Experimental study of fluid transport processes in the matrix system of the European organic-rich shales: II. Posidonia Shale (Lower Toarcian, northern Germany)

Abstract A laboratory study has been conducted to investigate the transport of gases (He, Ar, CH 4 ) and water in the matrix of Lower Toarcian Posidonia Shale samples from three shallow boreholes in northern Germany. The maturity of the organic matter of the shale samples ranged between 0.53 and 1.45% vitrinite reflectance (VR r ). The measurements were performed at effective stresses ranging between 6 and 37 MPa and a temperature of 45 °C. The effects of different controlling factors including permeating fluid, maturity, anisotropy, moisture content and effective stress on the fluid conductivity were analyzed and discussed. Permeability coefficients measured perpendicular and parallel to bedding (3 · 10 − 22 to 9.7 · 10 − 17  m 2 ) were within the range previously reported for other shales and mudstones. They exhibited a strong dependence on permeating fluid, maturity, anisotropy, moisture content and effective stress. The permeability coefficients measured with helium as permeate were consistently higher (up to two times) than those measured with argon and methane. Permeability coefficients measured with water were up to three orders of magnitude lower than Klinkenberg-corrected gas permeability coefficients measured with helium and methane under similar experimental conditions. Among the samples studied, the lowest porosity and permeability coefficients were measured on samples of intermediate thermal maturity (0.88% VR r , oil-window). Permeability coefficients (He, CH 4 ) measured parallel to bedding were up to more than one order of magnitude higher than those measured perpendicular to bedding. Permeability coefficients measured with He and CH 4 on a dry sample were up to two times higher than those measured on a sample with the “as-received” moisture content. All samples showed a nonlinear reduction in permeability parallel to bedding with increasing effective stress (6–37 MPa). The permeability anisotropy and stress dependence of permeability were controlled by the mineralogy.