Three-dimensional Numerical Analysis of Fracture propagation in a Multilayered Reservoir for Enhanced Geothermal System

In Enhanced Geothermal System, characterization of Thermal/Hydrauric fracturing stimulation is important for optimizing the performance of geothermal reservoir. During geothermal process, thermal stress induced fracturing often caused secondary crack growth due to convective and conductive heat transfer from geothermal reservoir. However, the thermal induced process is not significant during the first stage of hydraulic fracturing, because the major fracture surface induced by hydraulic fracturing is generated rapidly, so the secondary thermal fracturing initiated from the major fracture surface. In this paper, sequential treatment process combining hydraulic and thermal fracturing stimulation is investigated using fully coupled poro-thermo-mechanical analysis and their influences on fracture propagation during reservoir stimulation are investigated using continuum damage mechanics with the embedded strong discontinuity approach. The numerical model of embedded strong discontinuity could provide explicit resolution of discontinuous behavior of fractures with strain localization scheme. The inelastic response of micro-crack growths of rock is described by the damage mechanics and the macroscopic fracture behaviors such as crack closure and opening effects are described by the embedded strong discontinuity approach. Also, statistical models of heterogeneity are used to account for a variety of rock fabric possibilities, because most rocks have strong internal heterogeneity, lateral variability and non-planar geometry. In many reservoir developments, multiply-fractured reservoirs are developed vertically or horizontally, so that estimation of crack paths in multi-layered reservoir formation is important to estimate the performance of reservoir. The role of coupled pore-thermal stresses induced by hydraulic pressure and convective and conductive heat source in the breakdown of rock in cold region is studied in multi-layered reservoir. The fracture propagation model in multi-layered reservoir will be combined with reservoir simulation in the future.