CO2 SOLUBILITY IN WATER AND BRINE UNDER RESERVOIR CONDITIONS

Abstract

The reference Henry's constant was determined from 110 solubility data found in the literature for the CO₂/H₂O system over a temperature range of 298 to 523 K and a pressure range of 3.40 to 72.41 MPa. Since the Krichevsfcy-llinskaya equation was used to model the system, a correlation for the A parameter was also developed. In addition to the Krichevsky-Ilinskaya equation, another two-parameter correlation for the solubility of carbon dioxide in water was obtained by using the Krichevsky-Kasarnovsky equation. The reference Henry's constant and partial molar volume of carbon dioxide at infinite dilution were treated as adjustable parameters. The calculated values of the partial molar volume at infinite dilution did not correspond to experimentally determined values found in the literature. Therefore, a third correlation for the reference Henry's constant was obtained by using the Krichevsky-Kasarnovsky equation in conjunction with the correct values of the partial molar volume. This one parameter (Henry's constant) model did not fit the experimental data as well as the two-parameter models. The decreased solubility of CO₂ in brine was accounted for empirically by a single factor correlated to the weight percent of dissolved solids. A literature data set of 167 solubilities, with a temperature range of 298 to 523 K and a pressure range of 3.0 to 85.0 MPa, was used to develop this correlation. A wide scatter of data characterizes this correlation, which relates the CO₂ solubility in brine to the CO₂ solubility in water at the same temperature and pressure. The correlation is designed for applications in which the determination of concentrations of individual ions is impractical and the implementation of only one additional parameter is desirable, such as the use of compositional simulators to model miscible displacement in the petroleum industry. These correlations can be easily implemented into reservoir simulation calculations to account for the effects of CO₂ solubility in brine. These effects are often ignored even though they can have dramatic effects on the performance of the CO₂ enhanced oil recovery process. The correlations presented in this paper for the Henry's constant and the effect of dissolved solids can adequately account for these CO₂ solubility effects.