Method for recovery of oil from reservoirs of non-uniform permeability

摘要

In an oil bearing formation including at least two strata of differing permeabilities oil recovery is enhanced by the controlled injection of a miscible fluid under conditions selected so that the fluid has a density substantially greater than or substantially less than the density which has been determined for the oil in the reservoir in order to encourage gravity segragation of the drive fluid and oil. For example, where it is determined that stratum of lesser permeability is verticially below stratum of greater permeability, a drive fluid having a density substantially greater than the density of the oil results in the gravity segregation of the drive fluid into the lower, less permeable, layer, thereby providing for a subtantially equal drive rate between the more permeable and less permeable layers. In the situation in which it is determined that the less permeable layer is vertically above the more permeable layer the drive fluid is selected to be substantially less dense than the oil in the reservoir, again resulting in the gravity segregation of the drive fluid into the less permeable layer and resulting in the oil being driven through both strata at substantially the same rate. In situations in which the strata are of variably different permeabilities, the cyclic application of drive fluids of substantially greater and substantially lesser densities than the oil in the reservoir results in an efficient sweeping of the oil from all strata in the reservoir. In each of these processes, the pressure of the reservoir is maintained, relative to the temperature and other conditions of the reservoir, so that the drive fluid has the required density.