Experiments of CO2 Solubility in the Synthetic Brine from the Erdos Basin, China

Abstract:

Solubility trapping of CO₂ in saline aquifers is accepted to be the promising method in terms of carbon capture and storage (CCS). CO₂ solubility at geological sequestration conditions is of great significance in evaluating the carbon capture potential of brine formation. Unfortunately, most CO₂ solubility studies focus mainly on single-salt solutions, and only sparse literature exist for the data of CO₂ solubility in aqueous solutions containing the mixture of K⁺, Na⁺, Ca²⁺ and Mg²⁺. To fill the research gap, an experimental investigation on the CO₂ solubility in the synthetic brine is carried out. The samples were extracted through the injection wells of the Shenhua Carbon Capture and Storage project in the Erdos Basin located in northern China. The proportion of K⁺, Na⁺, Ca²⁺ and Mg²⁺ was determined by chemical analysis of the samples in the aquifers. The synthetic brine is used in this study, and the experimental process were improved to lower the risk of penetration of the supercritical fluid. Solubility data were measured over the temperature and pressure ranges of 318-348 K and 8-11 MPa. In the range studied, the average absolute deviation of CO₂ solubility between literature and experimental results was 2.7%, and the maximum absolute deviation was less than 5.4%. Krichevsky-Kasarnovsky (KK) equation was established to analyze the experimental data and the effect of different ions on CO₂ solubility was quantified using an optimization process. The liner fit between the CO₂ solubility and mixed ion concentration is satisfied with correlation coefficient of 0.91. The proposed model and experimental data therefore possess broad adaptability to geological carbon storage. This ambiguity in the mechanism of the ion effect drives our efforts toward a better understanding of the factors controlling CO₂ solubility in formation brine.