ICE 2022


The Utah Frontier Observatory for Research in Geothermal Energy (FORGE) is a full-scale field laboratory in south-central Utah, USA. The FORGE project is dedicated to advancing technologies, driving innovation, and growing expertise in Enhanced Geothermal System (EGS) development. The project is funded by the U.S. Department of Energy and managed by the Energy & Geoscience Institute at the University of Utah. The project aims to demonstrate EGS technologies that can be applied across the U.S.A. and globally, in hot, abrasive, low permeability rocks. Critical to the success of developing large-scale, economically sustainable EGS reservoirs is the ability to characterize, initiate and sustain the interconnected fracture networks required to extract heat in crystalline basement rocks over periods of 10s of years with small temperature declines. The granitic and metamorphic basement rocks at the Utah FORGE site have bottom hole temperatures close to 230 deg C, which pushes the limits of conventional wireline logging, drilling, and isolation tools. The application of through-the-bit conveyed logging technologies at Utah FORGE has proved effective at mitigating the downhole temperature challenge and provided for the logging of highly deviated injection wells. The integrated advanced analysis of resistivity and ultrasonic borehole image and dipole sonic data, including 3D far-field acoustic analysis, has provided a detailed subsurface characterization of fracture type, fracture intensity, fracture geometries and fracture apertures. These data have also provided the Utah FORGE team an enhanced understanding of the local stress regime and structural history, through borehole stress observations and fracture cross-cutting relationships. Ultimately, these fracture characterization data have been used to development a representative discrete fracture network (DFN) model, required for predicting the characteristics of the stimulated EGS reservoir. Simulations of the hydraulic stimulation of an injection well have predicted that existing natural fractures, represented by the DFN, could control the efficacy of the treatment and create a large volume of connected flow pathways in the stimulated region. This case study shows how existing technologies and expertise, developed from unconventional hydrocarbon reservoir characterization, are being leveraged to support subsurface fracture characterization and modeling in this pioneering geothermal project.