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Experimental and theoretical techniques have been developed to quantify the behavior of alkaline water−heavy oil emulsion systems at high pressures and elevated temperatures. Experimentally, initial emulsions were prepared by agitating either sodium carbonate (Na 2 CO 3 ) solution or sodium hydroxide (NaOH) solution with heavy oil samples inside a visualized PVT cell. After being settled for a certain period of time, the phase volume of the in situ generated water-in-oil (W/O) emulsion was monitored, and the local water content distribution within each dual-emulsion system was measured. Experiments with the same composition and mixing condition, but with different settling times, were conducted to track the continuous water content distribution. Mathematically, two groups of population balance equations (PBEs) were modified and applied to quantify the phase behavior during the emulsion destabilization process with the consideration of coalescence, settling, and diffusion of the dispersed droplets as well as the mass transfer between emulsion phases. To quantify the mass transfer between the W/O and oil-in-water (O/ W) emulsion phases, the measured emulsion inversion point (EIP) was used as the interface boundary condition of the dualemulsion systems. Both the fixed-pivot technique and a semi-implicit finite difference approach were applied for discretizing the internal coordinate (droplet volume) and the external coordinates in time and space domains, respectively. By assuming the dispersed droplets as a log-normal distribution, the genetic algorithm (GA) was applied to optimize the coalescence efficiency by using the experimental measurements as well as the water droplet distribution in the W/O emulsion phase. Because of the corresponding changes of oil viscosity and interfacial tension (IFT), either an increase in temperature or a decrease in pressure leads to a smaller EIP and higher coalescence efficiency. As a weak alkali, Na 2 CO 3 facilitates the stabilization of the emulsion and inhibits the influence of higher temperatures, while NaOH solution−heavy oil systems achieve emulsion inversion more easily.

Summary Accurate quantification of phase behavior of solvent/heavy-oil/bitumen/water systems at high pressures and elevated temperatures is of high significance for the design of vapor extraction, cyclic solvent injection, expanding-solvent steam-assisted gravity drainage (ES-SAGD), and hot-solvent injection processes. The relevant experimental data and theoretical analyses are still insufficient for achieving a reliable model. This is especially true when the system temperatures approach or exceed the critical temperatures of the solvents used (i.e., when the solvent density is large enough). This study provides new experimental measurements of the phase behavior of propane (C3H8)/carbon dioxide (CO2)/heavy-oil/water systems at pressures up to 20 MPa and temperatures up to 432.3 K. More specifically, four feeds of C3H8/CO2/heavy-oil/water systems are used to conduct constant composition expansion (CCE) tests, during which the heights of the entire fluid system (i.e., total volume) and each phase are recorded at each pressure and temperature, respectively. Theoretically, a dynamic volume analysis (DVA) of the measured data is proposed for the first time to quantify each phase, provided that the assumption for vapor phase is valid and that the vapor and oleic phase densities can be accurately calculated. By tuning the binary interaction parameter (BIP) for solvent/heavy-oil pairs (denoted as BIPS−HO) to match the total volume, the height of the vapor/oleic (V/L) interface can be matched as well. By using the tuned BIPS−HO, the total volume and height of the V/L interface of C3H8/CO2/heavy-oil/water systems can be accurately predicted, no matter whether the solvent solubility in water is low (i.e., C3H8) or high (i.e., CO2). This DVA can be used to determine/evaluate the solvent solubility, saturation pressure/phase boundary, and phase volume/density accurately in a large temperature and pressure range. The newly proposed DVA method is also used to reproduce the experimental measurements collected from the literature, including phase-volume fractions, solvent solubility, and saturation pressure. In addition, the DVA method can serve as a tool to check whether the experimental measurements are reliable or not.