Abstract
Three components are typically needed to extract geothermal energy from the subsurface: 1. hot rock, 2. a heat transfer fluid, and 3. flow pathways contacting the fluid and the rock. These naturally occur in many locations resulting in hydrothermal systems, however there are enormous regions containing hot rock that do not naturally have adequate fluid, and/or appropriate fluid permeability to allow hot fluid extraction. Some type of engineering or enhancement of these systems would be required to extract the energy. These enormous regions provide the possibility of long-term extraction of significant quantities of energy. Enhanced (or engineered) Geothermal Systems (EGS) are engineered reservoirs created to extract economical amounts of heat from low permeability and/or porosity geothermal resources. There are technological challenges that must be addressed in order to extract the heat. These include proper stimulation, effective monitoring, reservoir control, and reservoir sustainability. The US DOE Geothermal Technologies Office and geothermal agencies from other countries have supported field tests over a range of scales and conditions. A current US field project, the EGS Collab Project, is working nearly a mile deep in crystalline rock at the Sanford Underground Research Facility (SURF) to study rock stimulation under EGS stress conditions. We are creating intermediate-scale (tens of meters) test beds via hydraulic stimulation and are circulating chilled water to model the injection of cooler water into a hot rock which would occur in an EGS, gathering high resolution data to constrain and validate thermal-hydrological-mechanical-chemical (THMC) modeling approaches. These validated approaches would then be used in the DOE’s flagship EGS field laboratory, Frontier Observatory for Research in Geothermal Energy (FORGE) underway in Milford, Utah and in commercial EGS. In the EGS Collab project, numerous stimulations have been performed, characterized, and simulated and long-term flow tests have been completed.
Highlights
Three components are typically needed to extract geothermal energy from the subsurface: 1. hot rock, 2. a heat transfer fluid – typically water or brine, carbon dioxide has been considered, and 3. flow pathways that provide proper heat transfer contact between the fluid and the rock. These combined components occur naturally in many locations resulting in hydrothermal systems, there are enormous regions containing hot rock that do not have adequate fluid, and/or appropriate fluid permeability
There are technological challenges, where improvements are needed. These include: (1) effective stimulation techniques to suitably create subsurface “heat exchangers” that communicate between multiple wells by fractures in different rock types and under different stress conditions, (2) techniques to image/monitor permeability enhancement and evolution at the reservoir scale at the resolution of individual fractures, (3) additional technologies for zonal isolation for multistage stimulations under elevated temperatures, (4) technologies to isolate zones for controlling fast flow paths that result in early thermal breakthrough, and (5) scientifically-based long-term EGS reservoir sustainability and management techniques [3]
The goals of the FORGE project are to (1) provide an underground laboratory for developing and testing innovative tools and stimulation techniques for developing EGS reservoirs, (2) extend existing technologies developed for oil and gas beyond current capabilities to successfully produce electricity from hot crystalline rocks, (3) demonstrate technologies that can be applied across the US, (4) provide domestic and international scientists and students with funds for research to expand future energy security and availability, and (5) demonstrate suitability and safety of large-scale geothermal energy development to the public
Summary
Three components are typically needed to extract geothermal energy from the subsurface: 1. hot rock, 2. a heat transfer fluid – typically water or brine, carbon dioxide has been considered, and 3. flow pathways that provide proper heat transfer contact between the fluid and the rock. The goals of the FORGE project are to (1) provide an underground laboratory for developing and testing innovative tools and stimulation techniques for developing EGS reservoirs, (2) extend existing technologies developed for oil and gas beyond current capabilities to successfully produce electricity from hot crystalline rocks, (3) demonstrate technologies that can be applied across the US, (4) provide domestic and international scientists and students with funds for research to expand future energy security and availability, and (5) demonstrate suitability and safety of large-scale geothermal energy development to the public. Investigations to improve drilling, stimulation, injectionproduction, and subsurface geophysical imaging technologies will be performed These will help establish and sustain continuous fluid flow and energy transfer from an EGS reservoir
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