Effects of fracture evolution and non-Darcy flow on the thermal performance of enhanced geothermal system in 3D complex fractured rock

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.

Geothermo-mechanical alterations due to heat energy extraction in enhanced geothermal systems: Overview and prospective directions

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.

A combined method using Lattice Boltzmann Method(LBM)and Finite Volume Method(FVM)to simulate geothermal reservoirs in Enhanced Geothermal System(EGS)

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.

Catalog of Enhanced Geothermal Systems based on Heat Sources

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.

Comparative Study of Acid and Alkaline Stimulants with Granite in an Enhanced Geothermal System

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.

Thermo-economic Investigation of an Enhanced Geothermal System Organic Rankine Cycle and Combined Heating and Power System

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%.

The role of temperature‐enhanced fault closure in promoting postinjection pressure diffusion and seismicity in enhanced geothermal systems

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.

Conventional Geothermal Systems and Unconventional Geothermal Developments: An Overview

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.

Geothermal Power Generation Potential in the Eastern Linqing Depression

China has been the leading country worldwide in direct geothermal utilization for a rather long time, which has contributed significantly to reducing carbon emissions. But the installed capacity of geothermal power generation in China is very small, and there are only a few geothermal power plants in China, specifically in Tibet, including the well-known Yangbajing geothermal power plant. Therefore, it is anticipated that more high-temperature geothermal resources will be discovered in order to promote China’s power generation. There is potential for high-enthalpy geothermal in the Eastern Linqing Depression in Shandong Province, where geothermal energy is stored in Ordovician and Cambrian carbonate strata. Based on the geothermal gradient in Cenozoic strata and the depth of the target geothermal reservoir, the temperature distribution pattern of the reservoir was analyzed, and two "sweet points" were identified in the Yucheng geothermal field and the Guanxian geothermal field, where the reservoir temperature is predicted to be higher than 200°C at a depth of less than 8000 m. Due to the low karst fissure ratio and the insufficient geothermal fluid in the geothermal reservoir, it is recommended that an enhanced geothermal system be set up, to increase the permeability of the natural fracture system in the carbonate formations and provide sufficient fluid for power generation through reinjection of used geothermal fluid. The power generation capacity of the two geothermal fields was estimated using a volumetric method, revealing a power generation capacity of 1621.02 MWe for the Yucheng geothermal field, and 1287.19 MWe for the Guanxian geothermal field.

Fracture propagation laws of staged hydraulic fracture in fractured geothermal reservoir based on phase field model

Hydraulic fracturing is widely used in geothermal resource exploitation, and many natural fractures exist in hot dry rock reservoirs due to in-situ stress and faults. However, the infuence of natural fractures on hydraulic fracture propagation is not considered in the current study. In this paper, based on the phase feld model, a thermo-hydro-mechanical coupled hydraulic fracture propagation model was established to reveal the infuence of injection time, fracturing method, injection fow rate, and natural fracture distribution on the fracture propagation mechanism. The results show that fracture complexity increases with an increase in injection time. The stress disturbance causes the fracture initiation pressure of the second cluster signifcantly higher than that of the frst and third clusters. The zipper-type fracturing method can reduce the degree of stress disturbance and increase fracture complexity by 7.2% compared to simultaneous hydraulic fracturing. Both low and high injection fow rate lead to a decrease in fracture propagation time, which is not conducive to an increase in fracture complexity. An increase in the natural fracture angle leads to hydraulic fracture crossing natural fracture, but has a lesser efect on fracture complexity. In this paper, we analyzed the infuence of diferent factors on initiation pressure and fracture complexity, providing valuable guidance for the exploitation of geothermal resources.

Performance Characteristics of Geothermal Single Well for Building Heating

The single well geothermal heating(SWGH)technology has attracted extensive attention.To enhance heat extraction from SWGH,a mathematical model describing heat transfer is set up,and the key influence factor and heat transfer enhancement method are discussed by thermal resistance analysis.The numerical results show that the thermal resistance of rock is far greater than that of well wall and fluid.So,reducing rock thermal resistance is the most effective method for enhancing the heat extraction power.For geothermal well planning to drill:rock thermal resistance can be reduced by increasing well diameter and rock thermal conductivity;the temperature difference between liquid and rock can be raised by increasing well depth.For already existing geothermal well:an insulator with thermal conductivity of 0.2 W/(mK)is sufficient to preserve fluid enthalpy;a decrease in injection water temperature causes the increase of heat extraction power from geothermal well and heat output from heat pump simultaneously;increasing injection velocity causes the increase of pump power consumption and heat extraction power from geothermal well as well as net heat output between them.The entrepreneurs may refer to the above data in actual project.Furthermore,filling composite materials with high thermal conductivity into leakage formation is proposed in order to reduce the thermal resistance of rocks.

Investigations of Water Flow Behaviors Induced by Local Temperature Variations through a Single Rough Fracture for the Enhanced Geothermal Systems

In recent years,Enhanced Geothermal System(EGS)technologies have been applied to the geothermal resources production in the Hot Dry Rock(HDR).The core of EGS technologies is to adopt hydraulic fracturing in the reservoir to create a connected network of discrete fractures with the consideration of water as a working fluid for hydraulic fracturing and heat production.This paper investigates the characteristics of water flow behaviors through a single rough fracture under different temperature and pressure conditions.A single fracture model with rough fracture surfaces is constructed and then characterized,and influences of the anisotropic factor on the average tortuosity and frictional resistance coefficient of water flow through a single fracture with rough surfaces have been compared and analyzed.With consideration of other impacting factors(temperature,pressure,fracture roughness),the impact of mass flow rate has also been presented.Numerical simulation results present that changes of average tortuosity for water flow through a single rough facture are mainly affected by temperature.It can be observed that higher temperature leads to larger average tortuosity but the frictional resistance coefficient shows an opposite trend.As for pressure conditions,it is found that effects of pressure on average tortuosity and frictional resistance coefficient is very small,which can be neglected under high pressure conditions.Furthermore,the average tortuosity shows a progressively linear relationship with the mass flow rate.On the contrary,the frictional resistance coefficient has a negative relationship with the mass flow rate.It is revealed that when the mass flow rate reaches a critical point,the influences of temperature on the frictional resistance coefficient will be negligible.Comparisons of single rough fractures with different anisotropic factors show that values of average tortuosity and frictional resistance coefficient have positive relationships with the increase of anisotropic factors.

Multi-criteria decision-making method for evaluation of investment in enhanced geothermal systems projects

Deep geothermal energy presents large untapped renewable energy potential could significantly contribute to global energy needs. However, developing geothermal projects involves uncertainties regarding adequate geothermal brine extraction and huge costs related to preparation phases and consequently drilling and stimulation activities. Therefore, evaluating utilization alternatives of such projects is a complex decision-making problem effectively addressed using multi-criteria decision-making (MCDM) methods. This study introduces the MCDM method utilizing analytic hierarchy process (AHP) and weighted decision matrix (WDM) to assess different utilization alternatives (electricity generation, direct heat use and cogeneration). The AHP method determines the weight of each criterion and sub-criterion, while the WDM calculates the final project grade. Five criteria groups - technological, geological, economic, societal and environmental – comprising twenty-eight influencing factors were selected and used for the assessment of investment in Enhanced Geothermal Systems (EGS) projects. The AHP-WDM method was used by 38 experts from six categories: industry, educational institution, research and technology organization (RTO), small- and medium-sized enterprises (SME), local community and other. These diverse expert inputs aimed to capture varying perspectives and knowledge influence investment decisions in geothermal energy. The results were analysed accordingly. The results underscore the importance of incorporating different viewpoints to develop robust, credible, and effective investment strategies for EGS projects. Therefore, this method will contribute to more efficient EGS project development, enabling thus a greater penetration of the EGS into the market. Additionally, the proposed AHP-WDM method was implemented for a case study examining two locations. Locations were assessed and compared on scenario-based evaluation. The results confirmed the method's adequacy for assessing various end uses and comparing project feasibility across different locations.

Influences of Reservoir Heterogeneity and Anisotropy on CO_2 Sequestration and Heat Extraction for CO_2-Based Enhanced Geothermal System

Enhanced geothermal systems(EGS) have a great potential to extract geothermal energy and have attracted much interest. In this paper, based on a 3D thermal-hydrologic model considering CO_2 sequestration, the influences of reservoir heterogeneity and anisotropy on CO_2 sequestration and heat extraction in CO_2-based EGS are investigated. Different heterogeneous reservoirs and homogeneous reservoir are compared, and different ratios among reservoir permeability components are compared. The results show that greater reservoir heterogeneity enhances CO_2 sequestration and restrains heat extraction. Higher ratio between horizontal(x and y directions) and vertical permeability components enhances CO_2 sequestration and heat extraction, and vertical permeability component has a little effect. With the increasing ratio between x-directional(perpendicular to the line of the injection well and the production well) and y-directional(perpendicular to x direction) reservoir permeability components(i.e. kx:ky), both CO_2 sequestration amount and steady-state heat extraction rate first increase and then decrease, and thermal breakthrough time increases, showing that there exists an optimum kx:ky, which is about 1:1. The results of this paper indicate that reservoir heterogeneity and anisotropy have important influences on CO_2 sequestration and heat extraction.

Numerical Simulation Study of a Novel Horizontally Layered Enhanced Geothermal System:A Case Study of the Qiabuqia Geothermal Area,Qinghai Province,China

Hot dry rock,as a renewable and sustainable energy source,can alleviate resource shortages and environmental pollution.Based on data from the Qiabuqia geothermal field and an established thermal-hydrological-mechanical coupled mathematical model,a novel horizontally layered enhanced geothermal system(EGS)is proposed and compared with the conventional double vertical well EGS.Under the simulated conditions in this paper,the comprehensive heat recovery performance of the horizontally layered EGS is significantly better than that of the double vertical well EGS.Specifically,although the average production temperature of the double vertical well EGS is higher than that of the horizontally layered EGS in the attenuation stage,the heat power output of the horizontally layered EGS ranges from 6.10 MW to 12.25 MW,which is 1.36 to 1.67 times that of the double vertical well EGS.Additionally,the heat recovery rate of the horizontally layered EGS is 6.63%higher than that of the double vertical well EGS and is thus more economical.Finally,parametric analysis was performed to investigate the influence of the controllable parameters on heat recovery for the horizontally layered EGS.The heat power output and heat extraction ratio are proportional to the pressure difference and well spacing and inversely proportional to the injection fluid temperature.The thermal power output is most greatly influenced by the pressure difference,followed by the well spacing and injection fluid temperature.The effects of the pressure difference and well spacing on the heat recovery rate are almost the same,and the injection fluid temperature has no effect.

Water Storage of Water-Based Enhanced Geothermal System Based on a 3D Thermal-Hydrologic-Mechanical Model

The thermal-hydrologic-mechanical(THM)coupled processes in water-based enhanced geothermal system(EGS)greatly influence the heat extraction performance of EGS.Many THM models have been proposed,however,there is a lack of detailed analysis of water storage,which is caused by the increments of reservoir porosity and water density,and the influence of water storage on the heat extraction performance needs to be uncovered.In this paper,a 3D THM model is established to simulate the water storage amount and heat extraction rate for a water-based EGS.The 3D THM model is verified against an analytical solution.Then,the influences of water storage are investigated,and comparisons between the THM and thermal-hydrologic(TH)processes are made for different initial reservoir porosities.The results show that the increment of reservoir porosity has a larger influence on water storage than that of water density.If ignoring water storage,the injection flow rate would be underestimated,while the production flow rate and heat extraction rate would be overestimated,and the reservoir would be cooled a little slower.Compared with the TH processes,the THM processes show larger cumulative water storage amount,higher steady-state heat extraction rate and higher cooling rate of reservoir,indicating that mechanical process has important influences on EGS performances.For higher initial reservoir porosity,the cumulative water storage amount is larger.It can be inferred that the water storage amount is related to the cooling rate of reservoir.The results of this paper show that water storage has a certain influence on the heat extraction rate,and that the mechanical process and initial reservoir porosity have important effects on the water storage amount,which should be simulated based on a THM model.

Effect of temperature-dependent rock thermal conductivity and specific heat capacity on heat recovery in an enhanced geothermal system

The modeling of heat recovery from an enhanced geothermal system(EGS)requires rock thermal parameters as inputs such as thermal conductivity and specific heat capacity.These parameters may encounter significant variations due to the reduction of rock temperature during heat recovery.In the present study,we investigate the effect of temperature-dependent thermal conductivity and specific heat capacity on the thermal performance of EGS reservoirs.Equations describing the relationships between thermal conductivity/specific heat capacity and temperature from previous experimental studies were incorporated in a field-scale single-fracture EGS model.The modeling results indicate that the increase of thermal conductivity caused by temperature reduction accelerates thermal conduction from rock formations to fracture fluid,and thus improves thermal performance.The decrease of specific heat capacity due to temperature reduction,on the contrary,impairs the thermal performance but the impact is smaller than that of the increase of thermal conductivity.Due to the opposite effects of thermal conductivity increase and specific heat capacity decrease,the overall effect of temperature-dependent thermal parameters is relatively small.Assuming constant thermal parameters measured at room temperature appears to be able to provide acceptable predictions of EGS thermal performance.

美国能源部地热钻井技术研发最新部署及干热岩开发示范创新实践

与其他主要的可再生能源相比,地热能是唯一能够提供基本负载电力的能源。干热岩是指不含原生水或含少量水的高温深部岩体,可通过水力刺激改造形成增强型地热系统储层,从而提取数量可观的地热能。干热岩型地热资源的开发面临两方面主要技术挑战,一是花岗岩和玄武岩等极坚硬岩石对机械钻速的限制,二是钻井所处地层温度超过随钻测量和旋转导向等工具电子设备的运行温度上限。近年来,美国能源部资助的FORGE计划犹他州项目为测试新的钻头技术和优化钻井作业流程提供了机会,以逐步提升机械钻速并降低钻井成本。本文综述了美国能源部地热技术办公室近年发展规划中对地热钻井技术研发的部署,重点分析了犹他州项目在钻井实践过程中对基于物理限制因素重新设计的工作流程的应用,总结了美国能源部围绕地热钻井技术开展的多次规划编制以及部署实施的相关项目涉及的主要领域,以及犹他州项目在探索和实践钻井作业流程优化方面取得的认识。

美国FORGE计划犹他州干热岩开发示范项目进展综述

21世纪是全球能源获取方式发生重要变化的时代。现有以煤炭、石油、天然气等传统资源为基础的能源正在逐渐被风能、太阳能、生物质能、地热能等环境友好、低排放的绿色能源所取代。干热岩是一种不含原生水(或含少量水但不能流动)的高温地热资源,可通过水力刺激改造形成增强型地热系统储层,从而提取数量相当可观的地热能。本文以美国能源部正在组织实施的FORGE计划犹他州干热岩示范项目为研究对象,综述了项目在场地地质条件表征、基础设施建设等方面取得的主要进展与成果,总结了项目在高温硬岩钻井、储层建造、微震监测等方面取得的广泛且深入认识,从统筹部署、组织实施、场地表征和设施建设、关键技术装备突破、数据共享等方面提出了值得我国借鉴参考的具体实践。

干热岩压裂储层布井方式优选数值模拟

增强型地热系统(EGS)是从干热岩储层中提取热能的重要手段,而布井方式是影响其采热效果的关键因素,目前开展的布井方式研究较少考虑压裂储层开采模型的影响。建立了干热岩压裂储层采热的数值模型,通过不同位置的基质岩体温度下降幅度、热提取率、采出温度和采热功率对比分析了4种不同的布井方式对EGS采热性能的影响。结果表明:相较于直井,水平井的流体热交换的面积更大,能充分开发裂缝间的热量。在生产30 a时,考虑水力压裂裂缝连通的情况下,水平井一注两采模型的采热效率最高,其在垂直于井方向上温度波及范围约690 m,基质岩体平均温度下降38.09 K,热提取率为24.42%,采热功率为3.5 MW。研究成果为提高地热系统产热量、实现干热岩高效可持续开发提供了理论参考。