Abstract: A process is provided for selectively placing a permeability-reducing material in an interval of a subterranean hydrocarbon-bearing formation penetrated by a well bore to inhibit the vertical flow of fluid between the well bore and an aquifer underlying the interval. The process is performed by simultaneously injecting a pair of fluids into the well bore, wherein one fluid has a density substantially less than the density of the other, and displacing the fluids out into the interval. The two fluids directly contact one another as they are displaced, however, the density difference between the fluids causes the first fluid to preferentially enter an upper portion of the interval and the second fluid to preferentially enter a lower portion of the interval under the force of gravity stratification or gravity segregation.

Abstract: Two fluids having different mobilities are sequentially injected in repeating cycles into a naturally-fractured subterranean oil-bearing formation to facilitate oil recovery therefrom. The first fluid is a mobility adjusted fluid containing a mobility control agent which imparts reduced mobility to the fluid. The mobility adjusted fluid displaces oil from the formation fractures to a production well. The second fluid has a higher mobility than the first fluid which enables it to displace oil from the formation matrix to the formation fractures. The cycle is repeated to produce the newly displaced oil in the fractures.