Hydromechanical Characterization of Shales on multiple Scales

Microstructural analyses by means of micro-scale imaging, laboratory tests of core samples, and formation hydraulic tests in boreholes are used to establish correlations between mineralogical, hydraulic and geomechanical properties of four investigated shale and claystone formations in Switzerland. The analyses spanning scales ranging from the micro- to the macro-scale indicate that the mechanical behaviour associated with clay content is a key factor determining on the one hand transport properties of the intact rock matrix and on the other hand the mechanism of self-sealing that controls the transport capacity of fractures in shales. Clay content from geophysical logs is additionally used to derive continuous profiles of transport properties such as porosity and permeability. The profiles are analysed statistically incorporating the borehole lithostratigraphic information to derive representative variogram descriptions of the formation facies, depicting structural bedding features of the stratigraphic and mineralogical profiles. The geostatistical descriptions are used to perform conditioned 3D simulations of porosity and permeability for the investigated formations. The described methodology thus establishes clay content as the leading property in order to characterize the transport mechanisms in each formation and accordingly derive quantitative models of transport property distributions.