continental flood basalts

Abstract

Continental flood basalts (CFBs) are widely considered as promising CO2 storage reservoirs because they contain reactive minerals resulting in a high rate of carbon mineralisation. However, only a few studies have explored the petrophysical and multiphase flow properties of vesicular basalt layers in relation to CO2 injection and storage at reservoir scale. Impact of variations in vesicular layer thickness in stacked CFB systems on pore pressure buildup, as well as the influence of different in-situ stress fields on geo-mechanical risks, remain largely underexplored. To answer these questions, a total of 90 flow simulations were conducted in two 3D reservoir domains to assess CO2 behaviour under pilot to industrial scale injection scenarios, for both supercritical-CO2 and CO2-enriched water. Results suggest that maximum residual gas saturation, near-wellbore permeability and porosity heterogeneity are key variables controlling residual trapping, pore pressure buildup and pore space utilization. Thinner layers were more sensitive to pressure buildup but offered better pore space utilization. Geo-mechanical analyses suggests that reverse-fault conditions with a moderate tectonic stress regime are safer in terms of rock stability. While CO2-enriched water injections pose lower geo-mechanical risk, supercritical-CO2 injection allows for a much higher CO2 storage capacity and higher pore space utilization.