A laboratory-based approach to determine Archie's cementation factor for shale reservoirs

Abstract

Although production from shale gas reservoirs has been significantly improved in recent years, petrophysical characterization of these unconventional formations is still facing difficulties. Fluid saturation is one of the major petrophysical properties of gas shale reservoirs which has been the subject of many studies. Shale mineralogy, pore structure, water absorption, clay swelling and low permeability are perhaps the main reasons behind the failure of many methods proposed to determine water saturation under these circumstances. The aim of this paper is to show how the cementation factor of Archie's equation can be properly determine for a better estimation of fluid saturation in shale gas reservoirs. A series of tests were conducted on the samples taken from the Carynginia formation of North Perth Basin in Western Australia. The results obtained indicated that the average cementation factor of the samples is around 1.6 which can provide a good estimation of water saturation on the field scale. It appeared that the confining pressure may reduce the porosity of the samples and should be considered when the cementation factor is calculated. It was concluded that Archie's equation can still be a valuable asset for determination of fluid saturation in unconventional reservoirs if the cementation factor is accurately determined.