DEM Study of Hydraulic Fracturing in Enhanced Geothermal Systems

Abstract

The paper presents results of a micro-mechanical DEM (discrete element modeling) study using the Particle Flow Code (PFC) of the hydraulic fracture initiation and propagation in enhanced geothermal systems (EGS). Hydraulic fracturing is the main means to stimulate and create flow paths to extract heat in hot dry rocks with insufficient permeability to inject and circulate fluids. Hydro-thermo-mechanical (HTM) coupled modeling is performed to analyze stress and strain changes around an injection wellbore to improve the understanding of the fracture initiation processes and the resulting fracture geometry. The study used a thermo-mechanically coupled Synthetic Rock Model (SRM) to preliminary validate previous research findings that were performed of the hydraulic fracturing in rocks but now taking into account the stresses induced by the temperature difference between fracturing fluid and the surrounding rock material. The study evaluated fracture geometry and orientation with respect to fracturing fluid temperature, viscosity, density, pressure, rock parameters and in-situ stress difference. The study used typical in-situ conditions including temperature and in situ stresses, and rock mechanical properties representative of crystalline rocks with low permeability.