| Summary: | In this study, the effective stress law for the permeability of two core plugs selected from Berea (Cleveland Quarries, OH, USA) and Knorringfjellet (Longyearbyen, Svalbard, Norway) sandstones is studied experimentally by measuring the core permeability (k) under varying confining stress (σ c ) and pore pressures (P p ). The obtained results demonstrate that the permeabilities of the two core plugs decrease with increasing σ c or decreasing P p . The effective stress coefficient for the permeability (α k ) values are more than 1.0 for both sandstone core plugs indicating higher sensitivity of the permeability with respect to the applied P p compared to the applied σ c . The previously presented models for calculating α k , such as the Clay Free, Clay Shell, and Clay Particle models, are discussed and a new modified Clay Shell model considering spherical geometry is presented to account for the considerable contrast between the elastic moduli of quartz and clay minerals. The discussed models strongly depend on the magnitude of the considered elastic moduli for the clay minerals. While the Clay Shell and Clay Particle models are capable of describing the observed α k values by considering extremely low elastic moduli for clays, the new modified Clay Shell model is capable of predicting α k values by considering moderate to low values of elastic moduli of clays. The increasing trend of α k values by increasing the σ c is discussed and a new correlation based on the observed k values for calculation of α k is presented. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.
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