The critical points of CO2-H2O, NaCl-H2O and CO2-NaCl-H2O fluid mixtures were measured by observing the vanishing and appearance of the meniscus by using the visible-type autoclave. The critical points of CO2-H2O and NaCl-H 2O fluids shift linearly with the variation in ion concentrations. The general tendency of the critical point shifting of H2O-NaCl- CO2 multi-component fluid was similar to the H2O-CO 2 fluid. However at higher NaCl concentrations, the variation in the critical point was higher for higher CO2 concentrations. The above phenomenon is believed due to the interaction of ion or ions and water molecule that exists in the fluid.
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