Density measurement and equal density temperature of CO₂+brine from Dagang — formation from 313 to 363 K

Abstract

Densities of CO₂+Dagang — formation brine solution were measured by a magnetic suspension balance (MSB) in the pressure range from (10 to 18) MPa, at the temperatures from (313.15 to 363.15) K and CO₂ mass fractions at 0, 0.0101, 0.0198 and 0.0299. The experimental results revealed that the solution densities increased linearly with the increasing pressure and CO₂ concentration, while decreasing with the increasing temperatures in the experimental range. When the temperature increased from (313.15 to 363.15) K, the slopes of the densities versus (vs.) CO₂ mass fractions decreased from (0.193 to 0.106) g·cm⁻³. A correlation equation was developed based on thermodynamic theory and experimental data. The absolute average deviation between the correlation equation and the experimental data was 0.05%, and the maximum deviation was 0.37% for the density of CO₂+water/brine solution in common geological storage conditions. According to the density of CO₂ — free brine and apparent molar volume of CO₂ in brine, the equal density temperature (T _e ) of CO2+Dagang brine solution was obtained at 464.67 K when pressure is 10MPa, which means that the density of brine dissolved with CO₂ will be less than that of CO₂-free brine when the temperature is higher than 464.67 K at 10MPa. In this work the formation temperature of the Dagang oilfield reservoir is from 313.15 K to 363.15 K, which is lower than the equal density temperature. Therefore, the safety of CO₂ storage in Dagang oilfield reservoir can be guaranteed.