Experimental and numerical studies of CO₂ injection into water-saturated porous medium: Capillary to viscous to fracture fingering phenomenon

Injection of anthropogenic carbon dioxide (CO₂) into deep saline geological formations is a possible long-term solution of removing CO ₂ from the atmosphere. The early injection of CO₂ into saline aquifer is known as drainage and can cause unstable fingers to extend into the saturated rock pores. In this work, the crossover from capillary invasion to viscous fingering to fracturing is studied. Experimentally, a vertical Hele-Shaw cell filled with micro-beads was set up to study different injection rates of gas invasion into saturated porous media. The visualized invasion patterns showed that the crossover from capillary to viscous to fracture can occur in the same vertical cell but at different heights due to gas bursts occurring at different overburden and pore pressures. Numerically, 2D simulations of the invasion using STOMP (Subsurface Transport Over Multiple Phases) overpredicted the width of fingers obtained experimentally due to the averaging process of the model.