Saturation Distribution in a Linear System During Oil Displacement

Abstract

Abstract Displacement studies were performed on a Berea sandstone core in which a residual brine saturation 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 porous 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 displacement runs by calculations based on the continuity 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. Introduction A wide variety of experimental work on fluid displacement in porous media has appeared in the petroleum engineering literature during the last two decades. Along with this has appeared the theoretical treatment which forms the basis of our present concepts in this field. One of the first papers of background interest for this particular study was that of Leverett in which was developed the fractional-flow formula. A short time later Buckley and Leverett presented a form of the continuity equation as well as a method of using it and a simplified version of the fractional-flow formula (gravity and capillary-pressure terms neglected) to calculate the distance which any saturation has traveled in a given time interval. Terwilliger et al observed that after their water gas interfaced advanced a certain distance from the inlet of the system, all gas saturations over a certain interval beginning at the extreme flood front advanced at the same velocity. On the basis of the continuity equation they concluded that the change of fractional flow (gas) with saturation must be constant and this zone wherein all saturations moved at the same rate was named the "stabilized zone." They presented a method of calculating the saturation distribution in the stabilized and non-stabilized zones and obtained reasonable agreement between calculated and experimental values.