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DOE OSTI2025

Grid Value Analysis of Geothermal Systems for End-Use Applications

Fuel based end-uses for residential, commercial, and industrial consumers require a technology change to achieve economy-wide decarbonization. Space heating accounts for 42% of residential and 32% of commercial energy demand, much of which is currently met through carbon emitting fuels. Industrial energy use is heavily fuel based with electricity currently representing 13% of energy demand. Geothermal heat pumps (GHPs) and geothermal direct use can eliminate the need for CO2 emitting and simultaneously allow for more efficient electrification of end uses. Past work has assessed the impact on total energy costs and generation investments but did not identify specific grid services benefited. Energy usage in residential and commercial structures was assessed by leveraging data from ComStock and ResStock models. These models utilize housing attributes, occupancy patterns, weather data, and sophisticated energy simulations to generate hourly load profiles for individual buildings identified by unique IDs associated with their locations. Industrial sector energy use was evaluated using information from the Manufacturing Energy Consumption Survey (MECS) as well as plant utilization data from the US Census to estimate hourly plant operations. The change in end-use demand for electricity, natural gas, and other fuels was calculated for different technologies that could meet this need. Using the ReEDS capacity expansion model, we produce regional price profiles that capture the grid benefit associated with the amount and timing of energy shifts in the power system from the adoption of geothermal systems relative to other technologies that could meet space heating, space cooling, and process heat requirements. We find that geothermal systems for meeting end-use demand add value to the energy system. In buildings where geothermal systems increase grid costs, these values are offset by reduced fuel costs and benefits to externalities, including emissions and health impacts.

decarbonization↗

DOE OSTI2014

Tracer Methods for Characterizing Fracture Creation in Engineered Geothermal Systems

The aim of this proposal is to develop, through novel high-temperature-tracing approaches, three technologies for characterizing fracture creation within Engineered Geothermal Systems (EGS). The objective of a first task is to identify, develop and demonstrate adsorbing tracers for characterizing interwell reservoir-rock surface areas and fracture spacing. The objective of a second task is to develop and demonstrate a methodology for measuring fracture surface areas adjacent to single wells. The objective of a third task is to design, fabricate and test an instrument that makes use of tracers for measuring fluid flow between newly created fractures and wellbores. In one method of deployment, it will be used to identify qualitatively which fractures were activated during a hydraulic stimulation experiment. In a second method of deployment, it will serve to measure quantitatively the rate of fluid flowing from one or more activated fracture during a production test following a hydraulic stimulation.

15 GEOTHERMAL ENERGY↗

DOE OSTI2024

Utah FORGE 5-2557: Role of Fluid and Temperature in Fracture Mechanics and Couples THMC Processes for Enhanced Geothermal Systems - 2024 Annual Workshop Presentation

This is a presentation on the Role of Fluid and Temperature in Fracture Mechanics and Couples THMC Processes for Enhanced Geothermal Systems by Purdue University, presented by Laura Pyrak-Nolte. This video slide presentation describes the development and validation of a macroscopic model that can account for local deformation/friction behavior, seismic/aseismic behavior, chemical reactions, and determine the adequacy of classic Coulomb failure vs. rate-and-state friction. This presentation was featured in the Utah FORGE R&D Annual Workshop on August 13, 2024.

15 GEOTHERMAL ENERGY↗

DOE OSTI2017

Evaluation of CO 2 -Fluid-Rock Interaction in Enhanced Geothermal Systems: Field-Scale Geochemical Simulations

Recent studies suggest that using supercritical CO 2 (scCO 2 ) instead of water as a heat transmission fluid in Enhanced Geothermal Systems (EGS) may improve energy extraction. While CO 2 -fluid-rock interactions at “typical” temperatures and pressures of subsurface reservoirs are fairly well known, such understanding for the elevated conditions of EGS is relatively unresolved. Geochemical impacts of CO 2 as a working fluid (“CO 2 -EGS”) compared to those for water as a working fluid (H 2 O-EGS) are needed. The primary objectives of this study are (1) constraining geochemical processes associated with CO 2 -fluid-rock interactions under the high pressures and temperatures of a typical CO 2 -EGS site and (2) comparing geochemical impacts of CO 2 -EGS to geochemical impacts of H 2 O-EGS. The St. John’s Dome CO 2 -EGS research site in Arizona was adopted as a case study. A 3D model of the site was developed. Net heat extraction and mass flow production rates for CO 2 -EGS were larger compared to H 2 O-EGS, suggesting that using scCO 2 as a working fluid may enhance EGS heat extraction. More aqueous CO 2 accumulates within upper- and lower-lying layers than in the injection/production layers, reducing pH values and leading to increased dissolution and precipitation of minerals in those upper and lower layers. Dissolution of oligoclase for water as a working fluid shows smaller magnitude in rates and different distributions in profile than those for scCO 2 as a working fluid. It indicates that geochemical processes of scCO 2 -rock interaction have significant effects on mineral dissolution and precipitation in magnitudes and distributions.

58 GEOSCIENCES↗

DOE OSTI2024

Evaluation of sintered bauxite proppant for binary enhanced geothermal systems

Abstract Solid granular proppant particles are widely used in oil and gas development to sustain permeability through fractures after hydraulic stimulation. Similar proppants are of interest for geothermal applications where the goal of sustaining permeability is the same, but the harsh geothermal environment risks rapid proppant degradation that will reduce fracture permeability. Here, we present proppant conductivity experiments using saw cut granite, tensile fractured granite, and aluminum control specimens packed with sintered bauxite ceramic proppants at concentrations of 0.0, 0.1, and 1.0 kg/m 2 . Simulated geothermal conditions included temperatures up to 130 °C and normal closure stresses up to 60 MPa. Compared to unpropped specimens, peak fracture conductivity enhancement was up to 6 orders of magnitude. At simulated geothermal conditions, proppants were able to sustain fracture conductivity over 60 h, but chemical dissolution and decreasing permeability over time were evident. Irreversible conductivity reductions with crushing and embedment of proppants during loading stages were also observed. Overall, sintered bauxite proppant remains a promising option for low-temperature binary-cycle enhanced geothermal systems.

58 GEOSCIENCES↗

DOE OSTI2017

Discovering New Geothermal Systems In The Great Basin Region, Western USA: An Integrated Approach For Establishing Geothermal Play Fairways

The Great Basin of the western USA is capable of producing much greater amounts of geothermal energy than the current ~670 MW from ~25 power plants. Most geothermal resources in this region are blind, and thus the favorable characteristics for geothermal activity must be synthesized and methodologies developed to discover new commercial-grade systems (>130oC). The geothermal play fairway concept involves integration of multiple parameters indicative of geothermal activity as a means of identifying promising areas for new development. In the Nevada play fairway project, nine geologic, geochemical, and geophysical parameters were initially synthesized to produce a new geothermal potential map of 96,000 km2. These parameters were grouped into subsets and individually weighted to delineate rankings for heat and local, intermediate, and regional permeability, which collectively defined the play fairways. From the regional map, 24 highly prospective areas, including known undeveloped systems and unknown potential blind systems, were identified for further analysis. Five particularly promising sites were then selected for detailed studies. Multiple techniques, including geologic mapping, Quaternary fault analysis, 2-m temperature surveys, gravity surveys, LiDAR, geochemical studies, seismic reflection analysis, and 3D modeling, were employed in these areas to define likely sites for high permeability and define highly prospective drilling targets. Local and intermediate permeability models were revised to reflect results of detailed analyses and generate new detailed play fairway maps. Lessons learned include: 1) initially identified sites commonly include multiple favorable settings at a finer scale; 2) promising sites in Cenozoic basins cannot be recognized without detailed geophysical surveys; and 3) play fairway analysis is critical at multiple scales, providing a means to select regional prospects as well as vectoring into drilling targets at individual sites. Based on our detailed studies, several potential new, high temperature systems were discovered. However, TG drilling is needed to confirm commercial grade resources.

15 GEOTHERMAL ENERGY↗

DOE OSTI2014

Towards the Understanding of Induced Seismicity in Enhanced Geothermal Systems

This DOE funded project was a collaborative effort between Array Information Technology (AIT), the University of California at Berkeley (UCB), the Helmholtz Centre Potsdam - German Research Center for Geosciences (GFZ) and the Lawrence Berkeley National Laboratory (LBNL). It was also part of the European research project “GEISER”, an international collaboration with 11 European partners from six countries including universities, research centers and industry, with the goal to address and mitigate the problems associated with induced seismicity in Enhanced Geothermal Systems (EGS). The goal of the current project was to develop a combination of techniques, which evaluate the relationship between enhanced geothermal operations and the induced stress changes and associated earthquakes throughout the reservoir and the surrounding country rock. The project addressed the following questions: how enhanced geothermal activity changes the local and regional stress field; whether these activities can induce medium sized seismicity M > 3; (if so) how these events are correlated to geothermal activity in space and time; what is the largest possible event and strongest ground motion, and hence the potential hazard associated with these activities. The development of appropriate technology to thoroughly investigate and address these questions required a number of datasets to provide the different physical measurements distributed in space and time. Because such a dataset did not yet exist for an EGS system in the United State, we used current and past data from The Geysers geothermal field in northern California, which has been in operation since the 1960s. The research addressed the need to understand the causal mechanisms of induced seismicity, and demonstrated the advantage of imaging the physical properties and temporal changes of the reservoir. The work helped to model the relationship between injection and production and medium sized magnitude events that have jeopardized, and in some cases suspended, the generation of energy from EGS systems worldwide.

15 GEOTHERMAL ENERGY↗

DOE OSTI2018

Microseismicity cloud can be substantially larger than the associated stimulated fracture volume: the case of the Paralana Enhanced Geothermal System

Here, the goal of hydraulic stimulation is to increase formation permeability in the near vicinity of a well. However, there remain technical challenges around measuring the outcome of this operation. During two Enhanced Geothermal System (EGS) stimulations in South Australia, Paralana in 2011 and Habanero in 2003, extensive catalogs of microseismicity were recovered. It is often assumed that shear failure of existing fractures is the main mechanism behind both the induced earthquakes and any permeability enhancement. This underpins a common notion, that the seismically active volume is also the stimulated reservoir. In this paper, we compute the density of earthquake hypocenters and provide evidence that, under certain conditions, this spatiotemporal quantity is a reasonable proxy for pore pressure increase. We then apply an inverse modeling approach that uses the earthquake observations and a modified reservoir simulator to estimate the parameters of a permeability evolution relation. The regime implied by the data indicates that most permeability enhancement occurred very near to the wellbore and was not coincident with the bulk of the seismicity, whose volume was about two orders of magnitude larger. Thus, we conclude that, in some cases, it is possible for permeability enhancement and induced seismicity to be decoupled, in which case the seismically active volume is a poor indicator of the stimulated reservoir. Our results raise serious questions about the effectiveness of hydroshearing as a stimulation mechanism in EGS. Finally, this study extends our understanding of the complex processes linking earthquakes, fluid pressure, and permeability in both natural and engineered settings.

58 GEOSCIENCES↗

DOE OSTI2023

Evaluating the Impact of Redox Potential on the Corrosion of Q125, 316L, and C276 Steel in Low-Temperature Geothermal Systems

Time series experiments were used to explore the fluid redox impact on the corrosion of Q125, 316L, and C276 steels in low-ionic-strength and neutral water at temperature and pressure conditions associated with low-temperature geothermal systems. After exposing polished samples of each steel grade to an oxidizing (H2O2) and a reducing (Zn-doped) fluid for intervals of 24 h, 1 week, and 6 weeks, the atomic force microscopy results revealed general corrosion for Q125, while 316L and C276 exhibited pitting, crevice expansion, and edge attack corrosion. Secondary depositional features are frequently found as topographic highs, adjacent to pitting corrosion. These features may be identified as there is a very strong spatial correlation between the height retrace and phase retrace surface maps. All steels became progressively rougher over time after exposure to both fluids, while the corrosion rates were more complex. Samples exposed to the reducing fluid experienced an increase in the corrosion rate over time, while C276 and 316L experienced a decrease in the corrosion rate. Finally, a novel data validation technique was developed to address the intrinsic scalability of corrosion. The results indicate that the AFM scan area does not affect the measured surface roughness over nearly three orders of magnitude.

Bowman, Samuel (ORCID:000000021510174X)↗

DOE OSTI2022

Computed Tomography Scanning and Geophysical Measurements of the Enhanced Geothermal Systems (EGS) Collab SURF Core

The computed tomography (CT) facilities and the Multi-Sensor Core Logger (MSCL) at the National Energy Technology Laboratory (NETL) in Morgantown, West Virginia were used to characterize core from 8 wells from the Enhanced Geothermal Systems (EGS) Collab project located in the Sanford Underground Research Facility’s (SURF) 4850 level. The work in this report falls in Experiment 1 in a three-phase experiment, with the primary purpose to increase understanding of hydraulic fracturing. The primary impetus of this work is a collaboration between U.S. Department of Energy (DOE) and the EGS Collab. The resultant datasets are presented in this report and can be accessed from NETL's Energy Data eXchange (EDX) online system using the following link: https://edx.netl.doe.gov/dataset/surf-collab-core. All equipment and techniques used were non-destructive, enabling future examinations and analyses to be performed on these cores. None of the equipment used was suitable for direct visualization of the pore space in the core, although fractures and discontinuities were detectable with the methods tested. Low resolution CT imagery with the NETL medical CT scanner was performed on the entire core. Qualitative analysis of the medical CT images, coupled with X-ray fluorescence (XRF), P-wave, and magnetic susceptibility measurements from the MSCL were useful in identifying zones of interest for more detailed analysis as well as fractured zones. The ability to quickly identify key areas for more detailed study with higher resolution will save time and resources in future studies. The combination of methods used provides a multi-scale analysis of the core; the resulting macro and micro descriptions are relevant to many subsurface energy related examinations traditionally performed at NETL.

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

Alternative, Less Water-Intensive, Fracturing Fluids for Enhanced Geothermal Systems

Four fracturing fluids; water, CO2, CO2 with water, and CO2 with an aqueous solution of a CO2-reactive polymer, poly(allylamine) (PAA, 1wt%) were evaluated using a high-temperature true-triaxial fracturing apparatus and ½ foot side granite cubic samples. All three CO2-based fracturing fluids, CO2, CO2 with water, and CO2 with aqueous PAA fractured granite at higher breakdown pressures, high transient flow rates, and produce higher-conductivity fractures as compared to water. Additionally, faster pressurization rates with CO2-based fracturing fluids (obtained when fracturing at constant flow rate mode) are found to be associated with higher fracture conductivities. When partially saturating the rock sample with PAA solution followed by fracturing with CO2, the volume expansion caused by CO2-induced cross-linking of PAA leads to a faster pressure increase due to the associated stress generated and increase in viscosity. It was also found that CO2 as a fracturing fluid injected in hot dry rock (HDR) attain the highest fracture conductivity only when injected at very high flow rates, followed very closely by the CO2/PAA fracturing fluid system that generates fractures with, on average, similarly high conductivity values though independently of injection flow rate and using 1/6 of the mass of CO2 as compared to CO2 in HDR. Breakdown pressures were also similar for CO2 stimulation in HDR and CO2/PAA fluid system under identical injection flow rates. It is concluded that CO2 (when injected in HDR) and CO2/PAA are the fluids of choice for stimulation of granitic rock samples under the studied geothermal P/T conditions. CO2/PAA, however, offer the following three additional advantages; 1) it requires significantly lower volumes of CO2, 2) fracture permeability is independent of injection flow rate, and 3) the reversible (previously reported) viscosity increase is beneficial to transport proppants if they are ever developed enhanced geothermal systems.

Jian, Guoqing↗

DOE OSTI2016

The importance of earthquake interactions for injection-induced seismicity: Retrospective modeling of the Basel Enhanced Geothermal System

We explore the role of earthquake interactions during an injection-induced seismic sequence. We propose a model, which considers both a transient pressure and static stress redistribution due to event interactions as triggering mechanisms. By calibrating the model against observations at the Enhanced Geothermal System of Basel, Switzerland, we are able to reproduce the time behavior of the seismicity rate. We observe that considering earthquake interactions in the modeling leads to a larger number of expected seismic events (24% more) if compared to a pressure-induced seismicity only. The increase of the number of events is particularly evident after the end of the injection. Finally, we conclude that implementing a model for estimating the static stress changes due to mutual event interactions increases significantly the understanding of the process and the behavior of induced seismicity.

58 GEOSCIENCES↗

DOE OSTI2017

Geothermal System Extensions

This material is based upon work supported by the Department of Energy under Award Number DE-EE0000318. The City of Boise operates and maintains the nation’s largest geothermal heating district. Today, 91 buildings are connected, providing space heating to over 5.5 million square feet, domestic water heating, laundry and pool heating, sidewalk snowmelt and other related uses. Approximately 300 million gallons of 177°F geothermal water is pumped annually to buildings and institutions located in downtown Boise. The closed loop system returns all used geothermal water back into the aquifer after heat has been removed via an Injection Well. Water injected back into the aquifer has an average temperature of 115°F. This project expanded the Boise Geothermal Heating District (Geothermal System) to bring geothermal energy to the campus of Boise State University and to the Central Addition Eco-District. In addition, this project also improved the overall system’s reliability and increased the hydraulic capacity.

15 GEOTHERMAL ENERGY↗

DOE OSTI2015

Enhanced Geothermal System (EGS) Infographic

The EGS infographic provides an overview of this burgeoning technology that could access an enormous, domestic, clean energy resource predicted at more than 100 GW in the United States alone, according to an MIT study. To take advantage of this vast resource, the U.S. Department of Energy’s (DOE) Geothermal Technologies Office (GTO) promotes and invests in industry, academia, and the national laboratories to develop and demonstrate EGS throughout the United States.

enhanced geothermal systems↗

DOE OSTI2015

Final Progress Report for Project Entitled: Quantum Dot Tracers for Use in Engineered Geothermal Systems

The objective of this project was to develop and demonstrate a new class of tracers that offer great promise for use in characterizing fracture networks in EGS reservoirs. From laboratory synthesis and testing through numerical modeling and field demonstrations, we have demonstrated the amazing versatility and applicability of quantum dot tracers. This report summarizes the results of four years of research into the design, synthesis, and characterization of semiconductor nanocrystals (quantum dots) for use as geothermal tracers.

15 GEOTHERMAL ENERGY↗

DOE OSTI2013

Life Cycle Water Consumption and Water Resource Assessment for Utility-Scale Geothermal Systems: An In-Depth Analysis of Historical and Forthcoming EGS Projects

This report is the third in a series of reports sponsored by the U.S. Department of Energy Geothermal Technologies Program in which a range of water-related issues surrounding geothermal power production are evaluated. The first report made an initial attempt at quantifying the life cycle fresh water requirements of geothermal power-generating systems and explored operational and environmental concerns related to the geochemical composition of geothermal fluids. The initial analysis of life cycle fresh water consumption of geothermal power-generating systems identified that operational water requirements consumed the vast majority of water across the life cycle. However, it relied upon limited operational water consumption data and did not account for belowground operational losses for enhanced geothermal systems (EGSs). A second report presented an initial assessment of fresh water demand for future growth in utility-scale geothermal power generation. The current analysis builds upon this work to improve life cycle fresh water consumption estimates and incorporates regional water availability into the resource assessment to improve the identification of areas where future growth in geothermal electricity generation may encounter water challenges. This report is divided into nine chapters. Chapter 1 gives the background of the project and its purpose, which is to assess the water consumption of geothermal technologies and identify areas where water availability may present a challenge to utility-scale geothermal development. Water consumption refers to the water that is withdrawn from a resource such as a river, lake, or nongeothermal aquifer that is not returned to that resource. The geothermal electricity generation technologies evaluated in this study include conventional hydrothermal flash and binary systems, as well as EGSs that rely on engineering a productive reservoir where heat exists, but where water availability or permeability may be limited. Chapter 2 describes the approach and methods for this work and identifies the four power plant scenarios evaluated: a 20-MW EGS binary plant, a 50-MW EGS binary plant, a 10-MW hydrothermal binary plant, and a 50-MW hydrothermal flash plant. The methods focus on (1) the collection of data to improve estimation of EGS stimulation volumes, aboveground operational consumption for all geothermal technologies, and belowground operational consumption for EGS; and (2) the mapping of the geothermal and water resources of the western United States to assist in the identification of potential water challenges to geothermal growth. Chapters 3 and 4 present the water requirements for the power plant life cycle. Chapter 3 presents the results of the current data collection effort, and Chapter 4 presents the normalized volume of fresh water consumed at each life cycle stage per lifetime energy output for the power plant scenarios evaluated. Over the life cycle of a geothermal power plant, from construction through 30 years of operation, the majority of water is consumed by plant operations. For the EGS binary scenarios, where dry cooling was assumed, belowground operational water loss is the greatest contributor depending upon the physical and operational conditions of the reservoir. Total life cycle water consumption requirements for air-cooled EGS binary scenarios vary between 0.22 and 1.85 gal/kWh, depending upon the extent of belowground operational water consumption. The air-cooled hydrothermal binary and flash plants experience far less fresh water consumption over the life cycle, at 0.04 gal/kWh. Fresh water requirements associated with air- cooled binary operations are primarily from aboveground water needs, including dust control, maintenance, and domestic use. Although wet-cooled hydrothermal flash systems require water for cooling, these plants generally rely upon the geofluid, fluid from the geothermal reservoir, which typically has high salinity and total dissolved solids concentration and is much warmer than normal groundwater sources, for their cooling water needs; thus, while there is considerable geofluid loss at 2.7 gal/kWh, fresh water consumption during operations is similar to that of aircooled binary systems. Chapter 5 presents the assessment of water demand for future growth in deployment of utility-scale geothermal power generation. The approach combines the life cycle analysis of geothermal water consumption with a geothermal supply curve according to resource type, levelized cost of electricity (LCOE), and potential growth scenarios. A total of 17 growth scenarios were evaluated. In general, the scenarios that assumed lower costs for EGSs as a result of learning and technological improvements resulted in greater geothermal potential, but also significantly greater water demand due to the higher water consumption by EGSs. It was shown, however, that this effect could be largely mitigated if nonpotable water sources were used for belowground operational water demands. The geographical areas that showed the highest water demand for most growth scenarios were southern and northern California, as well as most of Nevada. In addition to water demand by geothermal power production, Chapter 5 includes data on water availability for geothermal development areas. A qualitative analysis is included that identifies some of the basins where the limited availability of water is most likely to affect the development of geothermal resources. The data indicate that water availability is fairly limited, especially under drought conditions, in most of the areas with significant near- and medium-term geothermal potential. Southern California was found to have the greatest potential for water-related challenges with its combination of high geothermal potential and limited water availability. The results of this work are summarized in Chapter 6. Overall, this work highlights the importance of utilizing dry cooling systems for binary and EGS systems and minimizing fresh water consumption throughout the life cycle of geothermal power development. The large resource base for EGSs represents a major opportunity for the geothermal industry; however, depending upon geology, these systems can require large quantities of makeup water due to belowground reservoir losses. Identifying potential sources of compatible degraded or low-quality water for use for makeup injection for EGS and flash systems represents an important opportunity to reduce the impacts of geothermal development on fresh water resources. The importance of identifying alternative water sources for geothermal systems is heightened by the fact that a large fraction of the geothermal resource is located in areas already experiencing water stress. Chapter 7 is a glossary of the technical terms used in the report, and Chapters 8 and 9 provide references and a bibliography, respectively.

15 GEOTHERMAL ENERGY↗

DOE OSTI2013

Life Cycle Water Consumption and Water Resource Assessment for Utility-Scale Geothermal Systems: An In-Depth Analysis of Historical and Forthcoming EGS Projects

15 GEOTHERMAL ENERGY↗

DOE OSTI2013

Application of 2D VSP Imaging Technology to the Targeting of Exploration and Production Wells in a Basin and Range Geothermal System

The Humboldt House-Rye Patch geothermal resource area (HH-RP) comprises approximately 12,000 acres along and west of the Humboldt Range, adjacent to the Rye Patch Reservoir. A Federal Geothermal Unit covers essentially all of the known shallow thermal anomaly at the site, and the Operator, Presco Energy, is in the process of completing wellfield development adjacent to the Rye Patch binary plant, a nominal 17-megawatt system in the southern Unit area. DOE award EE0002840, made under the auspices of the Geothermal Technologies Program, was originally approved in January of 2010, and used a VSP profiling technology to improve seismic imaging in the Basin and Range. Phase I field activities were conducted in the 3rd quarter of 2010, and both the Phase I report and a supplemental report were completed in March and April of 2011. Two targets were identified for tests of upflow structures, both using existing wellbores, originally the 51-21 and 52-28, in the Rye Patch wellfield. The Phase II validation was approved by DOE in May of 2011.

15 GEOTHERMAL ENERGY↗