Flow-through Drying during CO2 Injection into Brine-filled Natural Fractures: A Tale of Effective Normal Stress

Injecting supercritical CO2 (scCO2) into brine-filled fracture-dominated reservoirs causes brine displacement and possibly evaporite precipitations that alter the fracture space. Here, we report on isothermal laboratory experiments on scCO2-induced flow-through drying in a naturally fractured granodiorite specimen under effective normal stresses of 5-10 MPa, where two drying regimes are identified. A novel approach is developed to delineate the evolution of brine saturation and relative permeability from fluid production and differential pressure measurements. Under higher compressive stresses, the derived relative permeability curves indicate lower mobility of brine and higher mobility of the scCO2 phase. The derived fractional flow curves also suggest an increase in channelling and a decrease in brine sweep efficiencies under higher compressive stresses. Finally, lowering compressive stresses seems to promote less water evaporation. Our experimental results assist in understanding the injectivity of single fractures and eventually of fracture networks during subsurface applications that involve scCO2 injection into saline formations.

Automated summary

Research indicates that injecting scCO2 into fractured reservoirs under high compressive stress reduces the mobility of brine and increases the mobility of scCO2 phase, leading to channeling and decreased brine sweep efficiency. Lowering compressive stress helps to decrease water evaporation.