Recent Advances in Global Fracture Mechanics of Growth of Large Hydraulic Crack Systems in Gas or Oil Shale: A Review

This chapter reviews the recent progress toward computer simulation of the growth of vast systems of branched hydraulic cracks needed for the efficient extraction of gas or oil from shale strata. It is emphasized that, to achieve significant gas extraction, the spacing of parallel hydraulic cracks must be on the order of 0.1m, which means that the fracturing of the entire fracking stage would require creating about a million vertical cracks. Another emphasized feature is that the viscous flow of fracking water along the hydraulic cracks must be combined with Darcy diffusion of a large amount of water into the pores and flaws in shale. The fracture mechanics on the global scale is handled by the crack band model with gradual postpeak softening and a localization limiter in the form of a material characteristic length. Small scale computer simulations demonstrate that the computational approach produces realistically looking results.