Experimental study of oil recovery from porous material by means of carbon dioxide flooding

Abstract

The increased demand for crude oil in the world and in particular in the United States has caused the oil industry to develop techniques to increase the recovery of crude oil from subsurface formations. One technique utilizing carbon dioxide has received considerable attention in the past decade. The published results of experiments and tests to determine the effectiveness of carbon dioxide are not in agreement as to the best procedure for using carbon dioxide nor as to the volume of crude oil that can be recovered. The purpose of this work was to study experimentally the effectiveness of carbon dioxide in displacing oil from porous media. A goal of the work was to determine the best method to utilize carbon dioxide and to predict the fraction of oil in reservoir rock that could be recovered by carbon dioxide. Sandstone cores containing crude oil and connate water were 'first flooded with water. Most reservoirs would be waterflooded prior to injecting carbon dioxide. Carbon dioxide was injected into some of the cores as a gas and into others dissolved in water. The displacements were conducted at reservoir pressure and at reservoir temperature. The fraction of oil recovered was measured. A light crude oil from West Texas and a heavy crude oil from East Texas were used in the experiments. At the completion of the displacement of oil try either carbon dioxide gas or carbonated water the pressure at the outflow end of the core was reduced. This phase of the displacement represented a depletion drive or blowdown of a reservoir. In most of the experiments a majority of the oil recovered by carbon dioxide after a water flood was recovered during this phase of the displacement. In this study a larger fraction of the oil was recovered by carbon dioxide in experiments in which the heavy East Texas crude oil was displaced than in the experiments in which the lighter West Texas crude oil was displaced. To aid in evaluation of the experiments, swelling, viscosity and solubility of COâ‚‚ in the crude oils were measured as a function of COâ‚‚ pressure.