There are known recovery processes for oil from oil reservoirs by a miscible displacement process, which include the injection, at least in one well of an oil reservoir, of a quantity of a miscible displacement agent, consisting of carbon dioxide, equal to about 20% of the saturated-pore volume of hydrocarbon. Next an air slug can be injected, this air slug replacing the displacement agent left in the oil reservoir by residual saturation of the water flood area. Then continuous injection of water is undertaken, the oil reservoir fluid being withdrawn through other wells.
The disadvantage of these processes is that it is necessary to use rather large amounts of the displacement agent of which about 90% remains in the oil reservoir. In the case of an oil reservoir having a certain heterogenous degree of air blended with the oil, the displacement agent suffers a miscibility loss across a certain section of the displacement front.