Convective-reactive transport of dissolved CO2 in fractured-geological formations

Abstract

Carbon dioxide (CO2) storage in geologic formations is an attractive means of reducing greenhouse gas emissions. The main processes controlling the migration of CO2 in geological formations are related to convective mixing and geochemical reactions. The effects of heterogeneity on these coupled processes have been widely discussed in the literature. Recently, special attention has been devoted to fractured geological formations that can be found in several storage reservoirs. However, existing studies on the effect of fractures on the fate of CO2 neglect the key processes of geochemical reactions. This work aims at addressing this gap. Based on numerical simulations of a hypothetical reservoir, we explore the effect of fracture properties and topology on the domain's storage capacity at different rates of CO2 mineral dissolution. It is found that the fractures not only can help the mixing convection and reaction process in the domain but also may play a restrictive role in entering dissolved CO2 and hinder the plume fingers from growing. The hypothetical case is relevant in providing preliminary understanding but can show varying degrees of geological realism. For more representative geology, we investigate the migration-dissolution of buoyant CO2 on a large-scale outcrop of a volcanic basalt rock formation. The results show that neglecting thin fractures can significantly affect the predicted amount of trapped CO2. The storage capacity is more sensitive to heterogeneity at low dissolution rates. The findings are useful for the management of CO2 sequestration in fractured domains.