A Computational Investigation of Seismic Wave Focusing as a Means to Fracture Shale Reservoir

Hydraulic fracturing can only generate fractures within the vicinity of the wellbore. Moreover, natural and hydraulic fractures are difficult to characterize, and the water disposal process is linked to environmental concerns including induced seismicity. Recent laboratory efforts report on the application of shock-wave comminution to micro-fracture considerable target bulk volumes of various porous materials such as limestone and concrete. The physical process is similar to lithotripsy; a widely applied kidney-stone medical treatment procedure. Few studies of rock comminution have been conducted at reservoir conditions. This work: 1) develops a coupled seismic-flow simulation model that can predict the initiation of comminution at reservoir conditions and 2) applies the simulators in numerical experiments to investigate the potential for seismic fracturing.;A high-resolution, coupled single phase flow and transient geomechanics model for shale comminution is developed. In this model, the matrix rock is treated as a continuous porous medium and Biot's theory is applied to describe the bulk momentum balance. Wells are represented as internal boundaries within the mesh. Periodic or aperiodic deformations may be applied in addition to fluid injection and production. Two fully-implicit, fully-coupled, two-dimensional simulators are developed. One uses a finite difference method to approximate all equations, while the other uses finite volume methods. Mohr-Coulomb failure criterion and strain energy release rates are computed, and are used to judge the crack initiation and comminution processes.;The simulators are validated numerically for accuracy and correctness, and are compared to analytical solutions for simple cases. An investigation is conducted to evaluate the energy attenuation that occurs during seismic wave propagation. By controlling the generated seismic waves, comminution can be achieved in our model and they can be controlled to initiate at intentional target locations away from seismic sources.;Compared to hydraulic fracturing that can only stimulate volumes near the well, seismic waves can generate fractured volumes at target locations away from the wells. These preliminary results are encouraging, and provide guidance to the development of next steps in the laboratory.;A computational assessment shows that seismically induced comminution maybe realizable at reservoir conditions. Seismic wave comminution may become a novel technology that will complement hydraulic fracturing to increase recovery efficiency from unconventional reservoirs.