Summary
The design of miscible CO2 recovery methods and the evaluation of laboratory CO2 coreflood and pilot field studies require knowledge of the phase behavior encountered in such processes and the ability to make reliable predictions. Because of the complexity of CO2/hydrocarbon phase behavior, experimental measurements are necessary as a basis from which to develop an understanding. In this paper, measured phase equilibria and volumetric properties are reported for several west-Texas-reservoir-oil/CO2 systems. Reservoir oils studied were from the San Andres, Grayburg, and Devonian Chert formations. Both static (single-contact) and multiple-contact measurements have been conducted in a visual fluid property cell. Static data cover a wide range of CO2 compositions and provide a general understanding of CO2/reservoir-oil phase behavior. Multiple-contact measurements in which the CO2-rich phase is repeatedly contacted with recombined reservoir oil (oil cycling) simulate phase behavior occurring at the flood front. Multiple-contact measurements in which the oil-rich liquid phase is repeatedly contacted with pure CO2 (CO2 cycling) simulate the phase behavior exhibited by residual oil near a CO2 injection well. The multiple-contact data cover narrow compositional paths encountered in displacement processes and serve as a basis for equation-of-state (EOS) evaluation. Phase behavior trends common to all systems are discussed.