Interaction of water and supercritical carbon dioxide (ScCO2) with rock and joints

Reservoir stimulation by hydraulic fracturing has become a superior technique by injecting high-pressure fluid into deep rock to initiate fractures, creating new fluid paths to improve oil and gas extraction. Water is the primary fluid used in hydraulic fracturing and has demonstrated advantages over the decades in enhancing reservoir permeability. While water is the most common fluid used in hydraulic fracturing, its use presents several significant limitations. Chief among them is the intense demand on local freshwater supplies, which can exacerbate water scarcity and compete with agricultural and municipal needs in arid regions. Furthermore, the flowback of contaminated water -containing dissolved salts, heavy metals, and naturally occurring radioactive materials -poses serious risks of soil and groundwater pollution if not properly managed. Finally, the disposal of this produced water through deep-well injection has been conclusively linked to induced seismicity, or human-caused earthquakes, creating geological instability. These limitations encourage the search for alternative fluids, such as supercritical carbon dioxide (ScCO 2 ). This paper employed a 2D fully coupled hydromechanical finite-discrete element method (FDEM) to study the performance of water and ScCO 2 in intact and jointed rocks. Important factors, including flow rate, in-situ stress magnitude, and fluid viscosity, are assessed for both the fluid and the results, and the results are compared with respect to the fluid-driven fracture pattern and breakdown pressure. The results confirm the extraordinary performance of ScCO 2 compared to water. ScCO 2 penetrates easily into rock grains and joints, easily dilates them, and generates fracture branching and long fractures. Moreover, breakdown pressures are lower than those of water, making it a preferred alternative to enhance permeability with less fluid energy.