Boundary retention layer influence on permeability of tight reservoir

Abstract

The permeability of typical tight oil reservoir cores is measured using difference fluid medium (nitrogen, formation water, kerosene), and a capillary permeability model considering boundary retention layers is build. The computed values of the model are compared with experimental values of cores. The difference of permeability using different fluid medium is discussed concerning boundary retention layer thickness, movable fluid pore space and clay contents. The experiment results showed that targeted reservoir cores klinkenberg permeability K∞ was 66.86% of conventional gas permeability Kg, and water permeability KW was 11.66% of Kg, and oil permeability KO was 2.46% of Kg. KW and KO could characterize reservoir water injection and development difficulty better than Kg. Kh/K (ratio between permeability of capillary model considering and not considering boundary retention layer), is perfectly consistent with K∞/Kg, which indicates that capillary permeability model considering boundary retention layer has good consistency with seepage characteristics of actual reservoir. The tight cores have smaller effective pore-throat space for flowing, and get larger effect of boundary retention layers. The smaller the permeability core have, the closer between Kh/K and K∞/Kg. Boundary layer thickness are increased by Clay swelling, and flow channel are blocked by clay off and migration, that the main reason of KW smaller than K∞. The lower Kg cores have, the more KW/K∞ decrease magnitude. KO is much lower than K∞ and KW because of increased oil seepage resistance by two-phase seepage and boundary retention layer.