EOS Modeling and Experimental Observations of Three-Hydrocarbon-Phase Equilibria

Abstract

Summary An equation-of-state (EOS) fluid characterization has been developed to model three-hydrocarbon-phase equilibria as part of the enriched-gas EOR research program for the Kuparuk hydrocarbon miscible flood on the Alaskan North Slope. Laboratory experiments with Kuparuk reservoir oils and miscible injectants have identified an apparent second equilibrium liquid that is heavier than the original oil and macroscopically reversible. A three-phase EOS fluid characterization was developed to match both two- and three-phase experimental data by use of a modified Peng-Robinson EOS. Experimental observations identified a relationship between the third phase and the oil's pentane-insoluble fraction. The characterization uses a total of 16 components, with the heaviest two approximating the pentane-soluble and pentane-insoluble portions of the C36+ fraction. The properties of these heavy pseudocomponents control the development and behavior of the heavy phase. The EOS fluid characterization was used to study three-phase, enriched-gas-drive displacement mechanisms. For the Kuparuk fluids, a condensing/vaporizing displacement mechanism is predicted in a three-phase environment. Reservoir-condition micromodel displacements were conducted to observe the phase-behavior and displacement mechanisms during Kuparuk enriched-gas displacements. Micromodel observations are consistent with a near-miscible condensing/vaporizing mechanism and qualitatively agree with EOS predictions.