Measurement and revised interpretation of gas flow behavior in tight reservoir cores

Abstract

As more attention has been paid to low permeability hydrocarbon resources, a reliable and fast method to determine permeability of tight reservoir cores is required by both industry and research organizations. Gas flow in tight cores presents more complications under laboratory conditions due to gas slip phenomenon. For over half a century, the Klinkenberg correlation has been widely used in laboratories to obtain gas permeability in tight porous media through linear extrapolation of measured apparent permeabilities to infinite mean test pressure. This paper presents an experimental method to study the slip effects in gas permeability measurements for low permeability cores by applying a backpressure at the outlet of test sample. By increasing backpressure step by step, the gas slip effect is gradually reduced and finally becomes negligible when backpressure reaches or exceeds a critical value. This pressure is defined as minimum backpressure in this study. Therefore, the non-slip gas permeability can be determined without using Klingkenberg correlation with backpressures equal to or greater than minimum backpressure. Evident discrepancies were also found between the Klinkenberg permeability and non-slip permeability for very low-permeability cores. This study provided a straightforward method to experimentally determine permeability of tight reservoir cores by using gases. The developed technique can also be applied in the measurement of relative gas–liquid permeabilities in multiphase flow systems where difficulties were found when using Klinkenberg correlation.