Abstract

Solvent-leaching gravity drainage based processes have gained increasing interest for improving recovery from low-pressure heavy oil and bitumen reservoirs around the world. In these processes, injected solvent in the vapor phase diffuses and dissolves into the oil, hence mobilizing it by viscosity reduction. The mobilized oil drains into a production well under the influence of gravity and capillary forces. In this study, a comprehensive experimental program was conducted to systematically investigate the effects of capillarity and drainage height on stabilized drainage rates in a permeability range of 5.1-6.5D, which is similar to that of western Canadian heavy oil reservoirs. In addition to these experiments, separate investigations were undertaken to measure the capillary pressure of sand packs, as well as phase behavior properties of the oil-solvent system used in this study. The novel design of the experimental setup made it possible to eliminate the effect of pressure disturbances and forced displacement for the duration of the experiments (20-45 days), and investigate the interplay between capillarity and drainage height in the gravity-dominant system. It was found that the observed stabilized drainage rates per unit length of porous media (9.85×10−7-3.44×10−5 cm3/s/cm) are function of drainage height, specific pore surface area of porous media, and concentration of diffused solvent into the oil phase. A one-dimensional analytical model was adapted to calculate the diffusion coefficients for these experiments and develop a new correlation for the prediction of the effective diffusion coefficient in this process. Experimental results and modeling showed that molecular diffusion was the major drive for the mass transfer phenomena in higher capillarities. According to the developed correlation in this study, drainage height, capillarity, and solvent concentration in the oil phase play more important roles in mass transfer phenomenon than those observed in experiments conducted at high permeabilities (>200D).

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