Experimental study of fluid transport processes in the matrix system of the European organic-rich shales: I. Scandinavian Alum Shale

This contribution presents results from a laboratory study investigating the fluid (gas/water) transport properties in the matrix system of the Scandinavian Alum Shale. The maturity of the organic matter of the shale samples ranged between 0.5 and 2.4% vitrinite reflectance (VRr). Gas (He, Ar, CH4) and water flow properties were determined at effective stresses ranging between 5 and 30 MPa and a temperature of 45 degrees C. The effects of different controlling factors/parameters on the fluid conductivity including permeating fluid, moisture content, anisotropy, heterogeneity, effective stress, pore pressure, and load cycling were analyzed and discussed. Pore volume measurements by helium expansion were conducted under controlled in situ effective stress conditions on a limited number of plugs drilled parallel and perpendicular to bedding. For Alum Shale the intrinsic permeability coefficients measured parallel and perpendicular to bedding (6.10(-22)-8.10(-18) m(2)) were within the range previously reported for other shales and mudstones. Permeability coefficients were strongly dependent on permeating fluid, moisture content, anisotropy, effective stress and other sample-to-sample variations. The intrinsic/absolute permeabilities measured with helium were consistently, higher (up to five times) than those measured with argon and methane. Permeability coefficients (He, CH4) measured on a dry sample were up to six times higher than those measured on an as-received sample, depending on effective stress. The effect of moisture on measured permeability coefficients became more significant as effective stress increased. Permeability coefficients (He, CH4) measured parallel to bedding were up to more than one order of magnitude higher than those measured perpendicular to bedding. Parallel to bedding, all samples showed a nonlinear reduction in permeability with increasing effective stress (5-30 MPa). The stress dependence of permeability could be well described by an exponential relationship. (C) 2013 Elsevier Ltd. All rights reserved.