Effects of Aqueous Solubility and Geochemistry on CO₂ Injection for Shale Gas Reservoirs

In shale gas reservoirs, CH₄ and CO₂ have finite aqueous solubilities at high-pressure conditions and their dissolutions in water affect the determination of the original gas in place and the CO₂ sequestration. In addition, the dissolution of CO₂ decreases the pH of connate water, and the geochemical reactions may thus occur in carbonate-rich shale reservoirs. The comprehensive simulations of this work quantify the effects of aqueous solubility and geochemistry on the performance CO₂ huff-n-puff process in shale gas reservoir. Accounting for the aqueous solubility of CH₄ increases the initial natural gas storage and natural gas production. The effect of the aqueous solubility of CO₂ enables to sequester additional CO₂ via solubility trapping. Considering the geochemical reactions, the application of the CO₂ huff-n-puff process causes the dissolution of carbonate minerals and increases the porosity enhancing the gas flow and the gas recovery. Incorporation of geochemistry also predicts the less CO₂ sequestration capacity. Therefore, this study recommends the consideration of aqueous solubility and geochemical reactions for the accurate prediction of gas recovery and CO₂ sequestration in shale gas reservoirs during the CO₂ huff-n-puff process.