Search Results (72)

Thermal stimulation represents an effective method for enhancing reservoir permeability, thereby improving geothermal energy recovery in Enhanced Geothermal Systems (EGS). The phase-field method (PFM) has been widely adopted for its proven capability in modeling the fracture behavior of brittle solids. Consequently, a coupled thermo-mechanical phase-field model (TM-PFM) was developed in COMSOL 6.2 Multiphysics to probe thermal fracturing mechanisms in reservoir rocks. The TM-PFM was validated against the analytical solutions for the temperature and stress fields under steady-state heat conduction in a thin-walled cylinder, three-point bending tests, and thermal shock tests. Subsequently, two distinct thermal fracturing modes in reservoir rock under high-temperature conditions were investigated: (i) fracture initiation driven by sharp temperature gradients during instantaneous thermal shocks, and (ii) crack propagation resulting from heterogeneous thermal expansion of constituent minerals. The proposed TM-PFM has been validated through systematic comparison between the simulation results and the corresponding experimental data, thereby demonstrating its capability to accurately simulate thermal fracturing. These findings provide mechanistic insights for optimizing geothermal energy extraction in EGS. Full article

Enhanced Geothermal Systems (EGS) require thermochemically stable proppant materials capable of sustaining fracture conductivity under harsh subsurface conditions. This study systematically investigates the response of commercial proppants to coupled thermo-hydro-chemical (THC) effects, focusing on chemical stability and microstructural evolution. Four proppant types were evaluated: an ultra-low-density ceramic (ULD), a resin-coated sand (RCS), and two quartz-based silica sands. Experiments were conducted under simulated EGS conditions at 130 °C with daily thermal cycling over a 25-day period, using diluted site-specific Utah FORGE geothermal fluids. Static batch reactions were followed by comprehensive multi-modal characterization, including scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and micro-computed tomography (micro-CT). Proppants were tested in both granular and powdered forms to evaluate surface area effects and potential long-term reactivity. Results indicate that ULD proppants experienced notable resin degradation and secondary mineral precipitation within internal pore networks, evidenced by a 30.4% reduction in intragranular porosity (from CT analysis) and diminished amorphous peaks in the XRD spectra. RCS proppants exhibited a significant loss of surface carbon content from 72.98% to 53.05%, consistent with resin breakdown observed via SEM imaging. While the quartz-based sand proppants remained morphologically intact at the macro-scale, SEM-EDS revealed localized surface alteration and mineral precipitation. The brown sand proppant, in particular, showed the most extensive surface precipitation, with a 15.2% increase in newly detected mineral phases. These findings advance understanding of proppant–fluid interactions under low-temperature EGS conditions and underscore the importance of selecting proppants based on thermo-chemical compatibility. The results also highlight the need for continued development of chemically resilient proppant formulations tailored for long-term geothermal applications. Full article

In the operation of enhanced geothermal systems (EGSs), complex physical and chemical coupling processes, which are crucial for the efficient exploitation of geothermal energy, are involved. In situ studies of multi-fracture hot dry rocks (HDRs) face significant challenges, leading to a shortage of experimental data for verifying numerical simulations and supporting experimental techniques. In this paper, a multi-field coupling experimental simulation technique was designed for a multi-fracture geothermal reservoir. This technique enables the experimental investigation of the effects of fracture and reservoir characteristics, working fluid parameters, and wellbore arrangement on the multi-field coupling transport mechanism inside geothermal reservoirs during EGS operation. In addition, the practicability and reliability of the experimental technique were proved via a two-dimensional multi-fracture model. The experimental technique addresses a research gap in studying multi-fracture geothermal reservoirs and holds potential to promote substantial progress in geothermal resource exploitation. Full article

Enhanced or engineered geothermal systems (EGSs), or non-hydrothermal resources, are highly notable among sustainable energy resources because of their abundance and cleanness. The EGS concept has received worldwide attention and undergone intensive studies in the last decade in the US and around the world. In comparison, hydrothermal reservoir resources, the ‘low-hanging fruit’ of geothermal energy, are very limited in amount or availability, while EGSs are extensive and have great potential to supply the entire world with the needed energy almost permanently. The EGS, in essence, is an engineered subsurface heat mining concept, where water or another suitable heat exchange fluid is injected into hot formations to extract heat from the hot dry rock (HDR). Specifically, the EGS relies on the principle that injected water, or another working fluid, penetrates deep into reservoirs through fractures or high-permeability channels to absorb large quantities of thermal energy by contact with the host hot rock. Finally, the heated fluid is produced through production wells for electricity generation or other usages. Heat mining from fractured EGS reservoirs is subject to complex interactions within the reservoir rock, involving high-temperature heat exchange, multi-phase flow, rock deformation, and chemical reactions under thermal-hydrological-mechanical (THM) processes or thermal-hydrological-mechanical-chemical (THMC) interactions. In this paper, we will present a THM model and reservoir simulator and its application for simulation of hydrothermal geothermal systems and EGS reservoirs as well as a methodology of coupling thermal, hydrological, and mechanical processes. A numerical approach, based on discretizing the thermo-poro-elastic Navier equation using an integral finite difference method, is discussed. This method provides a rigorous, accurate, and efficient fully coupled methodology for the three (THM) strongly interacted processes. Several programs based on this methodology are demonstrated in the simulation cases of geothermal reservoirs, including fracture aperture enhancement, thermal stress impact, and tracer transport in a field-scale reservoir. Results are displayed to show geomechanics’ impact on fluid and heat flow in geothermal reservoirs. Full article

In hot dry rocks (HDRs), hydraulic fracturing is necessary to create enhanced geothermal systems (EGSs) and optimize flow rates between injection and production wells. The geometry of the induced fracture is related to numerous factors, including rock mechanical properties, especially Young’s modulus and Poisson’s ratio. In this paper, we show the influence of Young’s and Poisson’s parameters on fracture geometry in selected HDR-type prospective areas in Poland. Parameters were determined in the laboratory based on drill core samples from granite and sandstone formations using both dynamic and static methods. The results obtained reveal strong differences between dynamic and static values in granite and less diverse results in sandstone. Based on these data, numerical simulations of fracture geometry were carried out, taking into account the variability in the rocks’ elastic parameters. Sensitivity analysis showed that relatively high diversity in the elastic parameters led to a relatively slight impact on the fracture geometry of the tested formations. The influence of Young’s modulus did not exceed 6.5% of the reference half-length and width values for sandstone and 7.3% of the half-length for granite. Variability in the fracture width was significant in granite formation and amounted to 46.4%. The influence of Poisson’s ratio was marginal in both tested types of rocks. The research results, which have not been reported previously, can be considered for the design of hydraulic fracturing operations in enhanced geothermal systems in Poland. Full article

The work aims to give a preliminary investigation of the geothermal potentiality of the hot dry granitic rocks in the Hail area, Northern KSA. The Hail area is characterized by a massive exposed belt of radioactive granitic rocks in the southern part, while the northern part is covered by a sedimentary section. A comprehensive methodology utilizing different categories of mineralogical petrographic, geochemical, geophysical well logging and, radiometry datasets, was used to assess the radiogenic heat production capacity of this granite. The measured data are integrated and interpreted to quantify the potential geothermal capacity of the granite and estimate its possible power production. The radioactivity and radiogenic heat production (RHP) of the Hail granites are among the highest recorded values in Saudi Arabia. Land measurements indicate uranium, thorium, potassium, and RHP values of 17.80 ppm, 90.0 ppm, 5.20%, and 11.93 µW/m³, respectively. The results indicated the presence of a reasonable subsurface geothermal reservoir condition with heat flow up to 99.87 mW/M² and a reservoir temperature of 200 °C (5 km depth). Scenarios for energy production through injecting water and high-pressure CO₂ in the naturally/induced fractured rock are demonstrated. Reserve estimate revealed that at a 2% heat recovery level, the Hail granites could generate about 3.15 × 10¹⁶ MWe, contributing to an average figure of 3.43 × 10¹² kWh/y, for annual energy per capita Saudi share. The results of this study emphasized the potential contribution of the Hail granite in the future of the energy mix of KSA, as a new renewable and sustainable resource. It is recommended to enhance the surface geophysical survey in conjunction with a detailed thermo-mechanical laboratory investigation to delineate the subsurface orientation and geometry of the granite and understand its behavior under different temperature and pressure conditions. Full article

Geothermal energy and hot dry rock (HDR), as an important clean energy technology, have garnered widespread attention globally in recent years. Enhanced Geothermal Systems (EGS), a technology for extracting energy from low-permeability Hot Dry Rock (HDR) reservoirs, is crucial for the utilization of geothermal energy. Although interest in this area has significantly increased, a comprehensive and systematic analysis providing a clear understanding of the development context is still lacking. To this end, this paper presents a bibliometric analysis of 1764 relevant publications from 1996 to 2023, revealing research trends and hotspots in this field. Utilizing tools such as Bibliometrix (Version 4.2.3), CiteSpace (Version 6.2.R2), and VOSviewer (Version 1.6.19), the study analyzes publication trends, subject categories, journals, authors, institutions, and national contributions. The results indicate that EGS technology, rock mechanical behavior, and environmental impact assessment are the primary research hotspots, with China being the leading country in terms of publication volume. Future research directions include technological optimization, environmental sustainability, and the advancement of interdisciplinary collaboration. This study provides a valuable reference for further research and application in geothermal energy and HDR and offers a dynamic perspective on shifting research priorities. Full article

Geothermal energy has the advantages of being green, stable, abundant, and renewable. The thermal energy extraction efficiency of an enhanced geothermal system (EGS) is significantly regulated by Thermo–Hydraulic (TH) processes. To accurately evaluate the long-term heat recovery performance of an EGS, the dynamic influence mechanisms under multi-field TH coupling effects must be considered comprehensively. Therefore, in this study, based on the local thermal equilibrium theory, a temperature–seepage coupling model is established using the COMSOL software. The influences of reservoir parameters and fractures on the geothermal energy mining effect are studied, and the distribution law of temperature and pressure in the thermal reservoir is analyzed. The research results provide a reference for EGS reservoir reconstruction and heat recovery efficiency optimization. It is shown that the temperature difference near the injection–production well in the early stage of development leads to the slow recovery of thermal reservoir pressure. When the matrix permeability is greater than 455 mD, the temperature of the production fluid drops too quickly, and the development life of the thermal reservoir is short. The matrix porosity has little effect on the development of thermal reservoirs. When the porosity increases from 0.05 to 0.3, after 40 years of production, the mass flow rate of the produced fluid increases by 3.08%, the temperature of the produced fluid increases by 2.14%, and the heat recovery rate increases by 7.04%. The number of fractures has a significant influence on the development of thermal reservoirs. When the number of fractures increases from 0 to 3, the mass flow rate of production fluid increases by 55.9%, the thermal breakthrough is rapid, and the development life of the thermal reservoir is shortened. Notably, the unreasonable use of cracks will hinder the outward spread of the injected fluid. Full article

The reserves of hot dry rock (HDR) geothermal resources are huge. The main method used to develop HDR geothermal resources is called an enhanced geothermal system (EGS), and this generally uses hydraulic fracturing. After nearly 50 years of research and development, more and more countries have joined the ranks engaged in the exploration and development of HDR in the world. This paper summarizes the base technologies, key technologies, and game-changing technologies used to promote the commercialization of HDR geothermal resources. According to the present situation of the exploration, development, and utilization of HDR at home and abroad, the evaluation and site selection, efficient and low-cost drilling, and geothermal utilization of HDR geothermal resources are defined as the base technologies. Key technologies include the high-resolution exploration and characterization of HDR, efficient and complex fracture network reservoir creation, effective microseismic control, fracture network connectivity, and reservoir characterization. Game-changing technologies include downhole liquid explosion fracture creation, downhole in-situ efficient heat transfer and power generation, and the use of CO₂ and other working fluids for high-efficient power generation. Most of the base technologies already have industrial applications, but future efforts must focus on reducing costs. The majority of key technologies are still in the site demonstration and validation phase and have not yet been applied on an industrial scale. However, breakthroughs in cost reduction and application effectiveness are urgently needed for these key technologies. Game-changing technologies remain at the laboratory research stage, but any breakthroughs in this area could significantly advance the efficient development of HDR geothermal resources. In addition, we conducted a comparative analysis of the respective advantages of China and the United States in some key technologies of HDR development. On this basis, we summarized the key challenges identified throughout the discussion and highlighted the most pressing research priorities. We hope these technologies can guide new breakthroughs in HDR geothermal development in China and other countries, helping to establish a batch of HDR exploitation demonstration areas. In addition, we look forward to fostering collaboration between China and the United States through technical comparisons, jointly promoting the commercial development of HDR geothermal resources. Full article

This paper reviews recent advancements in integrated thermoelectric power generation and water desalination technologies, driven by the increasing global demand for electricity and freshwater. The growing population and reliance on fossil fuels for electricity generation pose challenges related to environmental pollution and resource depletion, necessitating the exploration of alternative energy sources and desalination techniques. While thermoelectric generators are capable of converting low-temperature thermal energy into electricity and desalination processes that can utilize low-temperature thermal energy, their effective integration remains largely unexplored. Currently available hybrid power and water systems, such as those combining conventional heat engine cycles (e.g., the Rankine and Kalina cycles) with reverse osmosis, multi-effect distillation, and humidification–dehumidification, are limited in effectively utilizing low-grade thermal energy for simultaneous power generation and desalination, while solid-state heat-to-work conversion technology, such as thermoelectric generators, have low heat-to-work conversion efficiency. This paper identifies a key research gap in the limited effective integration of thermoelectric generators and desalination, despite their complementary characteristics. The study highlights the potential of hybrid systems, which leverage low-grade thermal energy for simultaneous power generation and desalination. The review also explores emerging material innovations in high figure of merit thermoelectric materials and advanced MD membranes, which could significantly enhance system performance. Furthermore, hybrid power–desalination systems incorporating thermoelectric generators with concentrated photovoltaic cells, solar thermal collectors, geothermal energy, and organic Rankine cycles (ORCs) are examined to highlight their potential for sustainable energy and water production. The findings underscore the importance of optimizing material properties, system configurations, and operating conditions to maximize efficiency and output while reducing economic and environmental costs. Full article

Geothermal energy is a sustainable resource, specifically referenced as a key energy resource in the Trump adminstration’s Declaring a National Energy Emergency Executive Order in 2025, that harnesses heat from the Earth’s crust to provide continuous clean energy. Identifying suitable geothermal sites involves evaluating various geological and geographical factors to ensure optimal resource extraction and minimal environmental impact. This study evaluates potential geothermal sites in South and Southwestern US states with a high concentration of abandoned fossil fuel infrastructure, tribal lands, HUBZones, or all three in order to evaluate how to balance resource development, tribal land rights, and environmental justice in future geothermal energy systems. First, we used publicly available Geographic Information System (GIS) datasets to identify areas that are tribal lands, HUBZones, and/or have orphaned fossil fuel infrastructure. Then, we leveraged geothermal potential GIS datasets to classify subsurface temperatures and calculated how much energy enhanced geothermal system (EGS) technology could produce in these areas using methods from the geothermal literature. The analysis identified promising geothermal sites that overlap with tribal lands, HUBZones, and existing fossil fuel infrastructure in the following states: Arizona, New Mexico, Texas, Louisiana, Mississippi, Nevada, Arkansas, and Oklahoma. These states have at least a technical potential of over 2300 GW and have over 18,000 abandoned oil wells that could be converted into geothermal plants. This potential could contribute significantly to the nation’s renewable energy portfolio while simultaneously providing additional revenue opportunities and environmental remediation to tribal lands and low-income communities by leveraging policies and programs like the Indian Energy Purchase Preference (IEPP) and the Historically Underutilized Business Zone program (HUBZone), respectively. Full article

This study evaluates the potential of enhanced geothermal systems (EGSs) in Poland, focusing on formations composed by igneous rocks, such as crystalline rocks of the Karkonosze pluton and volcanic rocks of the Gorzów Block. A total of 57 rock samples, including granites and rhyolites from these formations, were analyzed for their thermal and geochemical properties to assess their suitability for EGS development. The results highlight the importance of thermal parameters, such as conductivity and diffusivity, in optimizing geothermal exploitation. The measurements reveal that Karkonosze granite exhibits high thermal diffusivity and conductivity, making it a prime candidate for heat extraction. Although the Gorzów Block rhyolites show slightly lower values, their high initial temperatures still promise long-term geothermal viability. Geochemical modelling indicates that mineral precipitation that causes permeability damage is unlikely in these reservoirs. Instead, minor increases in porosity due to mineral dissolution can reduce hydraulic resistance, potentially affecting the performance of the system. Full article

This study aims to better harness the geothermal potential of Mount Meager in British Columbia, a premier reserve of geothermal resources in Canada. Numerical investigations explore the feasibility and optimization of an Enhanced Geothermal System to boost geothermal energy extraction capabilities. Utilizing COMSOL Multiphysics, the model simulates non-isothermal fluid flow and heat transfer through complex subsurface geology with discrete fracture planes. The sensitivity analyses assess the impact of various operational parameters, including injection strategies, reservoir characteristics, and wellbore configurations on heat extraction efficiency. These analyses indicate that a higher injection rate, lower injection temperatures, and optimized fracture areas significantly enhance system performance by maximizing thermal energy capture and minimizing thermal breakthrough. Additionally, specific wellbore configurations, particularly the triplet setup with deeper depth, significantly improve geothermal fluid circulation and heat extraction compared to doublet configurations at shallower depths. This study reveals that the base case scenario of the EGS could generate approximately $8.311\times {10}^9$ kWh over 30 years, while optimization strategies could elevate potential production to up to $16.68\times {10}^9$ kWh. These findings underscore the critical role of carefully designed operational strategies that leverage local geological and thermal characteristics to optimize geothermal systems, thereby enhancing efficiency and promoting sustainable energy development at Mount Meager. Full article

With the continuous increase in global greenhouse gas emissions, the impacts of climate change are becoming increasingly severe. In this context, geothermal energy has gained significant attention due to its numerous advantages. Alongside advancements in CO₂ geological sequestration technology, the use of CO₂ as a working fluid in geothermal systems has emerged as a key research focus. Compared to traditional water-based working fluids, CO₂ possesses lower viscosity and higher thermal expansivity, enhancing its mobility in geothermal reservoirs and enabling more efficient heat transfer. Using CO₂ as a working fluid not only improves geothermal energy extraction efficiency but also facilitates the long-term sequestration of CO₂ within reservoirs. This paper reviews recent research progress on the use of CO₂ as a working fluid in Enhanced Geothermal Systems (EGS), with a focus on its potential advantages in improving heat exchange efficiency and power generation capacity. Additionally, the study evaluates the mineralization and sequestration effects of CO₂ in reservoirs, as well as its impact on reservoir properties. Finally, the paper discusses the technological developments and economic analyses of integrating CO₂ as a working fluid with other technologies. By systematically reviewing the research on CO₂ in EGS, this study provides a theoretical foundation for the future development of geothermal energy using CO₂ as a working fluid. Full article

This paper presents a comprehensive analysis of supercritical carbon dioxide (sCO₂)-enhanced geothermal systems (EGSs) in Poland, focusing on their energetic performance through process modeling and optimization. EGSs harness the potential of geothermal energy by utilizing supercritical carbon dioxide as the working fluid, offering promising avenues for sustainable power generation. This study investigates two distinct configurations of sCO₂-EGS: one dedicated to power generation via a binary system with an organic Rankine cycle and the other for combined power and heat production through a direct sCO₂ cycle. Through accurate process modeling and simulation, key parameters influencing system efficiency and performance are identified and optimized. The analysis integrates thermodynamic principles with geological and operational constraints specific to the Polish context. The results highlight the potential of sCO₂-EGSs to contribute to the country’s energy transition, offering insights into the optimal design and operation of such systems for maximizing both power and thermal output while ensuring economic viability and environmental sustainability. Full article