Analysis of CO₂ endpoint relative permeability and injectivity by change in pressure, temperature, and phase in saline aquifer

Carbon dioxide capture and geological storage are considered to be imperative practical means for reducing greenhouse gas emissions into the atmosphere. Among geological formations for carbon dioxide capture and geological storage, deep saline aquifer is tracked as a key site due to its huge potential and common occurrence when compared to oil and gas reservoirs. But, the two-phase behavior of CO₂ accompanied with water formation under conditions equivalent to geological storage are mostly unknown. In this study, relative permeability experiments have been conducted to measure the end-point relative permeability of CO₂ and investigations have been carried out to calculate injectivity using the relative permeability. In CO₂ and water system, the injectivity is the function of the CO₂ endpoint relative permeability. An experimental apparatus for CO₂-water relative permeability was designed and experiments were carried out under six different temperatures varying from 70°F to 120°F, while the cell pressure was varied from 500 to 1,300 psi for every respective temperature. From the results, it was evident that, in general, the endpoint relative permeability of carbon dioxide increases with decrease in viscosity ratio, while the endpoint relative permeability in the transition region between gas and supercritical decreases even with decreasing viscosity ratio. Also, based on the sensitivity studies carried out by varying pressure and temperature, it was experimentally confirmed that porous and permeable aquifers at a minimum depth of more than 800 m are the most appropriate storage sites.