Physics of Fluid-Rock Geomechanical Interactions: The Matrix//Fracture Interface

ABSTRACT: A fracture is a quasi-planar discontinuity that may develop a non-zero aperture and thus create a void space that is bounded by the faces of the adjacent blocks of matrix rock. Therefore, fracture aperture is governed by the movements of the bounding faces of the adjacent matrix blocks. Accordingly, it is necessary to understand the micro-physics of the matrix material, in terms of the process interactions between geomechanics and pressure which cause the bounding face of a matrix block to move. This knowledge comes from a micro-mechanics model that derives the emergent behaviours of a material point represented by a multi-connected solid framework (skeleton) and its contained pore system. The skeleton and pore system are taken as complementary space-filling networks that are each simplified into a rectified lattice. These geometric simplifications allow the geomechanical//pressure responses to be derived via analytical expressions. Application of this model to the fracture//matrix interface leads to the derivation of the sequence of local state changes (and possible far-field causes) required to transform a closed fracture to one with an open aperture. A plausible context for this set of process interactions is an ensemble of rock-mass blocks that are partitioned by an array of connected macro-scale fractures. That setting is characteristic of a fractured reservoir.