Propagation of Elongated Fluid-Driven Fractures: Rock Toughness vs. Fluid Viscosity

Abstract

This paper studies the effect of the rock fracture toughness on the propagation of elongated fluid-driven fractures. We use the `tough PKN' model of Sarvaramini and Garagash (2015), an extension of the classical PKN model(Perkins and Kern, 1961; Nordgren, 1972), which allows for a non-zero energy release rate into the advancing fracture front(s). We provide a self-consistent analysis of a `tough' elongated fracture driven by arbitrary fluid injection law under the assumption of negligible fluid leak-off. We use scaling considerations to identify the non-dimensional parameters governing the propagation regimes and their succession in time, provide a number of analytical solutions in the limiting regimes for an arbitrary power-law injection, and also posit a simplified, equation-of-motion, approach to solve a general elongated fracture propagation problem during the injection and shut-in periods. Finally, we use the developed solutions for a tough elongated fracture to surmise the relative importance of the viscous and toughness-related dissipation on the fracture dynamics and broach the implications of the possible toughness scale-dependence.