Abstract: In a WAG flood oil is displaced from a subterranean formation by injecting water alternately with gas into a single injection completion per pattern. The ratio of water to gas injected is the WAG ratio. In this invention, two separate injection completions are used in each pattern, with one placed directly above the other. A very low WAG ratio is used for injection into the bottom extremity of the formation. A very high WAG ratio is injected into the upper interval, at as high a rate as can safely be used without fracturing the formation. In the preferred embodiment, two horizontal well bores serve as the two completion intervals. Proper design of this method gives a vertical sweep efficiency of the gas that is several-fold greater than the best of previous WAG flood designs, especially in thin formations.

Abstract: A method for recovering oil from a subterranean formation by alternately injecting water and fluid miscible with the oil into the formation to displace the oil is disclosed. In this method, the wells are spaced sufficiently close together, and the water and miscible fluid are injected at a rate, such that a value between 0.3 and 1.5 is obtained for a dimensionless parameter. This parameter is a ratio of viscous flow forces to gravity forces. It is equal to the total injection rate of the water and miscible fluid divided by the product of the density difference between the miscible fluid and the water, the average vertical permeability of the reservoir, the area of the reservoir to be flooded by an injection well, and the sum of the mobilities of the miscible fluid and the water at steady state around the injection well.