Measurment And Modeling Of CO₂Solubility In Formation Brine

Disasters caused by over-discharged greenhouse gas (CO2, CH4et.al) have promptedthe strength of the significance for the CO2emission reduction. Implementation ofCO2storage underground in deep saline aquifers is recognized as the most promisingsolution responseing to greenhouse effect. Among all the geological formations (oiland gas reservoirs, deep saline aquifers, saturated brackish water or brine and coalseams), deep saline aquifers potentially process the largest storage capacity. Solubilitytrapping means that supercritical CO2(Temperature above31.4℃and pressure above7.38MPa)dissolving in the water of the formation. This mechanism accounts for90%of the estimated total carbon storage capacity.The concentration of common salt in brine formation can reach400g/L, and since K+,Na+, Ca2+and Mg2+is the most common ions in brine, it is of a wide range oftheoretical and practical significance to identify the effect of the of these ions on thesolubility of CO2. However, the effect of different types of ions on the solubility ofCO2has rarely been studied under high pressure conditions. Many CO2solubilitymodel only treat the valence electrons as the impact of different types of cations onthe solubility, but some experiments show that this position is not accurate. In order toobtain the solubility of CO2in brine, this paper will do the research in both theoreticaland experimental ways.In this study, based on the equation of state (EOS) and Krichevsky-Kasarnovsky,theoretical equation for CO2solubility is predicted by strike the fugacity of CO2insupercritical fluid phase and fugacity in the liquid phase to obtain CO2solubility overa temperature range of313-453K,5-48MPa, and ion concentration range of0-4mol/L (mixed ion concentration). Meanwhile, based on the volume analysis andchemical analysis method, the experimental investigation has been conducted for thedetermination of CO2solubility, wherein the volume analysis method applies for anew set of designed instrument by measuring the volume of gas escaping from thesystem to obtain the CO2solubility. This method overcomes the shortcomings ofinconveniences for the traditional autoclave sampling and the poor reproducibility ofthe experiment. Determination and comparison of the two groups of CO2solubility inCaCl2and MgCl2solution over a T-P range of40-70℃,0-20MPa. Besides， measurement of CO2solubility in synthesis brine of40-70℃,8-11MPa has beenconducted. Experimental results show that the change of CO2solubility in solutionscontaining different ions is relatively obvious. Krichevsky-Kasanovsky equation hasbeen utilized to analyze the effect of temperature and pressure, and the effect ofdifferent ions on the solubility is given a more reasonable explanation with the"salting out" effect.