The EGS Collab Project: Stimulating and Simulating Experiments in Crystalline Rock in An Underground Research Site

The primary objective of the EGS Collab Project sponsored by DOE is to increase the understanding needed to efficiently implement enhanced geothermal systems (EGS). The EGS Collab project is a collaborative research environment studying stimulation of crystalline rock at the 10 meter scale. High-quality characterization and monitoring data are collected during stimulation and flow tests to allow comparison to numerical coupled process models in an effort to build confidence in the codes and improve modeling techniques. The Experiment 1 test bed, located at the Sanford Underground Research Facility (SURF) in Lead, SD at a depth of approximately 1.5 km is being used to examine hydraulic fracturing. The testbed was characterized using numerous field-based geophysical and geologic techniques and laboratory testing, and a well-instrumented test bed was created to allow us to carefully monitor fracture stimulation events and flow tests. A number of hydraulic stimulation tests at several locations in one well have been performed, creating new fractures that connect to existing fractures between the injection and production boreholes. Long-term ambient and chilled water injection tests have been performed as an analog to EGS, and system changes resulting from these water injections have been monitored using geophysical monitoring, flow, temperature, and pressure measurements, tracer tests, and microbiology. Here, we summarize the tests performed, issues identified including poroelastic and thermoelastic effects, Joule-Thomson effects, restarting effects, indications of flow channeling, and the scientific findings to date from Experiment 1. We are currently investigating and designing a second test bed aimed at investigating shear stimulation (Experiment 2).