Grain and pore microtexture in sandstone sill and depositional sandstone reservoirs: preliminary insights

Petrographical microtextural analysis and conventional core-plug analysis of samples from a depositional sandstone and a sandstone sill are used to compare with similar data derived from micro-CT (MCT) analysis of the same samples. A remarkable richness of information derived from the MCT data identifies isotropic granular and pore fabrics at the micrometre-scale in the sandstone sill that contrast markedly with the laminated fabric in the depositional sandstone. In the sandstone sill, porosity and permeability are more homogenous than in the depositional sandstone, in which lamination creates approaching two-orders of magnitude difference in permeability and enhances horizontal permeability relative to vertical permeability. In the sill, lower pore- and throat-shape factors and larger pore coordinate numbers are present than in the depositional sandstone. Preservation of the isotropic pore and grain structure in the sandstone sill is indicative of significant fluidized flow normal to the fracture margin during emplacement.