An Analysis of the Linear Displacement of Oil by Gas-Driven Solvent

A method of calculation is presented for predicting the performance of a solvent extraction process. The process proposed involves the displacement of oil by a liquid solvent which is moved through the reservoir by a driving gas. The gas evaporates solvent at the point of first contact, and condenses the solvent vapor farther downstream. This condensation swells the oil and decreases its viscosity, thus making displacement of the oil easier. It has been predicted theoretically that 100 per cent recovery of oil is possible. A formula is derived which permits calculation of the minimum solvent requirement to secure complete oil recovery. Also derived are formulas for calculating the average residual oil saturation left when less solvent is used, and the flowing gas-liquid ratios emerging from the porous body. Appropriate material balance equations are presented to provide a check on the correctness of the derivations and the precision of the calculations. The solution of a typical gas-driven solvent problem requires a few hours' time on a medium-speed computing machine. Curves are given in the paper which illustrate the results obtained in the calculations. The theoretical results compare very favorably with experimental studies made on long cores. For a given quantity of injected solvent and a given throughput of gas in pore volumes, the displacement of oil is not very sensitive either to the pressure level employed, or to the type of sandstone. Introduction The recovery of oil by solvent extraction is currently receiving much attention. Part of this interest is no doubt due to the fact that oil recoveries up to 100 per cent may be obtainable in the contacted or swept portions of the reservoir.