Lawrence Berkeley National Laboratory

This document provides a distillation of learnings of the EGS Collab (Collab) project for several topics of interest requested by the Utah Frontier Observatory for Research in Geothermal Energy (FORGE) project. This document was written following the completion of Collab Experiment 1, but prior to beginning Collab Experiment 2. Recommendations offered herein are perspectives offered by Collab scientists in support of FORGE. The United States has an enormous indigenous renewable energy potential from enhanced geothermal systems (EGS). To realize this potential, the US Department of Energy (DOE) Geothermal Technologies Office (GTO) has made significant investments into research to eliminate impediments to developing EGS. Two major current projects are Collab initiated in 2017, and the FORGE project initiated with a site selection process in 2015. Collab is a collaborative multi-national-lab, university, and commercial entity research endeavor bringing together a team of skilled and experienced subsurface process modeling, monitoring, and experimentation researchers and engineers to focus on intermediate-scale EGS reservoir creation processes and related model validation in crystalline rock. Collab is utilizing readily accessible underground facilities to refine the understanding of rock mass response to stimulation using experiments on the order of 10 m scale under EGS-relevant stress conditions. Experimental results from Collab stimulation, flow, tracer, and thermal tests are being used to validate coupled thermal-hydrological-mechanical-chemical (THMC) modeling approaches applicable to EGS. Collab is also testing and improving conventional and novel field monitoring tools. The project focuses on understanding and predicting permeability enhancement and evolution in crystalline rock. This focused research includes creating sustained and distributed permeability for heat extraction by generating new fractures that complement existing natural fractures. FORGE has the mission of establishing an EGS field test site that enables cutting-edge research and testing for EGS technology to identify a replicable, commercial pathway to EGS. The FORGE team is developing the EGS field test site near Milford, Utah. The two projects differ in some attributes, including spatial scale (Collab / FORGE - 10-m / reservoir), access to the rock (short boreholes and nearby instruments / deep wells and standard field geophysical equipment), environmental conditions (cool rock at reasonable stress / hot rock at reasonable stress), focus (direct investigation / development of a testbed and management of a research program), and project structure (integrated team / science and engineering framework supporting many individual research teams). The specific topics of this report requested by FORGE are: 1) data processing, annotation, and integration; 2) processing seismic data, 3) connecting geophysics, fractures, and flow systems, and 4) challenges of modeling fractured flow systems. Each of these topics is briefly discussed in this executive summary and covered in substantially greater detail in the main document. Numerous conference and journal papers are cited in the report that provide additional information. Many lessons have been learned. Some are not directly transferable to FORGE, but the underpinnings of the lessons may be applicable.