An enhanced geothermal system(EGS)represents a promising approach to sustainable energy generation by harnessing subsurface heat from deep geological formations with low natural permeability.Sedimentary basins-such as...An enhanced geothermal system(EGS)represents a promising approach to sustainable energy generation by harnessing subsurface heat from deep geological formations with low natural permeability.Sedimentary basins-such as the Williston Basin in North Dakota-are considered viable candidates for EGS development due to their broad geographic extent and moderate geothermal potential.Notably,depleted or non-productive oil wells within these basins offer a cost-effective opportunity for EGS implementation as they can be repurposed,thereby significantly reducing the need for new drilling.This study evaluates the feasibility of EGS deployment in McKenzie County,North Dakota.Core samples from five partially abandoned or dry oil wells associated with production from the Red River Formation were obtained from the Core Library of the North Dakota Geological Survey.These samples,spanning the entire thickness of the formation,were sectioned and polished at defined depth intervals for detailed analyses and precise measurements of key reservoir properties critical to geothermal assessment.Several parameters were analyzed to assess the geothermal viability of these wells,including formation temperature,temperature gradient,porosity,thermal conductivity,energy storage potential,and estimated power output via the Organic Rankine Cycle(ORC).The results demonstrate significant depth-dependent variations in thermal and petrophysical properties.Specifically,the depth range of 4000-4500 m is identified as a promising target for EGS stimulation since it is characterized by elevated temperatures,high thermal conductivity,favorable temperature gradients,and sufficient porosity-all essential properties for enhancing permeability through hydraulic fracturing.Furthermore,the calculated energy content and potential ORC power output at these depths indicate that effective geothermal energy extraction is technically feasible.This suggests a compelling opportunity to repurpose existing fossil energy infrastructure-such as abandoned oil wells-for renewable geothermal applications.Overall,the findings of this study underscore the potential of sedimentary formations for EGS development and contribute to advancing low-carbon,diversified energy solutions in alignment with national decarbonization goals.展开更多
Hydraulic fracturing then fluid circulation in enhanced geothermal system(EGS)reservoirs have been shown to induce seismicity remote from the stimulation-potentially generated by the distal projection of thermoporoela...Hydraulic fracturing then fluid circulation in enhanced geothermal system(EGS)reservoirs have been shown to induce seismicity remote from the stimulation-potentially generated by the distal projection of thermoporoelastic stresses.We explore this phenomenon by evaluating stress perturbations resulting from stimulation of a single stage of hydraulic fracturing that is followed by thermal depletion of a prismatic zone adjacent to the hydraulic fracture.We use Coulomb failure stress to assess the effect of resulting stress perturbations on instability on adjacent critically-stressed faults.Results show that hydraulic fracturing in a single stage is capable of creating stress perturbations at distances to 1000 m that reach 10^(-5)-10^(-4)MPa.At a closer distance,the magnitude of stress perturbations increases even further.The stress perturbation induced by temperature depletion could also reach 10^(-3)-10^(-2)MPa within 1000 m-much higher than that by hydraulic fracturing.Considering that a critical change in Coulomb failure stress for fault instability is 10^(-2)MPa,a single stage of hydraulic fracturing and thermal drawdown are capable of reactivating critically-stressed faults at distances within 200 m and 1000 m,respectively.These results have important implications for understanding the distribution and magnitudes of stress perturbations driven by thermoporoelastic effects and the associated seismicity during the simulation and early production of EGS reservoirs.展开更多
Accurate prediction of hydraulic fracture propagation is vital for Enhanced Geothermal System(EGS)design.We study the first hydraulic fracturing job at the GR1 well in the Gonghe Basin using field data,where the overa...Accurate prediction of hydraulic fracture propagation is vital for Enhanced Geothermal System(EGS)design.We study the first hydraulic fracturing job at the GR1 well in the Gonghe Basin using field data,where the overall direction of hydraulic fractures does not show a delineated shape parallel to the maximum principal stress orientation.A field-scale numerical model based on the distinct element method is set up to carry out a fully coupled hydromechanical simulation,with the explicit representation of natural fractures via the discrete fracture network(DFN)approach.The effects of injection parameters and in situ stress on hydraulic fracture patterns are then quantitatively assessed.The study reveals that shear-induced deformation primarily governs the fracturing morphology in the GR1 well,driven by smaller injection rates and viscosities that promote massive activation of natural fractures,ultimately dominating the direction of hydraulic fracturing.Furthermore,the increase of in situ differential stress may promote shear damage of natural fracture surfaces,with the exact influence pattern depending on the combination of specific discontinuity properties and in situ stress state.Finally,we provide recommendations for EGS fracturing based on the influence characteristics of multiple parameters.This study can serve as an effective basis and reference for the design and optimization of EGS in the Gonghe basin and other sites.展开更多
The optimization of working fluids in single-well coaxial geothermal systems presents a critical pathway for advancing the use of enhanced geothermal systems(EGS)in renewable energy applications.This study evaluates t...The optimization of working fluids in single-well coaxial geothermal systems presents a critical pathway for advancing the use of enhanced geothermal systems(EGS)in renewable energy applications.This study evaluates the thermo-hydraulic performance of three working fluids(H_(2)O,CO_(2),and H_(2))in a single-well coaxial geothermal system,focusing on the effects of their injection temperatures.Using a 3D finite element model in COMSOL Multiphysics,simulations were conducted at three injection temperatures(17℃,27℃,40℃)under constant mass flow rates.The results reveal that hydrogen significantly outperforms water and carbon dioxide,achieving a 297.77% and 5453.76% higher thermal output,respectively.Notably,the heat transfer efficiency is significantly improved when the injected working fluids are at 40℃,compared to 27℃;this demonstrates a positive correlation between injection temperature and thermal recovery.Though water systems exhibit better geological compatibility,the superior thermal properties of hydrogen position it as a promising alternative-despite potential subsurface challenges.This study provides critical insights for advancing the application of high-efficiency geothermal systems as well as the development of non-aqueous working fluids,thus contributing to the sustainable utilization of geothermal energy.展开更多
Large basins are currently the global focus for geothermal development,with their hydrothermal system being controlled by a variety of factors,such as basement relief and fracture development.Donglihu is located at th...Large basins are currently the global focus for geothermal development,with their hydrothermal system being controlled by a variety of factors,such as basement relief and fracture development.Donglihu is located at the north of the Cangxian uplift in the North China Basin,the concentrated geothermal resource development zone in North China.This study systematically collects temperature logging data and long-term dynamic monitoring of water level and water quality as well as group well tracer test data carried out in this area in recent years,on the basis of which the hydrothermal controlling role of the deep hidden faults is systematically analyzed.The results show that the Cangdong fault communicates with different geothermal reservoirs in the shallow part and plays a specific role in the water-heat channel of the local area.As a result,the high-value area of the geothermal temperature gradient in the sedimentary layer of the Donglihu area is distributed around the Cangdong fault.The geothermal reservoir temperature of the Minghuazhen Formation within the influence of the fault is also significantly higher than the regional average,the hydraulic head of different geothermal reservoirs showing a consistent and synergistic trend.However,the water quality has been stable for many years without any apparent changes.This understanding has a particular significance for further deepening understanding of the geothermal genesis mechanism in sedimentary basins and guiding future geothermal exploration and development in the Donglihu area.展开更多
The permeability contrast between the Hot Dry Rock(HDR)reservoir and the surrounding formations is a key factor governing fluid loss in Enhanced Geothermal Systems(EGS).This study thus aims to investigate its impact o...The permeability contrast between the Hot Dry Rock(HDR)reservoir and the surrounding formations is a key factor governing fluid loss in Enhanced Geothermal Systems(EGS).This study thus aims to investigate its impact on system performance under varying operating conditions,and a three-dimensional thermo–hydro–mechanical(THM)coupled EGS model is developed based on the geological parameters of the GR1 well in the Qiabuqia region.The coupled processes of fluid flow,heat transfer,and geomechanics within the reservoir under varying reservoir–surrounding rock permeability contrasts,as well as the flow and heat exchange along the wellbores fromthe reservoir to the surface are simulated.Then,the influence of permeability contrast,production pressure,injection rate,and injection temperature on fluid loss and heat extraction performance over a 35-year operation period is quantitatively assessed.Theresults show that increasing the permeability contrast effectively suppresses fluid loss and enhances early-stage heat production,but also accelerates thermal breakthrough and shortens the stable operation period.When the contrast rises from 1×10^(3) to 1×10^(5),the cumulative fluid loss rate drops from 54.34%to 0.23%,and the total heat production increases by 132%,although the breakthrough occurs 5 years earlier.Meanwhile,higher production pressure delays thermal breakthrough and slows transient temperature decline,but exacerbates fluid loss and reduces heat production power.For instance,raising the pressure from 17 to 21 MPa increases the fluid loss rate from 33.17%to 54.34%and reduces average annual heat production power from 25.43 to 14.59MWth.In addition,increasing the injection rate(46 to 66 kg/s)lowers fluid loss rate but brings forward thermal breakthrough by 9 years and causes a 41 K temperature drop at the end of operation.Notably,under high fluid loss,the dynamic response pattern of heat production power shifts from a temperature-dominated“stable–breakthrough–decline”mode to a novel“rising–breakthrough–decline”mode jointly governed by both production temperature and flow rates.These findings provide theoretical support and engineering guidance for improving EGS performance.展开更多
This study introduces a Transformer-based multimodal fusion framework for simulating multiphase flow and heat transfer in carbon dioxide(CO_(2))–water enhanced geothermal systems(EGS).The model integrates geological ...This study introduces a Transformer-based multimodal fusion framework for simulating multiphase flow and heat transfer in carbon dioxide(CO_(2))–water enhanced geothermal systems(EGS).The model integrates geological parameters,thermal gradients,and control schedules to enable fast and accurate prediction of complex reservoir dynamics.The main contributions are:(i)development of a workflow that couples physics-based reservoir simulation with a Transformer neural network architecture,(ii)design of physics-guided loss functions to enforce conservation of mass and energy,(iii)application of the surrogate model to closed-loop optimization using a differential evolution(DE)algorithm,and(iv)incorporation of economic performance metrics,such as net present value(NPV),into decision support.The proposed framework achieves root mean square error(RMSE)of 3–5%,mean absolute error(MAE)below 4%,and coefficients of determination greater than 0.95 across multiple prediction targets,including production rates,pressure distributions,and temperature fields.When compared with recurrent neural network(RNN)baselines such as gated recurrent units(GRU)and long short-term memory networks(LSTM),as well as a physics-informed reduced-order model,the Transformer-based approach demonstrates superior accuracy and computational efficiency.Optimization experiments further show a 15–20%improvement in NPV,highlighting the framework’s potential for real-time forecasting,optimization,and decision-making in geothermal reservoir engineering.展开更多
As mining activities expand deeper,deep high-temperature formations seriously threaten the future safe exploitation,while deep geothermal energy has great potential for development.Combining the formation cooling and ...As mining activities expand deeper,deep high-temperature formations seriously threaten the future safe exploitation,while deep geothermal energy has great potential for development.Combining the formation cooling and geothermal mining in mines to establish a thermos-hydraulic coupling numerical model for fractured formation.The study investigates the formation heat transfer behaviour,heat recovery performance and thermal economic benefits influenced during the life cycle.The results show that the accumulation of cold energy during the cold storage phase induces a decline in formation temperature.The heat recovery phase is determined by the extent of the initial cold domain,which contracts inward from the edge and decelerates the heat recovery rate gradually.With groundwater velocity increases,the thermal regulation efficiency gradually increases,the production temperature decreases,while the effective radius and thermal power increase first and then decrease.The injected volume and temperature significantly affect,with higher injection temperatures slowing thermal recovery,and the thermal regulation efficiency is more sensitive to changes in formation permeability and thermal conductivity.The heat extraction performance is positively correlated with all factors.The levelized cost of electricity is estimated at 0.1203$/(kW·h)during the cold storage.During the heat recovery,annual profit is primarily driven by cooling benefits.展开更多
This paper provides an overview of conventional geothermal systems and unconventional geothermal developments as a common reference is needed for discussions between energy professionals. Conventional geothermal syste...This paper provides an overview of conventional geothermal systems and unconventional geothermal developments as a common reference is needed for discussions between energy professionals. Conventional geothermal systems have the heat, permeability and fluid, requiring only drilling down to °C, normal heat flow or decaying radiogenic granite as heat sources, and used in district heating. Medium-temperature (MT) 100°C - 190°C, and high-temperature (HT) 190°C - 374°C resources are mostly at plate boundaries, with volcanic intrusive heat source, used mostly for electricity generation. Single well capacities are °C - 500°C) and a range of depths (1 m to 20 Km), but lack permeability or fluid, thus requiring stimulations for heat extraction by conduction. HVAC is 1 - 2 m deep and shallow geothermal down to 500 m in wells, both capturing °C, with °C are either advanced by geothermal developers at <7 Km depth (Enhanced Geothermal Systems (EGS), drilling below brittle-ductile transition zones and under geothermal fields), or by the Oil & Gas industry (Advanced Geothermal Systems, heat recovery from hydrocarbon wells or reservoirs, Superhot Rock Geothermal, and millimeter-wave drilling down to 20 Km). Their primary aim is electricity generation, relying on closed-loops, but EGS uses fractures for heat exchange with earthquake risks during fracking. Unconventional approaches could be everywhere, with shallow geothermal already functional. The deeper and hotter unconventional alternatives are still experimental, overcoming costs and technological challenges to become fully commercial. Meanwhile, the conventional geothermal resources remain the most proven opportunities for investments and development.展开更多
It is common sense that a deeper well implies higher temperature in the exploration of deep geothermal resources, especially with hot dry rock(HDR) geothermal resources, which are generally exploited in terms of enhan...It is common sense that a deeper well implies higher temperature in the exploration of deep geothermal resources, especially with hot dry rock(HDR) geothermal resources, which are generally exploited in terms of enhanced geothermal systems(EGS). However, temperature is always different even at the same depth in the upper crust due to different heat sources. This paper summarizes the heat sources and classifies them into two types and five sub-types: crustorigin(partial melting, non-magma-generated tectonic events and radiogenic heat production), and mantle-origin(magma and heat conducted from the mantle). A review of global EGS sites is presented related to the five sub-types of heat sources. According to our new catalog, 71% of EGS sites host mantle-origin heat sources. The temperature logging curves indicate that EGS sites which host mantle-origin magma heat sources have the highest temperature. Therefore, high heat flow(>100 m W/m^(2)) regions with mantle-origin magma heat sources should be highlighted for the future exploration of EGS. The principle to identify the heat source is elucidated by applying geophysical and geochemical methods including noble gas isotope geochemistry and lithospheric thermal structure analysis. This analytical work will be helpful for the future exploration and assessment of HDR geothermal resources.展开更多
In geothermal systems, the temperature distribution of heat flow in the wellbore is dependent on the well structure and the geological conditions of the surrounding formation. Understanding of heat transfer in the tub...In geothermal systems, the temperature distribution of heat flow in the wellbore is dependent on the well structure and the geological conditions of the surrounding formation. Understanding of heat transfer in the tubing-casing annulus can reduce the heat losses of wellbore fluid during the production process. The present study discusses the possible means of heat transfer in the annulus, and develops a piecewise equation for estimating the convective heat transfer coefficient with a wider valid condition of 0〈Ra〈7.17×10^8. By converting the radiation and natural convection into equivalent thermal conduction, their sum is defined as a total thermal conductivity to describe the heat transfer in the annulus. The results indicate that the annulus filled with gas can be utilized as a good thermal barrier for the fluid in the wellbore. Additionally, the contribution of radiation will increase to occupy a majority proportion in the total thermal conductivity when the annular size increases and the materials have high emissivity. Otherwise, thermal radiation is just the second factor.展开更多
The Enhanced Geothermal System(EGS) is an artificial geothermal system that aims to economically extract heat from hot dry rock(HDR) through the creation of an artificial geothermal reservoir. Chemical stimulation is ...The Enhanced Geothermal System(EGS) is an artificial geothermal system that aims to economically extract heat from hot dry rock(HDR) through the creation of an artificial geothermal reservoir. Chemical stimulation is thought to be an effective method to create fracture networks and open existing fractures in hot dry rocks by injecting chemical agents into the reservoir to dissolve the minerals. Granite is a common type of hot dry rock. In this paper, a series of chemical stimulation experiments were implemented using acid and alkaline agents under high temperature and pressure conditions that mimic the environment of formation. Granite rock samples used in the experiments are collected from the potential EGS reservoir in the Matouying area, Hebei, China. Laboratory experimental results show that the corrosion ratio per unit area of rock is 3.2% in static acid chemical experiments and 0.51% in static alkaline chemical experiments. The permeability of the core is increased by 1.62 times in dynamic acid chemical experiments and 2.45 times in dynamic alkaline chemical experiments. A scanning electron microscope analysis of the core illustrates that secondary minerals, such as chlorite, spherical silica, and montmorillonite, were formed, due to acid-rock interaction with plagioclase being precipitated by alkaline-rock interactions. Masking agents in alkaline chemical agents can slightly reduce the degree of plagioclase formation. A chemical simulation model was built using TOUGHREACT, the mineral dissolution and associated ion concentration variation being reproduced by this reactive transport model.展开更多
In this study,Shengli fault depression,Tangyuan fault basin,and northern Songliao Basin in Yitong‒Yilan fault zone of Heilongjiang province are considered the research areas for geothermal anomaly.Based on the tempera...In this study,Shengli fault depression,Tangyuan fault basin,and northern Songliao Basin in Yitong‒Yilan fault zone of Heilongjiang province are considered the research areas for geothermal anomaly.Based on the temperature of the deep thermal reservoir,the hydrothermal fl uid channel,caprock thickness,and the mode of heat transfer,which are the main factors controlling the geothermal reservoir formation,we examined geothermal resource system of the underground HDR in this area.First,we inversed the aeromagnetic data,calculated the Curie isotherm depth,analyzed the geothermal distribution characteristics,and estimated the temperature of the deep heat source.Second,we applied the controlled source audio frequency magnetotelluric(CSAMT)and magnetotelluric(MT)methods to obtain the deep electrical structure of the study area.We determined the thickness of the caprock and the hydrothermal fluid channel.Finally,we obtained the borehole geothermal steady-state temperature measurement data and water sample chemical analysis data from the logging temperature curves of 24 wells to infer the mode of heat transfer.Based on the results,we built a model of the geothermal system of the sedimentary basin in this area.The results show that the depth of Curie isotherm in the study area is 17–39 km.The resistivity of sedimentary caprock in the north of Songliao basin is low,and there exists a deep heat source,which is mainly thermal convection.In contrast,in Shengli and Tangyuan fault basins,heat conduction is dominant.Based on the geothermal system model,we conclude that the area from Daqing to Lindian in Songliao basin has a thermal-convection-dominated sedimentary basin geothermal system.Heat exchange is realized by the upwelling of mantle-derived thermal materials through fracture channels.The thick sedimentary caprock reduces the heat loss.It can be a target for sustainable development and utilization of HDR.展开更多
The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs...The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs in the bottom of borehole for geothermal exploration, and the convective hot springs in the basin-edge uplift fracture are in zonal distribution and with high-temperature geothermal water. There are still some divergences about the heat source mechanism of the basin. In this paper, queries to the view of mantle-derived heat source have been put forward, coming up with geochemical evidences to prove that the radiogenic heat of granite is the heat source within the mantle. Additionally, temperature curve is drawn based on the geothermal boring and geochemical geothermometer has been adopted for an estimation of the temperature and depth of the geothermal reservoir, it has been found that the surrounding mountains belong to the medium-temperature geothermal system while the area within the basin belongs to the high-temperature geothermal system with the temperature of borehole bottom reaching up to 175-180 ℃. In this paper, discussions on the problems existing in the calculation of geothermal gradient and the differences generated by the geothermal system have been carried out.展开更多
In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)...In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical(THM)coupling processes for heat extraction in geothermal reservoir.We further employed the model on the Habanero enhanced geothermal systems(EGS)project located in Australia.First,our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations,as well as uneven spatial distribution of shear failure in 3D fracture networks.Activated shear failure is mainly concentrated in the first fracture cluster.Secondly,channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal stresses.Moreover,the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and temperature.The NR-DFN model framework and the Habanero EGS's results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.展开更多
Enhanced geothermal system(EGS)is a primary method to develop geothermal resources stored in hot dry rock(HDR),but it faces several key problems,such as unreasonable hydraulic fracture networks at high reservoir tempe...Enhanced geothermal system(EGS)is a primary method to develop geothermal resources stored in hot dry rock(HDR),but it faces several key problems,such as unreasonable hydraulic fracture networks at high reservoir temperature,unclear multi-scale and multi-field coupling regularity,low heat extraction efficiency caused by the flashing flow in geothermal wells,and low thermoelectric conversion efficiency of geothermal fluid,which restricts the large-scale commercial development of geothermal resources.To resolve these major bottleneck problems,systematically reviews and analysis of the research progress and development trend of EGS are conducted in this paper.Particular attentions are devoted to four key technologies involved in the development of HDR geothermal resource by EGS:(1)the hydraulic fracturing technology for HDR reservoirs,including reservoir reconstruction methods,hydraulic fracturing network forming mechanisms and fracture propagation prediction models is illustrated in detail;(2)the fracture characterization methods,mathematical models and solution methods are described from three aspects including pore-scale multi-field coupled models,reservoir-scale multi-field coupled models and upscaling methods;(3)the efficient extraction technology of wellbore thermal fluid,involving the mechanism of flashing flows in geothermal wells and the experimental and numerical methods for investigating the characteristics offlashing flows are discussed;(4)the HDR geothermal power generation technologies,considering the principles of geothermal power generation,the types of power generation systems and the main application markets are introduced.In conclusion,EGS is a technology-intensive system,however,due to the complex working conditions of the underground reservoirs and the instability of the ground equipment,theoretical research tends to be separated from the practice.For the purpose of promoting the applicability of EGS,intimate combination and mutual guidance with the pilot tests are necessary to develop a production-research combined mode,and to raise the awareness and break through the key points in a constant back-and-forth.展开更多
As a potentially viable renewable energy, Enhanced Geothermal Systems(EGSs) extract heat from hot dry rock(HDR) reservoirs to produce electricity and heat, which promotes the progress towards carbon peaking and carbon...As a potentially viable renewable energy, Enhanced Geothermal Systems(EGSs) extract heat from hot dry rock(HDR) reservoirs to produce electricity and heat, which promotes the progress towards carbon peaking and carbon neutralization. The main challenge for EGSs is to reduce the investment cost. In the present study, thermo-economic investigations of EGS projects are conducted. The effects of geofluid mass flow rate, wellhead temperature and loss rate on the thermo-economic performance of the EGS organic Rankine cycle(ORC) are studied. A performance comparison between EGS-ORC and the EGS combined heating and power system(CHP) is presented. Considering the CO_(2)emission reduction benefits, the influence of carbon emission trading price on the levelized cost of energy(LCOE) is also presented. It is indicated that the geofluid mass flow rate is a critical parameter in dictating the success of a project. Under the assumed typical working conditions, the LCOE of EGS-ORC and EGS-CHP systems are 24.72 and 16.1 cents/k Wh, respectively. Compared with the EGS-ORC system, the LCOE of the EGS-CHP system is reduced by 35%. EGS-CHP systems have the potential to be economically viable in the future. With carbon emission trading prices of 12.76 USD/ton, the LCOE can be reduced by approximately 8.5%.展开更多
Geothermal energy from deep underground (or geological) formations,with or without its combination with carbon capture and storage (CCS),can be a key technology to mitigate anthropogenic greenhouse gas emissions and m...Geothermal energy from deep underground (or geological) formations,with or without its combination with carbon capture and storage (CCS),can be a key technology to mitigate anthropogenic greenhouse gas emissions and meet the 2050 net‐zero carbon emission target.Geothermal resources in low‐permeability and medium‐and high‐temperature reservoirs in sedimentary sequence require hydraulic stimulation for enhanced geothermal systems (EGS).However,fluid migration for geothermal energy in EGS or with potential CO_(2) storage in a CO_(2)‐EGS are both dependent on the in situ flow pathway network created by induced fluid injection.These thermo‐mechanical interactions can be complex and induce varying alterations in the mechanical response when the working fluid is water (in EGS) or supercritical CO_(2)(in CO_(2)‐EGS),which could impact the geothermal energy recovery from geological formations.Therefore,there is a need for a deeper understanding of the heat extraction process in EGS and CO_(2)‐EGS.This study presents a systematic review of the effects of changes in mechanical properties and behavior of deep underground rocks on the induced flow pathway and heat recovery in EGS reservoirs with or without CO_(2) storage in CO_(2) ‐EGS.Further,we proposed waterless‐stimulated EGS as an alternative approach to improve heat energy extraction in EGS.Lastly,based on the results of our literature review and proposed ideas,we recommend promising areas of investigation that may provide more insights into understanding geothermo‐mechanics to further stimulate new research studies and accelerate the development of geothermal energy as a viable clean energy technology.展开更多
Post shut‐in seismic events in enhanced geothermal systems(EGSs)occur predominantly at the outer rim of the co‐injection seismic cloud.The concept of postinjection fracture and fault closure near the injection well ...Post shut‐in seismic events in enhanced geothermal systems(EGSs)occur predominantly at the outer rim of the co‐injection seismic cloud.The concept of postinjection fracture and fault closure near the injection well has been proposed and validated as a mechanism for enhancing post shut‐in pressure diffusion that promotes seismic hazard.This phenomenon is primarily attributed to the poro‐elastic closure of fractures resulting from the reduction of wellbore pressure after injection termination.However,the thermal effects in EGSs,mainly including heat transfer and thermal stress,may not be trivial and their role in postinjection fault closure and pressure evolution needs to be explored.In this study,we performed numerical simulations to analyze the relative importance of poro‐elasticity,heat transfer,and thermo‐elasticity in promoting postinjection fault closure and pressure diffusion.The numerical model wasfirst validated against analytical solutions in terms offluid pressure diffusion and against heatedflow‐through experiments in terms of thermal processes.We then quantified and distinguished the contribution of each individual mechanism by comparing four different shut‐in scenarios simulated under different coupled conditions.Our results highlight the importance of poro‐elastic fault closure in promoting postinjection pressure buildup and seismicity,and suggest that heat transfer can further augment the fault closure‐induced pressure increase and thus potentially intensify the postinjection seismic hazard,with minimal contribution from thermo‐elasticity.展开更多
With the development of industrial activities,global warming has accelerated due to excessive emission of CO_(2).Enhanced Geothermal System(EGS)utilizes deep geothermal heat for power generation.Although porous medium...With the development of industrial activities,global warming has accelerated due to excessive emission of CO_(2).Enhanced Geothermal System(EGS)utilizes deep geothermal heat for power generation.Although porous medium theory is commonly employed to model geothermal reservoirs in EGS,Hot Dry Rock(HDR)presents a challenge as it consists of impermeable granite with zero porosity,potentially distorting the physical interpretation.To address this,the Lattice Boltzmann Method(LBM)is employed to simulate CO_(2)flow within geothermal reservoirs and the Finite Volume Method(FVM)to solve the energy conservation equation for temperature distribution.This combined method of LBM and FVM is imple-mented using MATLAB.The results showed that the Reynolds numbers(Re)of 3,000 and 8,000 lead to higher heat extraction rates from geothermal reservoirs.However,higher Re values may accelerate thermal breakthrough,posing challenges to EGS operation.Meanwhile,non-equilibrium of density in fractures becomes more pronounced during the system's life cycle,with non-Darcy's law becoming significant at Re values of 3,000 and 8,000.Density stratification due to buoyancy effects significantly impacts temperature distribution within geothermal reservoirs,with buoyancy effects at Re=100 under gravitational influence being noteworthy.Larger Re values(3,000 and 8,000)induce stronger forced convection,leading to more uniform density distribution.The addition of proppant negatively affects heat transfer performance in geothermal reservoirs,especially in single fractures.Practical engineering considerations should determine the quantity of proppant through detailed numerical simulations.展开更多
文摘An enhanced geothermal system(EGS)represents a promising approach to sustainable energy generation by harnessing subsurface heat from deep geological formations with low natural permeability.Sedimentary basins-such as the Williston Basin in North Dakota-are considered viable candidates for EGS development due to their broad geographic extent and moderate geothermal potential.Notably,depleted or non-productive oil wells within these basins offer a cost-effective opportunity for EGS implementation as they can be repurposed,thereby significantly reducing the need for new drilling.This study evaluates the feasibility of EGS deployment in McKenzie County,North Dakota.Core samples from five partially abandoned or dry oil wells associated with production from the Red River Formation were obtained from the Core Library of the North Dakota Geological Survey.These samples,spanning the entire thickness of the formation,were sectioned and polished at defined depth intervals for detailed analyses and precise measurements of key reservoir properties critical to geothermal assessment.Several parameters were analyzed to assess the geothermal viability of these wells,including formation temperature,temperature gradient,porosity,thermal conductivity,energy storage potential,and estimated power output via the Organic Rankine Cycle(ORC).The results demonstrate significant depth-dependent variations in thermal and petrophysical properties.Specifically,the depth range of 4000-4500 m is identified as a promising target for EGS stimulation since it is characterized by elevated temperatures,high thermal conductivity,favorable temperature gradients,and sufficient porosity-all essential properties for enhancing permeability through hydraulic fracturing.Furthermore,the calculated energy content and potential ORC power output at these depths indicate that effective geothermal energy extraction is technically feasible.This suggests a compelling opportunity to repurpose existing fossil energy infrastructure-such as abandoned oil wells-for renewable geothermal applications.Overall,the findings of this study underscore the potential of sedimentary formations for EGS development and contribute to advancing low-carbon,diversified energy solutions in alignment with national decarbonization goals.
基金funded by the National Natural Science Foundation of China(Grant Nos.42107163 and 42320104003)support from the G.Albert Shoemaker endowment.
文摘Hydraulic fracturing then fluid circulation in enhanced geothermal system(EGS)reservoirs have been shown to induce seismicity remote from the stimulation-potentially generated by the distal projection of thermoporoelastic stresses.We explore this phenomenon by evaluating stress perturbations resulting from stimulation of a single stage of hydraulic fracturing that is followed by thermal depletion of a prismatic zone adjacent to the hydraulic fracture.We use Coulomb failure stress to assess the effect of resulting stress perturbations on instability on adjacent critically-stressed faults.Results show that hydraulic fracturing in a single stage is capable of creating stress perturbations at distances to 1000 m that reach 10^(-5)-10^(-4)MPa.At a closer distance,the magnitude of stress perturbations increases even further.The stress perturbation induced by temperature depletion could also reach 10^(-3)-10^(-2)MPa within 1000 m-much higher than that by hydraulic fracturing.Considering that a critical change in Coulomb failure stress for fault instability is 10^(-2)MPa,a single stage of hydraulic fracturing and thermal drawdown are capable of reactivating critically-stressed faults at distances within 200 m and 1000 m,respectively.These results have important implications for understanding the distribution and magnitudes of stress perturbations driven by thermoporoelastic effects and the associated seismicity during the simulation and early production of EGS reservoirs.
基金support from the National Natural Science Foundation of China(Grant Nos.42320104003,42177175,and 42077247)the Fundamental Research Funds for the Central Universities.
文摘Accurate prediction of hydraulic fracture propagation is vital for Enhanced Geothermal System(EGS)design.We study the first hydraulic fracturing job at the GR1 well in the Gonghe Basin using field data,where the overall direction of hydraulic fractures does not show a delineated shape parallel to the maximum principal stress orientation.A field-scale numerical model based on the distinct element method is set up to carry out a fully coupled hydromechanical simulation,with the explicit representation of natural fractures via the discrete fracture network(DFN)approach.The effects of injection parameters and in situ stress on hydraulic fracture patterns are then quantitatively assessed.The study reveals that shear-induced deformation primarily governs the fracturing morphology in the GR1 well,driven by smaller injection rates and viscosities that promote massive activation of natural fractures,ultimately dominating the direction of hydraulic fracturing.Furthermore,the increase of in situ differential stress may promote shear damage of natural fracture surfaces,with the exact influence pattern depending on the combination of specific discontinuity properties and in situ stress state.Finally,we provide recommendations for EGS fracturing based on the influence characteristics of multiple parameters.This study can serve as an effective basis and reference for the design and optimization of EGS in the Gonghe basin and other sites.
基金funded by the China National Administration of Coal Geology Science and Technology Innovation Project"Research on Clean Energy Exploration and Development Technology"(ZMKJ-2021-ZX04)the China National Administration of Coal Geology Special Task Project"Research on Geothermal Resource Exploration and Development Technology"(ZMKJ-2023-JBGS06)。
文摘The optimization of working fluids in single-well coaxial geothermal systems presents a critical pathway for advancing the use of enhanced geothermal systems(EGS)in renewable energy applications.This study evaluates the thermo-hydraulic performance of three working fluids(H_(2)O,CO_(2),and H_(2))in a single-well coaxial geothermal system,focusing on the effects of their injection temperatures.Using a 3D finite element model in COMSOL Multiphysics,simulations were conducted at three injection temperatures(17℃,27℃,40℃)under constant mass flow rates.The results reveal that hydrogen significantly outperforms water and carbon dioxide,achieving a 297.77% and 5453.76% higher thermal output,respectively.Notably,the heat transfer efficiency is significantly improved when the injected working fluids are at 40℃,compared to 27℃;this demonstrates a positive correlation between injection temperature and thermal recovery.Though water systems exhibit better geological compatibility,the superior thermal properties of hydrogen position it as a promising alternative-despite potential subsurface challenges.This study provides critical insights for advancing the application of high-efficiency geothermal systems as well as the development of non-aqueous working fluids,thus contributing to the sustainable utilization of geothermal energy.
基金funded by Public Interest Monitoring Project(No.XCSD-2024-317)of the Tianjin Municipal Bureau of Planning and Natural Resources。
文摘Large basins are currently the global focus for geothermal development,with their hydrothermal system being controlled by a variety of factors,such as basement relief and fracture development.Donglihu is located at the north of the Cangxian uplift in the North China Basin,the concentrated geothermal resource development zone in North China.This study systematically collects temperature logging data and long-term dynamic monitoring of water level and water quality as well as group well tracer test data carried out in this area in recent years,on the basis of which the hydrothermal controlling role of the deep hidden faults is systematically analyzed.The results show that the Cangdong fault communicates with different geothermal reservoirs in the shallow part and plays a specific role in the water-heat channel of the local area.As a result,the high-value area of the geothermal temperature gradient in the sedimentary layer of the Donglihu area is distributed around the Cangdong fault.The geothermal reservoir temperature of the Minghuazhen Formation within the influence of the fault is also significantly higher than the regional average,the hydraulic head of different geothermal reservoirs showing a consistent and synergistic trend.However,the water quality has been stable for many years without any apparent changes.This understanding has a particular significance for further deepening understanding of the geothermal genesis mechanism in sedimentary basins and guiding future geothermal exploration and development in the Donglihu area.
基金supported by the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation(GZC20251944)the National Natural Science Foundation of China(No.52376044)the National Key Research and Development Program of China(2024YFE0100800).
文摘The permeability contrast between the Hot Dry Rock(HDR)reservoir and the surrounding formations is a key factor governing fluid loss in Enhanced Geothermal Systems(EGS).This study thus aims to investigate its impact on system performance under varying operating conditions,and a three-dimensional thermo–hydro–mechanical(THM)coupled EGS model is developed based on the geological parameters of the GR1 well in the Qiabuqia region.The coupled processes of fluid flow,heat transfer,and geomechanics within the reservoir under varying reservoir–surrounding rock permeability contrasts,as well as the flow and heat exchange along the wellbores fromthe reservoir to the surface are simulated.Then,the influence of permeability contrast,production pressure,injection rate,and injection temperature on fluid loss and heat extraction performance over a 35-year operation period is quantitatively assessed.Theresults show that increasing the permeability contrast effectively suppresses fluid loss and enhances early-stage heat production,but also accelerates thermal breakthrough and shortens the stable operation period.When the contrast rises from 1×10^(3) to 1×10^(5),the cumulative fluid loss rate drops from 54.34%to 0.23%,and the total heat production increases by 132%,although the breakthrough occurs 5 years earlier.Meanwhile,higher production pressure delays thermal breakthrough and slows transient temperature decline,but exacerbates fluid loss and reduces heat production power.For instance,raising the pressure from 17 to 21 MPa increases the fluid loss rate from 33.17%to 54.34%and reduces average annual heat production power from 25.43 to 14.59MWth.In addition,increasing the injection rate(46 to 66 kg/s)lowers fluid loss rate but brings forward thermal breakthrough by 9 years and causes a 41 K temperature drop at the end of operation.Notably,under high fluid loss,the dynamic response pattern of heat production power shifts from a temperature-dominated“stable–breakthrough–decline”mode to a novel“rising–breakthrough–decline”mode jointly governed by both production temperature and flow rates.These findings provide theoretical support and engineering guidance for improving EGS performance.
文摘This study introduces a Transformer-based multimodal fusion framework for simulating multiphase flow and heat transfer in carbon dioxide(CO_(2))–water enhanced geothermal systems(EGS).The model integrates geological parameters,thermal gradients,and control schedules to enable fast and accurate prediction of complex reservoir dynamics.The main contributions are:(i)development of a workflow that couples physics-based reservoir simulation with a Transformer neural network architecture,(ii)design of physics-guided loss functions to enforce conservation of mass and energy,(iii)application of the surrogate model to closed-loop optimization using a differential evolution(DE)algorithm,and(iv)incorporation of economic performance metrics,such as net present value(NPV),into decision support.The proposed framework achieves root mean square error(RMSE)of 3–5%,mean absolute error(MAE)below 4%,and coefficients of determination greater than 0.95 across multiple prediction targets,including production rates,pressure distributions,and temperature fields.When compared with recurrent neural network(RNN)baselines such as gated recurrent units(GRU)and long short-term memory networks(LSTM),as well as a physics-informed reduced-order model,the Transformer-based approach demonstrates superior accuracy and computational efficiency.Optimization experiments further show a 15–20%improvement in NPV,highlighting the framework’s potential for real-time forecasting,optimization,and decision-making in geothermal reservoir engineering.
基金financial support from the National Natural Science Foundation of China(Nos.52434006,52374151,and 51927808)。
文摘As mining activities expand deeper,deep high-temperature formations seriously threaten the future safe exploitation,while deep geothermal energy has great potential for development.Combining the formation cooling and geothermal mining in mines to establish a thermos-hydraulic coupling numerical model for fractured formation.The study investigates the formation heat transfer behaviour,heat recovery performance and thermal economic benefits influenced during the life cycle.The results show that the accumulation of cold energy during the cold storage phase induces a decline in formation temperature.The heat recovery phase is determined by the extent of the initial cold domain,which contracts inward from the edge and decelerates the heat recovery rate gradually.With groundwater velocity increases,the thermal regulation efficiency gradually increases,the production temperature decreases,while the effective radius and thermal power increase first and then decrease.The injected volume and temperature significantly affect,with higher injection temperatures slowing thermal recovery,and the thermal regulation efficiency is more sensitive to changes in formation permeability and thermal conductivity.The heat extraction performance is positively correlated with all factors.The levelized cost of electricity is estimated at 0.1203$/(kW·h)during the cold storage.During the heat recovery,annual profit is primarily driven by cooling benefits.
文摘This paper provides an overview of conventional geothermal systems and unconventional geothermal developments as a common reference is needed for discussions between energy professionals. Conventional geothermal systems have the heat, permeability and fluid, requiring only drilling down to °C, normal heat flow or decaying radiogenic granite as heat sources, and used in district heating. Medium-temperature (MT) 100°C - 190°C, and high-temperature (HT) 190°C - 374°C resources are mostly at plate boundaries, with volcanic intrusive heat source, used mostly for electricity generation. Single well capacities are °C - 500°C) and a range of depths (1 m to 20 Km), but lack permeability or fluid, thus requiring stimulations for heat extraction by conduction. HVAC is 1 - 2 m deep and shallow geothermal down to 500 m in wells, both capturing °C, with °C are either advanced by geothermal developers at <7 Km depth (Enhanced Geothermal Systems (EGS), drilling below brittle-ductile transition zones and under geothermal fields), or by the Oil & Gas industry (Advanced Geothermal Systems, heat recovery from hydrocarbon wells or reservoirs, Superhot Rock Geothermal, and millimeter-wave drilling down to 20 Km). Their primary aim is electricity generation, relying on closed-loops, but EGS uses fractures for heat exchange with earthquake risks during fracking. Unconventional approaches could be everywhere, with shallow geothermal already functional. The deeper and hotter unconventional alternatives are still experimental, overcoming costs and technological challenges to become fully commercial. Meanwhile, the conventional geothermal resources remain the most proven opportunities for investments and development.
基金supported by the National Key Research and Development Program of China(Grant No.2018YFB1501801)the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2020067)。
文摘It is common sense that a deeper well implies higher temperature in the exploration of deep geothermal resources, especially with hot dry rock(HDR) geothermal resources, which are generally exploited in terms of enhanced geothermal systems(EGS). However, temperature is always different even at the same depth in the upper crust due to different heat sources. This paper summarizes the heat sources and classifies them into two types and five sub-types: crustorigin(partial melting, non-magma-generated tectonic events and radiogenic heat production), and mantle-origin(magma and heat conducted from the mantle). A review of global EGS sites is presented related to the five sub-types of heat sources. According to our new catalog, 71% of EGS sites host mantle-origin heat sources. The temperature logging curves indicate that EGS sites which host mantle-origin magma heat sources have the highest temperature. Therefore, high heat flow(>100 m W/m^(2)) regions with mantle-origin magma heat sources should be highlighted for the future exploration of EGS. The principle to identify the heat source is elucidated by applying geophysical and geochemical methods including noble gas isotope geochemistry and lithospheric thermal structure analysis. This analytical work will be helpful for the future exploration and assessment of HDR geothermal resources.
文摘In geothermal systems, the temperature distribution of heat flow in the wellbore is dependent on the well structure and the geological conditions of the surrounding formation. Understanding of heat transfer in the tubing-casing annulus can reduce the heat losses of wellbore fluid during the production process. The present study discusses the possible means of heat transfer in the annulus, and develops a piecewise equation for estimating the convective heat transfer coefficient with a wider valid condition of 0〈Ra〈7.17×10^8. By converting the radiation and natural convection into equivalent thermal conduction, their sum is defined as a total thermal conductivity to describe the heat transfer in the annulus. The results indicate that the annulus filled with gas can be utilized as a good thermal barrier for the fluid in the wellbore. Additionally, the contribution of radiation will increase to occupy a majority proportion in the total thermal conductivity when the annular size increases and the materials have high emissivity. Otherwise, thermal radiation is just the second factor.
基金jointly supported by the National Key R&D Program of China(No.2018YFB1501802)the National Natural Science Foundation of China(No.41902309)funded by the Engineering Research Center of Geothermal Resources Development Technology and Equipment,Ministry of Education,Jilin University。
文摘The Enhanced Geothermal System(EGS) is an artificial geothermal system that aims to economically extract heat from hot dry rock(HDR) through the creation of an artificial geothermal reservoir. Chemical stimulation is thought to be an effective method to create fracture networks and open existing fractures in hot dry rocks by injecting chemical agents into the reservoir to dissolve the minerals. Granite is a common type of hot dry rock. In this paper, a series of chemical stimulation experiments were implemented using acid and alkaline agents under high temperature and pressure conditions that mimic the environment of formation. Granite rock samples used in the experiments are collected from the potential EGS reservoir in the Matouying area, Hebei, China. Laboratory experimental results show that the corrosion ratio per unit area of rock is 3.2% in static acid chemical experiments and 0.51% in static alkaline chemical experiments. The permeability of the core is increased by 1.62 times in dynamic acid chemical experiments and 2.45 times in dynamic alkaline chemical experiments. A scanning electron microscope analysis of the core illustrates that secondary minerals, such as chlorite, spherical silica, and montmorillonite, were formed, due to acid-rock interaction with plagioclase being precipitated by alkaline-rock interactions. Masking agents in alkaline chemical agents can slightly reduce the degree of plagioclase formation. A chemical simulation model was built using TOUGHREACT, the mineral dissolution and associated ion concentration variation being reproduced by this reactive transport model.
基金the State Key Research and Development Plan.Comprehensive Airborne Geophysics Exploration System Integration and Technical Demonstration(No.2017YFC0602201)。
文摘In this study,Shengli fault depression,Tangyuan fault basin,and northern Songliao Basin in Yitong‒Yilan fault zone of Heilongjiang province are considered the research areas for geothermal anomaly.Based on the temperature of the deep thermal reservoir,the hydrothermal fl uid channel,caprock thickness,and the mode of heat transfer,which are the main factors controlling the geothermal reservoir formation,we examined geothermal resource system of the underground HDR in this area.First,we inversed the aeromagnetic data,calculated the Curie isotherm depth,analyzed the geothermal distribution characteristics,and estimated the temperature of the deep heat source.Second,we applied the controlled source audio frequency magnetotelluric(CSAMT)and magnetotelluric(MT)methods to obtain the deep electrical structure of the study area.We determined the thickness of the caprock and the hydrothermal fluid channel.Finally,we obtained the borehole geothermal steady-state temperature measurement data and water sample chemical analysis data from the logging temperature curves of 24 wells to infer the mode of heat transfer.Based on the results,we built a model of the geothermal system of the sedimentary basin in this area.The results show that the depth of Curie isotherm in the study area is 17–39 km.The resistivity of sedimentary caprock in the north of Songliao basin is low,and there exists a deep heat source,which is mainly thermal convection.In contrast,in Shengli and Tangyuan fault basins,heat conduction is dominant.Based on the geothermal system model,we conclude that the area from Daqing to Lindian in Songliao basin has a thermal-convection-dominated sedimentary basin geothermal system.Heat exchange is realized by the upwelling of mantle-derived thermal materials through fracture channels.The thick sedimentary caprock reduces the heat loss.It can be a target for sustainable development and utilization of HDR.
文摘The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs in the bottom of borehole for geothermal exploration, and the convective hot springs in the basin-edge uplift fracture are in zonal distribution and with high-temperature geothermal water. There are still some divergences about the heat source mechanism of the basin. In this paper, queries to the view of mantle-derived heat source have been put forward, coming up with geochemical evidences to prove that the radiogenic heat of granite is the heat source within the mantle. Additionally, temperature curve is drawn based on the geothermal boring and geochemical geothermometer has been adopted for an estimation of the temperature and depth of the geothermal reservoir, it has been found that the surrounding mountains belong to the medium-temperature geothermal system while the area within the basin belongs to the high-temperature geothermal system with the temperature of borehole bottom reaching up to 175-180 ℃. In this paper, discussions on the problems existing in the calculation of geothermal gradient and the differences generated by the geothermal system have been carried out.
基金funded by the National Natural Science Foundation of China (No.U22A20166)Science and Technology Foundation of Guizhou Province (No.QKHJC-ZK[2023]YB074)+2 种基金Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical EngineeringInstitute of Rock and Soil MechanicsChinese Academy of Sciences (No.SKLGME022009)。
文摘In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical(THM)coupling processes for heat extraction in geothermal reservoir.We further employed the model on the Habanero enhanced geothermal systems(EGS)project located in Australia.First,our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations,as well as uneven spatial distribution of shear failure in 3D fracture networks.Activated shear failure is mainly concentrated in the first fracture cluster.Secondly,channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal stresses.Moreover,the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and temperature.The NR-DFN model framework and the Habanero EGS's results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.
基金supported by the Key Program of National Natural Science Foundation of China“Thermo-fluid-mechanical-chemical coupling research on heat-mass transport mechanism of enhanced geothermal system”(No.51936001).
文摘Enhanced geothermal system(EGS)is a primary method to develop geothermal resources stored in hot dry rock(HDR),but it faces several key problems,such as unreasonable hydraulic fracture networks at high reservoir temperature,unclear multi-scale and multi-field coupling regularity,low heat extraction efficiency caused by the flashing flow in geothermal wells,and low thermoelectric conversion efficiency of geothermal fluid,which restricts the large-scale commercial development of geothermal resources.To resolve these major bottleneck problems,systematically reviews and analysis of the research progress and development trend of EGS are conducted in this paper.Particular attentions are devoted to four key technologies involved in the development of HDR geothermal resource by EGS:(1)the hydraulic fracturing technology for HDR reservoirs,including reservoir reconstruction methods,hydraulic fracturing network forming mechanisms and fracture propagation prediction models is illustrated in detail;(2)the fracture characterization methods,mathematical models and solution methods are described from three aspects including pore-scale multi-field coupled models,reservoir-scale multi-field coupled models and upscaling methods;(3)the efficient extraction technology of wellbore thermal fluid,involving the mechanism of flashing flows in geothermal wells and the experimental and numerical methods for investigating the characteristics offlashing flows are discussed;(4)the HDR geothermal power generation technologies,considering the principles of geothermal power generation,the types of power generation systems and the main application markets are introduced.In conclusion,EGS is a technology-intensive system,however,due to the complex working conditions of the underground reservoirs and the instability of the ground equipment,theoretical research tends to be separated from the practice.For the purpose of promoting the applicability of EGS,intimate combination and mutual guidance with the pilot tests are necessary to develop a production-research combined mode,and to raise the awareness and break through the key points in a constant back-and-forth.
基金financial support provided by the National Key Research and Development Program of China(No.2018YFB1501805)China Geological Survey Project(Grant No.DD2019135,and No.DD20211336)。
文摘As a potentially viable renewable energy, Enhanced Geothermal Systems(EGSs) extract heat from hot dry rock(HDR) reservoirs to produce electricity and heat, which promotes the progress towards carbon peaking and carbon neutralization. The main challenge for EGSs is to reduce the investment cost. In the present study, thermo-economic investigations of EGS projects are conducted. The effects of geofluid mass flow rate, wellhead temperature and loss rate on the thermo-economic performance of the EGS organic Rankine cycle(ORC) are studied. A performance comparison between EGS-ORC and the EGS combined heating and power system(CHP) is presented. Considering the CO_(2)emission reduction benefits, the influence of carbon emission trading price on the levelized cost of energy(LCOE) is also presented. It is indicated that the geofluid mass flow rate is a critical parameter in dictating the success of a project. Under the assumed typical working conditions, the LCOE of EGS-ORC and EGS-CHP systems are 24.72 and 16.1 cents/k Wh, respectively. Compared with the EGS-ORC system, the LCOE of the EGS-CHP system is reduced by 35%. EGS-CHP systems have the potential to be economically viable in the future. With carbon emission trading prices of 12.76 USD/ton, the LCOE can be reduced by approximately 8.5%.
文摘Geothermal energy from deep underground (or geological) formations,with or without its combination with carbon capture and storage (CCS),can be a key technology to mitigate anthropogenic greenhouse gas emissions and meet the 2050 net‐zero carbon emission target.Geothermal resources in low‐permeability and medium‐and high‐temperature reservoirs in sedimentary sequence require hydraulic stimulation for enhanced geothermal systems (EGS).However,fluid migration for geothermal energy in EGS or with potential CO_(2) storage in a CO_(2)‐EGS are both dependent on the in situ flow pathway network created by induced fluid injection.These thermo‐mechanical interactions can be complex and induce varying alterations in the mechanical response when the working fluid is water (in EGS) or supercritical CO_(2)(in CO_(2)‐EGS),which could impact the geothermal energy recovery from geological formations.Therefore,there is a need for a deeper understanding of the heat extraction process in EGS and CO_(2)‐EGS.This study presents a systematic review of the effects of changes in mechanical properties and behavior of deep underground rocks on the induced flow pathway and heat recovery in EGS reservoirs with or without CO_(2) storage in CO_(2) ‐EGS.Further,we proposed waterless‐stimulated EGS as an alternative approach to improve heat energy extraction in EGS.Lastly,based on the results of our literature review and proposed ideas,we recommend promising areas of investigation that may provide more insights into understanding geothermo‐mechanics to further stimulate new research studies and accelerate the development of geothermal energy as a viable clean energy technology.
文摘Post shut‐in seismic events in enhanced geothermal systems(EGSs)occur predominantly at the outer rim of the co‐injection seismic cloud.The concept of postinjection fracture and fault closure near the injection well has been proposed and validated as a mechanism for enhancing post shut‐in pressure diffusion that promotes seismic hazard.This phenomenon is primarily attributed to the poro‐elastic closure of fractures resulting from the reduction of wellbore pressure after injection termination.However,the thermal effects in EGSs,mainly including heat transfer and thermal stress,may not be trivial and their role in postinjection fault closure and pressure evolution needs to be explored.In this study,we performed numerical simulations to analyze the relative importance of poro‐elasticity,heat transfer,and thermo‐elasticity in promoting postinjection fault closure and pressure diffusion.The numerical model wasfirst validated against analytical solutions in terms offluid pressure diffusion and against heatedflow‐through experiments in terms of thermal processes.We then quantified and distinguished the contribution of each individual mechanism by comparing four different shut‐in scenarios simulated under different coupled conditions.Our results highlight the importance of poro‐elastic fault closure in promoting postinjection pressure buildup and seismicity,and suggest that heat transfer can further augment the fault closure‐induced pressure increase and thus potentially intensify the postinjection seismic hazard,with minimal contribution from thermo‐elasticity.
基金supported by the Hebei Province Graduate Innovation Funding Project(CXZZBS2022029).
文摘With the development of industrial activities,global warming has accelerated due to excessive emission of CO_(2).Enhanced Geothermal System(EGS)utilizes deep geothermal heat for power generation.Although porous medium theory is commonly employed to model geothermal reservoirs in EGS,Hot Dry Rock(HDR)presents a challenge as it consists of impermeable granite with zero porosity,potentially distorting the physical interpretation.To address this,the Lattice Boltzmann Method(LBM)is employed to simulate CO_(2)flow within geothermal reservoirs and the Finite Volume Method(FVM)to solve the energy conservation equation for temperature distribution.This combined method of LBM and FVM is imple-mented using MATLAB.The results showed that the Reynolds numbers(Re)of 3,000 and 8,000 lead to higher heat extraction rates from geothermal reservoirs.However,higher Re values may accelerate thermal breakthrough,posing challenges to EGS operation.Meanwhile,non-equilibrium of density in fractures becomes more pronounced during the system's life cycle,with non-Darcy's law becoming significant at Re values of 3,000 and 8,000.Density stratification due to buoyancy effects significantly impacts temperature distribution within geothermal reservoirs,with buoyancy effects at Re=100 under gravitational influence being noteworthy.Larger Re values(3,000 and 8,000)induce stronger forced convection,leading to more uniform density distribution.The addition of proppant negatively affects heat transfer performance in geothermal reservoirs,especially in single fractures.Practical engineering considerations should determine the quantity of proppant through detailed numerical simulations.
