Analytical and Numerical Modeling of Heat Transport in Fractured Reservoirs

Abstract

Modeling of thermal perturbations induced by injecting fluids of different temperature into deep fractured reservoirs is important for design and analysis of geothermal energy production including enhanced geothermal systems, and thermal energy storage. A novel analytical solution was first developed to couple global heat convection-conduction in fractures with heat conduction in the rock matrix and aquitards. This coupling was developed by using the unified-form diffusive flux equations recently developed for various shapes of matrix blocks and aquitards (Zhou et al., 2017a, b). A number of generic scenarios of flow regimes and system types were considered for a general study. We then used TOUGH2-MP/EOS1 to model the cold-water injection test planned for the sub-vertical hydraulic fracture at the EGS Collab test site. Our modeling results of water injection and heat transfer in the planned fracture of dimension 12 m × 10 m suggest that a measurable thermal breakthrough may not occur at the production well within the test period of 100 days. This infeasibility may be attributed to (1) small fracture aperture (i.e., 100 μm) and (2) high heat gain from the rock matrix with a large thermal diffusivity