Textural Characteristics of Shale Deformations, and Associated Distribution Models: Implications for Shale Reservoir Fluid Flow

摘要

We describe a new (or under-reported) type of deformation feature that has some of the textural characteristics of both a fracture and a shear band. The examples described occur in experimentallydeformed source-rock materials, and in tight limestones, both of which are constituents of many shale reservoirs. The deformation features, which emerge at very low magnitudes of bulk strain, create new dilative zones within the rock, and thus enhance the flow characteristics. Direct observation of fluid flow, involving neutron-tomography experiments of these experimental samples, reveals flow behaviours that lead to the inference that the features have an unusual set of properties: both high capillary pressure and high permeability. Detailed textural observations generate insights that lead to hypothesized physical explanations for the surprising flow characteristics. Our present understanding is that these features can form in the low-strain (and low energy-cost) conditions that can be achieved in hydraulic stimulation operations. If such deformations do occur in the suitable rock types within shale sequences, their role in fluid flow may be significant but heretofore unrecognized.