Experimental Investigations of CO2 Solubility and Variations in Petrophysical Properties due to CO2 Storage in Carbonate Reservoir Rocks

The carbon dioxide (CO₂) sequestration and storage in aquifers and depleted oil and gas reservoirs is eminently a feasible solution to provide substantial cut in overall emission into the atmosphere. The current need is to understand the factors affecting the CO₂ sequestration potential and capacity of particular formation/reservoir.

The purpose of this study is to investigate the CO₂ storage in carbonate reservoir rocks under different conditions of pressure and temperature. Two groups of experiments were undertaken including; (1) investigating the CO₂ solubility under different brine salinities, and different pressure and temperature conditions, and (2) studying the effect of CO₂ storage time interval on porosity and permeability of carbonate reservoir rocks. Core storage experiments were undertaken using actual and similar core samples saturated with 25, 000 ppm NaCl brine. The potential of the CO₂ storage capacity and variations in porosity and permeability are evaluated and quantified.

The results showed that solubility of carbon dioxide decreases with increase in brine salinity and/or temperature. The increase of pressure causes a decrease in carbon dioxide solubility. In addition, the effect of temperature on carbon dioxide solubility diminishes above 120 °F and 4,000 psi pressure. The results also indicated that storage of carbon dioxide increases the petrophysical properties of porosity and permeability of carbonate rocks when the storage period is more than 150 days. On the other side, the CO₂ storage for short time < 7 days causes reduction in porosity and permeability of carbonate reservoir rock.

The application of the attained results of this study is expected to have good impact on design storage process of carbon dioxide, validation of developed mathematical models, and improving our understanding of the process.