4 - Fluid Flow and Coupled Hydro-Mechanical Behavior of Rock Fractures

Abstract

Publisher Summary This chapter presents the continuity equation (derived using the mass conservation law) and equations of motion (derived using the momentum conservation law). The most commonly applied conceptual model for flow through a single fracture is derived from a much simplified Navier–Stokes equation of viscous fluid flow through a pair of smooth parallel surfaces of narrow width often called the ‘parallel plate model’ or the Cubic Law in rock mechanics literature. The flow analysis of a fracture network is based on the elements of fracture segments, intersections, and cycles. The chapter describes the technique for modeling the fluid flow and deformation of rock fractures that assumes that rock blocks are impermeable, so that there is no fluid interaction between the fracture and its parent rock matrix. The fluid flow and block motion/fracture deformation are coupled through a two way interaction: (1) change of fluid pressures on the boundary surfaces of blocks affects the motion and deformation of blocks and, in turn, the deformation of fractures; and (2) the change of hydraulic apertures of fractures affects its transmissivity, flow rate, and fluid pressure distribution along the fracture surfaces. The effect of fluid pressure on the deformation and change of hydraulic aperture of fractures is represented by a similar ‘effective stress' concept and calculated through the constitutive laws of the fractures or point contacts in discrete element methods.