Modeling of gas-liquid two-phase flows in a natural rock fracture-Application to carbon dioxide sequestration

Geologically sequestration of carbon dioxide (CO2) in brine-filled, subsurface formations has emerged as an effective approach to mitigate climate change. Within the low permeability subsurface rocks, there are fractures that act as natural fluid conduits. Therefore, understanding how CO2 moves when injected into an initially saturated rock fracture is critical for predicting carbon dioxide transport within fractured rocks.

Our study examined gas-liquid flow through models of rock fractures using a computational modeling approach. First, the Brown method was used to numerically generate a realistic three-dimensional rock fracture geometry with random roughness. Next, the fracture geometry was converted into a numerical mesh for gas-liquid flow calculations using the finite-volume solver ANSYS-FLUENT and the volume-of-fluid (VOF) method.

The simulation results for the case of a constant rate injection of CO2 into the initially water-saturated fracture were evaluated and presented for a range of conditions. The invading gas moved quickly, covering the large-aperture regions of the fracture. The effects of injection rate and interfacial surface tension between gas and liquid were studied. Relative permeability curves were developed to describe the gas-liquid flows in fracture. These permeability curves can be used in reservoir-scale discrete fracture models to predict CO2 motion within fractured geological formations.