P. T. BAIL J. E. BOBEK* MEMBERS A/METhis paper presents the results of model studies made to demonstrate the validity of applying the "basic" waterflooding scaling relationships of Rapoport! to water-wet reservoirs composed of communicating strata of different permeability. Results demonstrate that these relationships can be validly applied, and also show the combined effect of variables on recovery. This demonstration was needed to confirm that the sizable effects of communicating strata on waterflood behavior, observed in model studies, were actually representative of field behavior.

In reservoirs containing soft shales interbedded with oil-producing sands, it is possible to have water movement from the shales into the sands during reservoir depletion. This paper presents the results of scaled flow-model tests performed to investigate the efficiency of oil displacement by this vertical influx of water into oil-producing sands. In these model tests, the effects of rate of influx and rock wettability were considered.Oil recoveries by shale-water influx and by water flooding were compared after 0.4 hydrocarbon volume of water entered the producing sand. This comparison was made for water-wet and oil-wet systems. In water-wet sand, shale-water influx produces slightly less oil than conventional water flooding; in oil-wet sand, shale-water influx produces about one-half as much oil as conventional water flooding. In another type of comparison, it was found that shale-water influx followed by water flooding recovers less oil than water flooding alone. This is true for both water-wet and oil-wet sands. A comparison of tests run at different rates of shale-water influx shows that oil recovery is insensitive to rate in water-wet sand; in oil-wet sand, oil recovery decreases with decreasing rate of influx.

Displacement studies were performed on a Berea sandstone core in which a residual brine sat uration was initially present. The oil saturation was determined as a function of time and distance by measuring the electrical resistance of segments of the core. Relative permeability was measured by a modified Penn State method for the same porouE medium used in the displacement stUdies and static capillary pressures were determined for adjacent samples. The shape of the stabilized zone and recovery at water breakthrough were calculated using both measured and computed relative permeability data and these agreed with the experimental~ The fraction of brine flowing at a given oil saturation was determined from saturation distribution data at various times and distances during the dis placement runs by calculations based on the contin uity' equation. As the stabilized zone is formed, the shape of the fw vs So curve approaches a straight line for a certain range of saturations.