Numerical Simulation of Hydraulic Fracturing in Tight Gas Shale Reservoirs

Hydraulic fracturing of tight gas shales is a relatively new method of producing economically from extremely low permeability reservoirs. Due to the low permeability, it is crucial that fracturing treatments are able to efficiently create regions of enhanced permeability in the reservoir. The mechanical properties of prospective shale mean that stress interactions between adjacent fractures can be of real consequence to the efficiency of the treatment, and alternative treatments to mitigate these effects have been designed. The aim of this research is to conduct numerical simulation of alternative treatment designs, and objectively evaluate critical parameters. In particular, key aspects of the socalled Texas Two Step method are simulated. This treatment aims to create zones of altered stress anisotropy between pressurised fractures. This study examines the behaviour of said zones as the distance between the fractures is altered, in parallel with literature describing the method. Explanations for unusual fracture curvature behaviour are provided. Further studies examine fracture reorientation within a modified stress field such as that created by the treatment. Rates of reorientation are measured under varying levels of stress anisotropy, initial fracture length and orientation to the stress field. The influence of pre existing natural fractures on the path of a hydraulic fracture is investigated through further simulations. The effects of natural fracture permeability and interface properties are studied. The impact of shear stress caused by a propagating fracture is also examined, and the possible implications for interpretation of microseismic data discussed. Finally, a new treatment for simultaneous fracturing with reduced stress shadowing is proposed and simulated.