Foamlike Dispersions for Mobility Control in CO2 Floods

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Abstract
At the reservoir temperature and pressure at which CO2 can displace a crude oil with high microscopic-displacement efficiency, its density and compressibility are close to those of the crude oil—and not greatly different from those of water itself. Because of this, the mechanical and chemical characteristics of a high-pressure, CO2-in-water "foam" cannot be assumed to be the same as those of an air/water foam at near-atmospheric pressure. This paper reports information on the mobility of foamlike dispersions in reservoir rock. The data come both from the recalculation of selected experimental work reported in the literature and from new experiments. An important criterion for these experiments is to eliminate or greatly reduce the influence of fluid compressibility, so as to approximate field conditions in CO2 floods more closely. The core flow experiments performed for this work meet this condition by use of the nonaqueous phase of either liquid CO2 at high pressure, or a light hydrocarbon to simulate dense CO2 in experiments performed at low pressure. We postulate that to be effective in retarding the growth of fingers or other instability patterns in CO2 floods while maintaining a high microscopic displacement efficiency, a foamlike dispersion of dense CO2 in surfactant/water should have the following characteristics. 1. Its aqueous-phase content should be as low as possible, to minimize oil trapping and to permit maximum contact between CO2 and the crude oil. 2. Its effective mobility in the reservoir rock should be adjustable, by some parameters accessible during its generation, to about that of the oil bank it is expected to form and to displace.