The advent of shale production has transformed the energy industry, however to date a generic understanding of pore structures within these unconventional systems has been lacking, which, in turn, has limited and understanding of recovery mechanisms within these reservoirs, leaving total reservoir recovery extremely low. In this study we compare and contrast two qualitatively different pore systems. Organic hosted porosity (existing on the nanometer scale and common in unconventional shale reservoirs) was imaged using 3D FIB-SEM techniques, and intergranular porosity (common in conventional sandstone reservoirs and existing on the micrometer scale) was imaged using micro-CT techniques. Scale independent connectivity metrics found the intergranular pore network to be much better connected than the organic hosted pore network, despite similar total porosity. This contrast is explained by strong variations in pore shape (as measured by sphericity and pore network curvature) which are in turn explained by variations in the geological processes responsible for the genesis of the pore network. The impact of such changes in pore shape on pore network connectivity was examined by creating a suite synthetic pore geometries using both erosion / dilation of the existing network and image guided object based methods, showing strong statistical agreement between the imaged and synthetic pore networks. These synthetic pore networks were then used to examine how connectivity changes as a function of porosity (as may arise by varying degrees of shale maturity, or by reservoir diagenesis), showing that network connectivity, needed for effective capillary imbibition, is much easier to achieve in organic-type pore networks than in the intergranular-type pore networks. We then review how such techniques might be applied to solve problems within the petroleum industry, including the development of new pore-scale core analysis techniques to access fundamental petrophysical parameters and the application of wellsite imaging to aid completion spacing and geosteering.

The advent of shale production has transformed the energy industry, however to date a generic pore scale recovery mechanisms (governed by pore network structure) has been lacking. Two qualitatively different pore systems were compared and contrasted using scale independent techniques, finding organic hosted porosity (nanometer scale and common in unconventional reservoirs) to be much better connected than intergranular porosity (micrometer scale and common in conventional reservoirs). This contrast is explained by variations in pore shape, caused in turn by variations in the geological processes responsible for pore network genesis. These processes were examined by creating a suite synthetic pore geometries with strong statistical agreement between imaged and synthetic pore networks. Synthetic pore networks were then used to examine how connectivity changes with porosity (as may arise by varying degrees of shale maturity, or by reservoir diagenesis), showing that network connectivity, needed for effective capillary imbibition, is much easier to achieve in organic-type pore networks than in the intergranular-type pore networks. We then review how such techniques might be applied to solve problems within the petroleum industry, including the development of new pore-scale core analysis techniques and the application of wellsite imaging to aid production operations.