Areal Sweep Efficiency Increases By Scheduled Changes Of Injection-Producing Patterns

Abstract

Abstract Results and procedures are presented which demonstrate a novel means Of changing the injection and producing pattern (rotation) to increase substantially the areal sweep efficiency and recovery during pattern water flooding. Two types of laboratory tests were made. One series was made On sand-packed areal models utilizing oil and water solutions with an oil-water viscosity ratio of approximately 1. A second series of tests was made on Hele-Shaw (fluid mapper) models utilizing glycerol solutions to represent both oil and water with mobility ratios of 1, 3.5 and 9.2. Based on the sand-packed model studies, it is concluded that by injecting into the center well a volume of water equal to approximately 50% of the volume normally required for breakthrough, then rotating the injection into a diagonal opposite well, the areal sweep efficiency at breakthrough and at a water-oil ratio of 90:1 is increased 5–8% as compared to conventional five-spot flooding. This would mean an increase in oil recovery of about 6–9%. From the fluid mapper studies it is concluded that:at a mobility ratio of 1, the areal sweep efficiency is increased by approximately 10% by a scheduled rotation that does not entail shutting in the center well, but maintains a given injection ratio (1:5.9) between the center and offset diagonal wells,at a mobility ratio of 1, the areal sweep efficiency of an inverted nine-spot rotated to a five-spot is also increased by approximately 10%;the areal sweep efficiency at adverse mobility ratio is reduced due to viscous fingering. However, an increase in sweep efficiency over conventional five-spot flooding continues to be observed on the rotated tests.