Measurement and Modeling of CO₂Solubility in Natural and Synthetic Formation Brines for CO₂Sequestration

Abstract

CO2 solubility data in the natural formation brine, synthetic formation brine, and synthetic NaCl+CaCl2 brine were collected at the pressures from 100 to 200 bar, temperatures from 323 to 423 K. Experimental results demonstrate that the CO2 solubility in the synthetic formation brines can be reliably represented by that in the synthetic NaCl+CaCl2 brines. We extended our previously developed model (PSUCO2) to calculate CO2 solubility in aqueous mixed-salt solution by using the additivity rule of the Setschenow coefficients of the individual ions (Na(+), Ca(2+), Mg(2+), K(+), Cl(-), and SO4(2-)). Comparisons with previously published models against the experimental data reveal a clear improvement of the proposed PSUCO2 model. Additionally, the path of the maximum gradient of the CO2 solubility contours divides the P-T diagram into two distinct regions: in Region I, the CO2 solubility in the aqueous phase decreases monotonically in response to increased temperature; in region II, the behavior of the CO2 solubility is the opposite of that in Region I as the temperature increases.

Modeling of CO2 solubility in single and mixed electrolyte solutions using statistical associating fluid theory

“…Figure 12 shows the CO 2 solubility in synthetic brine A (I =1.712 mol/kg). Despite some minor underestimation at 423 K, the solubilities predicted by the model are in close agreement with experimental data (Zhao et al 2015c). Zhao et al (2015c) claimed that the mixed NaCl + CaCl 2 solution can be used as a substitute for studying CO 2 solubility in synthetic formation brine provided that the ionic strengths are the same.…”

“…Despite some minor underestimation at 423 K, the solubilities predicted by the model are in close agreement with experimental data (Zhao et al 2015c). Zhao et al (2015c) claimed that the mixed NaCl + CaCl 2 solution can be used as a substitute for studying CO 2 solubility in synthetic formation brine provided that the ionic strengths are the same. A comparison between Figures 9 and 12 shows that the calculated CO 2 solubilities in mixed NaCl + CaCl 2 solution are indeed very similar to those in synthetic brine A.…”

“…The performance of the SAFT2-KMSA model is further tested by considering CO 2 solubities in synthetic brines. We studied two sets of synthetic brines, namely A and B, whose CO 2 solubities were recently measured by Zhao et al (2015c). These synthetic brines contain 7 salt species including NaCl, KCl, CaCl 2 , MgCl 2 , Na 2 SO 4 , NaBr and SrCl 2 , and the ionic strength are 1.712 mol/kg and 4.984 mol/kg, respectively.…”

“…The satisfactory prediction of CO 2 solubilities in these complex synthetic brines suggests that the model parameters are transferrable, and the proposed SAFT2-KMSA model is predictive. Symbols are experimental data (Zhao et al 2015c) and lines are SAFT2-KMSA predictions. Symbols are experimental data (Zhao et al 2015c) and lines are SAFT2-KMSA predictions.…”

“…Liu et al (2011a) studied the CO 2 solubility in mixed NaCl + KCl + CaCl 2 solutions. Recently, Zhao et al (2015c) studied the CO 2 solubility in natural and synthetic formation brines, and concluded that the CO 2 solubility in synthetic formation brines may be represented by that in mixed NaCl + CaCl 2 solutions.…”