Simulations of the 3D Geothermal Heat Flow in Fractured Media

Abstract

Understanding heat exchange from injected fluid in subsurface fractured media is crucial for successful operation of enhanced geothermal systems (EGS). To complement our understanding of the EGS-Collab Experiment 1 site, we performed geothermal numerical simulations by modeling heat flow and tracer transport through three-dimensional fractured media. Different conceptual models of fracture geometry setups were used for the heat-flow-transport numerical simulations. Prior to flow simulations: (i) we mapped fractures geometry into continuum computational mesh; (ii) rescaled aperture and permeability of fractures and rock matrix; (iii) projected injection, production and monitoring wells into the simulation domain according to their known locations. To account for coupled matrix and fracture heat-flow-transport, we employed novel modeling approach by translating the fracture systems to subsurface flow and reactive transport model. We used dfnWorks software to generate fracture networks and PFLOTRAN to simulate heat-flow-transport dynamics. The cold liquid water injection was simulated by using temperatures time-series at the injection source according to hourly averaged temperature data used at injection well at the Experiment 1 site. In addition, we included temperature gradient between injection and production wells to illustrate its effect on simulated temperatures at the producing wells. Our simulations showed that tracer behavior depends on fracture geometry setup. Thermal simulations using three different fracture configurations showed that faster heat response between injection and production wells can be achieved when there is a direct channel linking these two wells.