Transient solution for a plane-strain fracture driven by a shear-thinning, power-law fluid

This paper analyses the problem of a fluid-driven fracture propagating in an impermeable, linear elastic rock with finite toughness. The fracture is driven by injection of an incompressible viscous fluid with power-law rheology. The relation between the fracture opening and the internal fluid pressure and the fracture propagation in mobile equilibrium are described by equations of linear elastic fracture mechanics (LEFM), and the flow of fluid inside the fracture is governed by the lubrication theory. It is shown that for shear-thinning fracturing fluids, the fracture propagation regime evolves in time from the toughness- to the viscosity-dominated regime. In the former, dissipation in the viscous fluid flow is negligible compared to the dissipation in extending the fracture in the rock, and in the later, the opposite holds. Corresponding self-similar asymptotic solutions are given by the zero-viscosity and zero-toughness (J. Numer. Anal. Meth. Geomech. 2002; 26:579-604) solutions, respectively. A transient solution in terms of the crack length, the fracture opening, and the net fluid pressure, which describes the fracture evolution from the early-time (toughness-dominated) to the large-time (viscosity-dominated) asymptote is presented and some of the implications for the practical range of parameters are discussed. Copyright (c) 2006 John Wiley & Sons, Ltd.