Numerical study on the effects of fracture on density-driven flows in CO2 sequestration

Abstract

In this study, CO2 transport in density-driven flows within an ideal model of a fractured porous medium, which contains a single or two intersecting fractures, is investigated numerically. The study employs a multi-scale modeling in which the flow in the matrix is modeled by Darcy's law, while the flow in the fracture is modeled by the Navier–Stokes equations. Our study shows that a horizontal fracture minimally impacts CO2 distribution, and depending on its length, slightly reduces dissolved CO2 during sequestration by 1.5%–2.5%. Vertical fractures play a crucial role in redirecting CO2 movement within the matrix, guiding it toward the fractures and altering its original pathway. Notably, the observed oscillations of CO2-rich water between the interfaces of the vertical fracture highlight the flow consistency with the pore scale. The domain-scale circulation induced by the vertical fracture leads to a rapid increase in flux and dissolved CO2 mass, but early convection shuts down. The results demonstrate that a longer vertical fracture leads to earlier shut down of convection and a potential decrease in storage of over 11%. The flow behaviors observed in inclined fractures are akin to those in vertical fractures, as they disrupt the fingerlike structure of CO2 around the fracture, form the circulation around the fracture, and are accompanied by vortices at the top. Additionally, intersecting fractures can lead to dynamic interactions between the fractures, with high-angle fractures dominating mixing flow. Different fracture angle combinations minimally affect dissolution mass.