What Could We See at the Production Well Before the Thermal Breakthrough?

Abstract

In the EGS Collab project, hydraulic fracturing is being studied through laboratory tests, field experiments, and mathematical modeling, in order to improve understanding of fluid and heat flow in Enhanced Geothermal Systems (EGS). The first field experiment is designed to create possibly penny-shaped fractures that connect parallel injection and production wells, and a subsequent thermal injection test is planned to help characterize fracture parameters. We performed thermal-hydrologic simulations of the planned thermal test to estimate the minimum injected flow rate necessary for obtaining a temperature signal at the production well within a reasonable time period. Using the largest injection rate based on our pumping capacity, the simulation results indicate that the injected thermal signal will not reach the production well within 15 days, which may be the maximum time considered feasible for thermal test duration. However, small thermal perturbations at the production well could be observed within this time frame, due to both thermodynamic effects and the non-uniform initial temperature distribution in the fracture. These perturbations are more sensitive to flow parameters than thermal parameters, but could be useful for fracture characterization, provided field temperature measurements are sensitive enough.