If crossflow can occur between adjacent strata, sweep in the less permeable zones can be almost as great as that in the high permeability zones if the mobility ratio times the permeability differential is less than unity.
However, if no crossflow occurs between strata, sweep in the less permeable zone will be no better than approximately the square root of the reciprocal of the permeability differential.
At Daqing, a means was devised to improve this sweep problem when crossflow does not occur. Based on theoretical studies and practical results from Daqing pilot tests,separate layer injection was found to improve flow profiles, reservoir sweep efficiency, and injection rates, and can reduce the water cut in production wells. Numerical simulation studies reveal that the efficiency of polymer flooding depends importantly on the permeability differential between layers and when separate layer injection occurs.
