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
Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in buildi...Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in building energy systems,which are essential for decision-making.Therefore,this paper presents a comparative study of the performance and economic analysis of shallow and medium-deep borehole heat exchanger heating systems.Based on the geological parameters of Xi’an,China and commonly used borehole heat exchanger structures,numerical simulationmethods are employed to analyze performance and economic efficiency.The results indicate that increasing the spacing between shallow borehole heat exchangers can effectively reduce thermal interference between the pipes and improve heat extraction performance.As the flow rate increases,the outlet water temperature ranges from 279.3 to 279.7 K,with heat extraction power varying between 595 and 609 W.For medium-deep borehole heat exchangers,performance predictions show that a higher flow rate results in greater heat extraction power.However,when the flow rate exceeds 30 m^(3)/h,further increases in flow rate have only a minor effect on enhancing heat extraction power.Additionally,the economic analysis reveals that the payback period for shallow geothermal heating systems ranges from 10 to 11 years,while for medium-deep geothermal heating systems,it varies more widely from 3 to 25 years.Therefore,the payback period for medium-deep geothermal heating systems is more significantly influenced by operational and installation parameters,and optimizing these parameters can considerably shorten the payback period.The results of this study are expected to provide valuable insights into the efficient and cost-effective utilization of geothermal energy for building heating.展开更多
The rapid and accurate authentication of traditional Chinese medicines(TCMs)has always been a key scientific and technical problem in the field of pharmaceutical analysis.Herein,a novel heating online extraction elect...The rapid and accurate authentication of traditional Chinese medicines(TCMs)has always been a key scientific and technical problem in the field of pharmaceutical analysis.Herein,a novel heating online extraction electrospray ionization mass spectrometry(H-oEESI-MS)was developed for the rapid and direct analysis of extremely complex substances without the requirement for any sample pretreatment or pre-separation steps.The overall molecular profile and fragment structure features of various herbal medicines could be completely captured within 10–15 s,with minimal sample(<0.5 mg)and solvent consumption(<20μL for one sample).Furthermore,a rapid differentiation and authentication strategy for TCMs based on H-oEESI-MS was proposed,including metabolic profile characterization,characteristic marker screening and identification,and multivariate statistical analysis model validation.In an analysis of 52 batches of seven types of Aconitum medicinal materials,20 and 21 key compounds were screened out as the characteristic markers of raw and processed Aconitum herbal medicines,respectively,and the possible structures of all the characteristic markers were comprehensively identified based on Compound Discoverer databases.Finally,multivariate statistical analysis showed that all the different types of herbal medicines were well differentiated and identified(R^(2)X>0.87,R^(2)Y>0.91,and Q^(2)>0.72),which further verified the feasibility and reliability of this comprehensive strategy for the rapid authentication of different TCMs based on H-oEESI-MS.In summary,this rapid authentication strategy realized the ultra-high-throughput,low-cost,and standardized detection of various complex TCMs for the first time,thereby demonstrating wide applicability and value for the development of quality standards for TCMs.展开更多
The complex network of fractures formed by randomly distributed natural fractures in hot-dry rocks(HDRs)complicates the heat transfer regularity of injected fluid.On the basis of the fracture network,exploring the cha...The complex network of fractures formed by randomly distributed natural fractures in hot-dry rocks(HDRs)complicates the heat transfer regularity of injected fluid.On the basis of the fracture network,exploring the characteristics of the fluid flow and heat transfer as influenced by different parameters helps enable efficient resource extraction and effectively promotes the construction of diversified energy utilization structures.Accordingly,accounting for the effect of the thermal shock on the evolution of the permeability of the rock matrix,a thermo-hydromechanical(THM)coupling model is developed to analyze the influences of fracture network characteristics on the heat extraction performance of HDRs.In addition,a large-scale injection and production physical simulation experiment is performed using a newly developed,in-house,large-scale true triaxial experimental system.The corresponding numerical model is established and validated.The good agreement between the numerical and experimental results verifies the reliability and accuracy of the proposed THM model.Subsequently,a two-dimensional model is established under complex fracture network conditions,taking,as a research object,the natural fracture characteristics of HDR in the Qinghai Gonghe Basin in combination with the regional geological information.The effects of different parameters,including the production well location,rock matrix permeability,injection rate,initial fracture width,and number of fractures,on the production temperature and heat extraction performance are systematically analyzed.The results indicate that an increase in the number of fractures,the distance between the injection well and the production well,or the width of the initial fractures leads to an improved heat extraction performance.The number of fractures increased from 11 horizontal fractures and 22 high-angle fractures to 35 horizontal fractures and 70 high-angle fractures,with a 20%increase in heat extraction rate.While the influence of the rock matrix permeability is not highly significant,it cannot be ignored.It is crucial to select an injection rate that is neither too low nor too high,taking into consideration economic factors.展开更多
Metallurgical slag is a waste or by-product of the metallurgical process,and its improper disposal can pose negative environmental impacts,including groundwater and soil contamination.The composition and properties of...Metallurgical slag is a waste or by-product of the metallurgical process,and its improper disposal can pose negative environmental impacts,including groundwater and soil contamination.The composition and properties of metallurgical slag are complex,which is usually difficult to use or process directly and requires special treatment and utilization methods.Taking converter slag and blast furnace slag as examples,the research frontiers and development potential were primarily discussed and analyzed in three aspects:the recycling within and outside metallurgical slag plants,the extraction and utilization of thermal energy from metallurgical slag,and the functionalization and social application of metallurgical slag.The metallurgical slag waste heat recovery includes chemical methods and physical methods.Among them,the physical method currently most used was centrifugal granulation to recover heat.Chemical laws could recover hydrogen through the waste heat of metallurgical slag,which could save fuel and reduce CO_(2) generated by fuel combustion.Metallurgical slag is rich in alkaline metal oxides,which can undergo a carbonation reaction with CO_(2) to achieve carbon sequestration in metallurgical slag.Elements such as iron,phosphorus,and silicon contained in metallurgical slag could be used in soil conditioners,cement raw materials,and wastewater treatment.For example,the phosphorus element in the slag could be extracted by melt modification followed by acid leaching and used as a raw material for phosphate fertilizer.Therefore,under the background of China’s carbon neutrality goal,it is important to develop the key technologies of waste heat utilization of metallurgical slag and carbon sequestration of metallurgical slag.展开更多
Heat production from geothermal reservoirs is a typical heat transfer process involving a cold working fluid contacting a hot rock formation.Compared to the thermal-physical characteristics of water,supercritical CO_(...Heat production from geothermal reservoirs is a typical heat transfer process involving a cold working fluid contacting a hot rock formation.Compared to the thermal-physical characteristics of water,supercritical CO_(2)(scCO_(2))has a higher heat storage capacity over a wide temperature-pressure range and may be favored as a heat transfer fluid.Singularly characteristic of scCO_(2)-based heat extraction is that the hydraulic-thermal properties of the scCO_(2) vary dramatically and dynamically with the spatial pressure gradient during unsteady-state flow along fracture.This highly nonlinear behavior presents a challenge in the accurate estimation of heat extraction efficiency in scCO_(2)-based EGS.In this paper,a thermal-h ydraulic-mechanical(THM)coupled model is developed by considering deformation of the fractured reservoir,non-Darcy flow and the varying thermal-physical properties of scCO_(2).The proposed model is validated by matching the modeling temperature distribution with published data.The results show that during continuous injection of scCO_(2),the fracture first widens and then narrows,ultimately reopening over the long term.The sequential fracture deformation behaviors are in response to the combined impacts of mechanical compression and thermally-induced deformation.By controlling the injection parameters of the scCO_(2),it is found that the heat extraction rate is positively correlated to its pore pressure or mass flow rate.The heat extraction rate can be significantly enhanced,when the inlet temperature of scCO_(2) is below its critical temperature.As a result,the heat increment recovered per unit mass of scCO_(2) decreases as the hot rock is gradually cooled.Meanwhile,the heat increment recovered per unit mass of scCO_(2) decreases by increasing the inlet temperature of scCO_(2) or its mass flow rate,but increases as the outlet pressure rises.Furthermore,multi-linear regression indicates that controlling the inlet temperature of the scCO_(2) can significantly improve the thermodynamic efficiency of heat extraction.展开更多
Fracture networks within hot dry rock(HDR)geothermal reservoirs are complex,and heat extraction via water injection is thus a coupled process of heat-fluid-solid multifield.In this paper,utilizing the theory of normal...Fracture networks within hot dry rock(HDR)geothermal reservoirs are complex,and heat extraction via water injection is thus a coupled process of heat-fluid-solid multifield.In this paper,utilizing the theory of normally distributed random functions,we develop a corresponding pre-processing subprogram to establish a discrete network model of complex fracture distribution in HDR reservoirs;then construct a heat-fluid-solid finite element model for heat extraction via water injection and compare the numerical solution with the analytical solution of the one-dimensional non-isothermal consolidation problem for verification.The numerical simulation results show that the main factors affecting the heat extraction efficiency of HDR reservoirs include fracture width,fracture density,fracture permeability,and matrix permeability.When a HDR reservoir is injected with water for heat extraction,there is a certain threshold value of these influential parameters,beyond which the outlet temperature drops significantly,resulting in an obvious thermal breakthrough.When injecting water for heat extraction,the values of these parameters should be controlled and kept at a reasonable level,otherwise,the HDR reservoir may enter a thermal breakthrough stage in advance,which is not conducive for long-period heat extraction.Influenced by the random distribution of complex fractures,the leading edge of the cold front may present an irregular distribution.During the process of heat extraction,the stress gradually changes from a compressional state to a tensile state,which induces further damage to the HDR reservoir.展开更多
Geothermal energy,a kind of clean and environmentally friendly energy source,is an important object of future natural resource development and utilization,among which,hot dry rock is one of the important deep geotherm...Geothermal energy,a kind of clean and environmentally friendly energy source,is an important object of future natural resource development and utilization,among which,hot dry rock is one of the important deep geothermal resources.In the current multi-objective optimization of heat extraction performance,reservoir production models are less considered and the effects of different optimization ideas are not compared comprehensively.To improve the heat extraction efficiency and prolong the exploitation life of geothermal reservoirs,this paper determines the appropriate operating parameters of geothermal system(injection temperature,injection rate,production pressure and injection-production well spacing)based on the coupled thermal-hydraulic-mechanical model of hot dry rock exploitation in the Gonghe area of Qinghai and three heat extraction optimization methods.In addition,the heat extraction performances of different schemes are comparatively evaluated.And the following research results are obtained.First,the sensitivity analysis of injection and production parameters shows that power generation and recovery factor are in a reverse relation with injection-production pressure difference,which is the direct reason for the adoption of multiobjective optimization.Second,the optimization scheme prepared on the basis of parametric study indicates that the shortest life of a geothermal reservoir is 10 years,the injection-production pressure difference is up to 67 MPa,there is a significant thermal breakthrough phenomenon and the reservoir safety faces challenges.Third,by virtue of multi-objective optimization and decision making integration,the optimal operation parameter combination of hot dry rock system is determined,the life of geothermal reservoirs can exceed 20 years and balanced optimization is achieved.In conclusion,the idea of multi-objective optimization is feasible and applicable to geothermal energy exploitation and this method provides a reference for the efficient geothermal energy development and utilization and is helpful to the realization of“double carbon”goal in China.展开更多
A novel experimental setup was developed to study the heat extraction of geothermal heat exchanger(GHE)in different operational modes under adiabatic and isothermal boundaries.The experimental setup consists of a sand...A novel experimental setup was developed to study the heat extraction of geothermal heat exchanger(GHE)in different operational modes under adiabatic and isothermal boundaries.The experimental setup consists of a sand trunk,a tailored water chiller,a natural cold source unit,two water boxes containing hot water and cool water,and a data acquisition system.The experimental results indicate that the volume flow rate of the entering water is a main factor affecting the heat extraction;furthermore,the heat extraction value per meter pipe decreases gradually along the heat extraction pipe and increases with the increase of the incoming water volume flow rate.Therefore,this novel experimental setup may be helpful to further study the operation performance of GHE in different types of soil.展开更多
Oilfield geothermal energy is one important part of geothermal resources,and it can be developed and used for power generation and heating.The geothermal reserves and production ofmulti-layer sandstone oil reservoirs ...Oilfield geothermal energy is one important part of geothermal resources,and it can be developed and used for power generation and heating.The geothermal reserves and production ofmulti-layer sandstone oil reservoirs account for 50%of the total geothermal reserves and production in China,respectively,but due to the influence of interlayer heterogeneity,interlayer interference is common in the process of geothermal development by water injection.Therefore,it is in an urgent need to evaluate the heat extraction performance of oil-bearing geothermal reservoirs in multi-layer commingled production.Taking a depleted oil reservoir(and even a high-or an extra-high water-saturation oil reservoir)as the research object,this paper establishes a numerical model of coupled oilewater two-phase heat flow in a multi-layer commingled production oil reservoir.Then,interlayer interference characteristics and temperature and pressure distribution situations under different porosity,permeability and initial oil saturation are compared.Finally,the influence of interlayer interference on heat extraction performance is analyzed.And the following research results are obtained.First,under the research conditions and model settings of this paper,the injectioneproduction pressure difference and production temperature difference between low-permeability layers and high-permeability layers of the reservoir with different permeability after 20 years'production are up to 3.27MPa and 24.5 K,respectively,which are much higher than the corresponding differences of oil-bearing homogeneous reservoirs.Second,the lower the initial oil saturation,the smaller the reservoir production temperature and injectioneproduction pressure difference.And after 20 years,the maximum difference is 1.32MPa.Third,interlayer interference is sensitive to permeability.The fluid in the high-permeability layers comes from the injection well of the same layer and low-permeability layers.The production temperature of the reservoirs with different permeability can rise by 5.33 K at most.In conclusion,permeability is the key parameter influencing production temperature and injectioneproduction pressure difference of oil-bearing reservoirs while porosity has less influence on production behaviors.In addition,injectioneproduction pressure difference is more sensitive to the change of initial oil saturation and the existence of oil phase can increase the injection pressure significantly.Furthermore,if there is a boundary geothermal source,the reservoirs with strong interlayer interference can obtain high heat extraction more easily,so this type of reservoirs can be given priority in the heat extraction of abandoned wells.展开更多
Based on the independently developed true triaxial multi-physical field large-scale physical simulation system of in-situ injection and production,we conducted physical simulation of long-term multi-well injection and...Based on the independently developed true triaxial multi-physical field large-scale physical simulation system of in-situ injection and production,we conducted physical simulation of long-term multi-well injection and production in the hot dry rocks of the Gonghe Basin,Qinghai Province,NW China.Through multi-well connectivity experiments,the spatial distribution characteristics of the natural fracture system in the rock samples and the connectivity between fracture and wellbore were clarified.The injection and production wells were selected to conduct the experiments,namely one injection well and two production wells,one injection well and one production well.The variation of several physical parameters in the production well was analyzed,such as flow rate,temperature,heat recovery rate and fluid recovery.The results show that under the combination of thermal shock and injection pressure,the fracture conductivity was enhanced,and the production temperature showed a downward trend.The larger the flow rate,the faster the decrease.When the local closed area of the fracture was gradually activated,new heat transfer areas were generated,resulting in a lower rate of increase or decrease in the mining temperature.The heat recovery rate was mainly controlled by the extraction flow rate and the temperature difference between injection and production fluid.As the conductivity of the leak-off channel increased,the fluid recovery of the production well rapidly decreased.The influence mechanisms of dominant channels and fluid leak-off on thermal recovery performance are different.The former limits the heat exchange area,while the latter affects the flow rate of the produced fluid.Both of them are important factors affecting the long-term and efficient development of hot dry rock.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
In this work, the extractive distillation with heat integration process is extended to separate the pressure-insensitive benzene-cyclohexane azeotrope by using furfural as the entrainer. The optimal design of extracti...In this work, the extractive distillation with heat integration process is extended to separate the pressure-insensitive benzene-cyclohexane azeotrope by using furfural as the entrainer. The optimal design of extractive distillation process is established to achieve minimum energy requirement using the multi-objective genetic algorithm, and the results show that energy saving for this heat integration process is 15.7%. Finally, the control design is performed to investigate the system's dynamic performance, and three control structures are studied. The pressure-compensated temperature control scheme is proposed based on the first two control structures, and the dynamic responses reveal that the feed disturbances in both flow rate and benzene composition can be mitigated well.展开更多
U-type medium-deep borehole heat exchanger(U-MDBHE)is a sustainable building heating technology.Current studies assess the long-term thermal performance of U-MDBHE using typical meteorological year weather data.The co...U-type medium-deep borehole heat exchanger(U-MDBHE)is a sustainable building heating technology.Current studies assess the long-term thermal performance of U-MDBHE using typical meteorological year weather data.The conclusions indicate a discernible deterioration in the thermal performance of U-MDBHE attributed to heat extraction attenuation.The thermal performance deterioration leads to the oversize of U-MDBHE and hinders the widespread application of U-MDBHE.This study introduces a novel idea that the long-term thermal performance of U-MDBHE should be evaluated considering climate change(CC)and verifies that the favorable effects of CC on the thermal performance of U-MDBHE can effectively mitigate the adverse effect of heat extraction attenuation.The favorable effects of CC include reducing the heating demand(due to the reduced building heating load(BHL)caused by CC)and improving the heating supply capacity(due to the enhanced outlet temperature caused by CC).In addition,the reduced BHL under CC enhances the inlet temperature of U-MDBHE,thereby improving its operation safety.CC mitigates the heat extraction attenuation of U-MDBHE,with the strongest effect in the ascending well,followed by the descending well,and then the butted well.Case studies using experimentally validated simulations on the 30-year operation of U-MDBHE demonstrate that by mitigating the adverse effect of the heat extraction attenuation,CC reduces the accumulated energy consumption by 14.31%–26.59%and improves the operation safety by up to 100%in Harbin(severe cold region)and Beijing(cold region).This study significantly contributes to improving the long-term thermal performance of U-MDBHE.展开更多
Enhanced geothermal system(EGS)is subject to the comprehensive effects of multiple physicalfields during the long-term heat extraction process,including hydraulic(H),thermal(T),mechanical(M)and chemical(C)fields.The e...Enhanced geothermal system(EGS)is subject to the comprehensive effects of multiple physicalfields during the long-term heat extraction process,including hydraulic(H),thermal(T),mechanical(M)and chemical(C)fields.The embedded discrete fracture model(EDFM)can effectively simulate the variations offlow,temperature,mechanical and concentrationfields in fractured reservoirs.At present,however,the thermo-hydro-mechanical-chemical(THMC)coupling model based on EDFM is less researched.In this paper,the THMC coupling model of fractured reservoir is established based on EDFM by considering the changes in reservoir heterogeneity and physical properties as well as watererock reactions.Then,the spatiotemporal evolution offlow,temperature,displacement and concentrationfields in the operation process of EGS is simulated and analyzed.And the following research results are obtained.First,when the permeability of the basement rock is low,the production temperature decrease during exploitation is gradual,allowing EGS to maintain a high exploitation temperature for an extended period.However,lower permeability may result in a decrease in the qualityflow rate from production wells,thereby affecting net heat extraction power.Second,when fracture permeability or fracture opening changes,EGS can output higher temperature stably for a certain period and then the temperature decreases at different amplitudes.When the fracture permeability increases to a certain value or the fracture opening decreases to a certain value,the influence of the change in fracture parameters on production temperature gets weak.Third,After 40 years of EGS operation,considering variable propertyfluids results in a 22 C lower exploitation temperature compared to using constant propertyfluids,and considering watererock reactions results in a 15 C lower exploitation temperature,with a 12.5%increase in reservoir average porosity.In conclusion,when researching a long-term operating EGS,it is necessary to comprehensively consider the influences of reservoir rock parameters,physical properties of injectedfluid,watererock reaction and other factors.And in the future,attention shall be paid to the two-way coupling of chemical reaction and mechanical deformation of other mineral compositions in the reservoir to the hydro-thermo-chemicalfield influence,so as to provide more accurate and reliable prediction for the engineering development and utilization of EGS reservoirs.展开更多
The efficient exploitation of geothermal energy through enhanced geothermal systems(EGS)has been a relevant topic for hot dry rock(HDR)geothermal resources.When cryogenic fluid is injected into a thermal reservoir,imp...The efficient exploitation of geothermal energy through enhanced geothermal systems(EGS)has been a relevant topic for hot dry rock(HDR)geothermal resources.When cryogenic fluid is injected into a thermal reservoir,improving heat exchange efficiency is key to achieving the optimal exploitation of HDR.In this paper,granite outcrops from Gonghe Basin were used as the testing sample.The natural fractures in the granite samples were relatively well developed.To simulate long-term injection and production from multi-wells in situ,physical ex-periments were performed in a newly-developed,in-house large-scale true triaxial experimental system.Geothermal extraction performance of an HDR was simulated for long-term injection and production operations.Simultaneously,the mode of one-injection and multiple-production wells was represented.In the paper,the ef-fects of the production-injection well spacing,the number of production wells and the injection rate on the production temperature and flow rate are discussed.The results show that,during long-term injection and pro-duction,there are two stages of production temperature variation,namely stabilization and attenuation.When the number of the production wells is increased,the heat extraction efficiency is accelerated.Moreover,competitive diversion of fluid among fractures occurred due to different conductivities.Furthermore,under different pro-duction modes,the production flow rate contributed differently to the heat extraction.Finally,the effect of the production-injection wells spacing on the heat exchange performance was analyzed;this is mainly reflected in the change of the effective heat exchange area between the rock and the injected fluid.The results emphasize the importance of designing an appropriate production mode and optimizing the injection-production parameters to ensure efficient HDR exploitation.展开更多
Enhanced geothermal systems(EGSs)in this study are classified as fracturing-EGS(F-EGS),pipe-EGS(P-EGS)and excavation-EGS(E-EGS)according to reservoir stimulation strategies.However,the heat extraction performances of ...Enhanced geothermal systems(EGSs)in this study are classified as fracturing-EGS(F-EGS),pipe-EGS(P-EGS)and excavation-EGS(E-EGS)according to reservoir stimulation strategies.However,the heat extraction performances of three EGSs employing different stimulation strategies are not fully understood.Here,we define the region where the pore pressure increment calculated by a hydraulic fracturing process is higher than rock tensile strength as the stimulation region for establishing a more accurate F-EGS model,and then compare three geothermal systems to select a appropriate reservoir stimulation strategy.We find that the F-EGS model assuming an entire stimulated region significantly exaggerates the heat extraction results.The optimal conditions for P-EGS are low injection rates and short operation times,which is suiTablefor seasonal heating or multi-energy co-generation projects including a thermal recovery phase.Theoretically,E-EGS has better geothermal extraction performance than F-EGS based on existing model assumptions,but its construction feasibility and economics need further exploration.H2O is more suiTableas a heat exchange fluid in E-EGS than supercritical CO_(2).This study provides a reference for geothermal mining simulation and reservoir stimulation strategy selection.展开更多
As a kind of clean renewable energy,the production and utilization of geothermal resources can make a great contribution to optimizing the energy structure and energy conservation and emission reduction.The circulatin...As a kind of clean renewable energy,the production and utilization of geothermal resources can make a great contribution to optimizing the energy structure and energy conservation and emission reduction.The circulating heat extraction process of working fluid will disturb the equilibrium state of physical and chemical fields inside the reservoir,and involve the mutual coupling of heat transfer,flow,stress,and chemical reaction.Revealing the coupling mechanism of flow and heat transfer inside the reservoir during geothermal exploitation can provide important theoretical support for the efficient exploitation of geothermal resources.This paper reviews the research advances of the multi-field coupling model in the reservoir during geothermal production over the past 40 years.The thrust of this paper is on objective analysis and evaluation of the importance of each coupling process and its influence on reservoir heat extraction performance.Finally,we discuss the existing challenges and perspectives to promote the future development of the geothermal reservoir multi-field coupling model.An accurate understanding of the multi-field coupling mechanism,an efficient cross-scale modeling method,as well as the accurate characterization of reservoir fracture morphology,are crucial for the multi-field coupling model of geothermal production.展开更多
The increase of insulation thickness(IT)results in the decrease of the heat demand and heat medium temperature.A mathematical model on the optimum environmental insulation thickness(OEIT)for minimizing the annual tota...The increase of insulation thickness(IT)results in the decrease of the heat demand and heat medium temperature.A mathematical model on the optimum environmental insulation thickness(OEIT)for minimizing the annual total environmental impact was established based on the amount of energy and energy grade reduction.Besides,a case study was conducted based on a residential community with a combined heat and power(CHP)-based district heating system(DHS)in Tianjin,China.Moreover,the effect of IT on heat demand,heat medium temperature,exhaust heat,extracted heat,coal consumption,carbon dioxide(CO_(2))emissions and sulfur dioxide(SO_(2))emissions as well as the effect of three types of insulation materials(i.e.,expanded polystyrene,rock wool and glass wool)on the OEIT and minimum annual total environmental impact were studied.The results reveal that the optimization model can be used to determine the OEIT.When the OEIT of expanded polystyrene,rock wool and glass wool is used,the annual total environmental impact can be reduced by 84.563%,83.211%,and 86.104%,respectively.It can be found that glass wool is more beneficial to the environment compared with expanded polystyrene and rock wool.展开更多
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...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.展开更多
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support by the Shanghai Engineering Research Center for Shallow Geothermal Energy(DRZX-202306)Shaanxi Coal Geology Group Co.,Ltd.(SMDZ-ZD2024-23)+4 种基金Key Laboratory of Coal Resources Exploration and Comprehensive Utilization,Ministry of Natural Resources,China(ZP2020-1)Shaanxi Investment Group Co.,Ltd.(SIGC2023-KY-05)Key Research and Development Projects of Shaanxi Province(2023-GHZD-54)Shaanxi Qinchuangyuan Scientist+Engineer Team Construction Project(2022KXJ-049)China Postdoctoral Science Foundation(2023M742802,2024T170721).
文摘Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in building energy systems,which are essential for decision-making.Therefore,this paper presents a comparative study of the performance and economic analysis of shallow and medium-deep borehole heat exchanger heating systems.Based on the geological parameters of Xi’an,China and commonly used borehole heat exchanger structures,numerical simulationmethods are employed to analyze performance and economic efficiency.The results indicate that increasing the spacing between shallow borehole heat exchangers can effectively reduce thermal interference between the pipes and improve heat extraction performance.As the flow rate increases,the outlet water temperature ranges from 279.3 to 279.7 K,with heat extraction power varying between 595 and 609 W.For medium-deep borehole heat exchangers,performance predictions show that a higher flow rate results in greater heat extraction power.However,when the flow rate exceeds 30 m^(3)/h,further increases in flow rate have only a minor effect on enhancing heat extraction power.Additionally,the economic analysis reveals that the payback period for shallow geothermal heating systems ranges from 10 to 11 years,while for medium-deep geothermal heating systems,it varies more widely from 3 to 25 years.Therefore,the payback period for medium-deep geothermal heating systems is more significantly influenced by operational and installation parameters,and optimizing these parameters can considerably shorten the payback period.The results of this study are expected to provide valuable insights into the efficient and cost-effective utilization of geothermal energy for building heating.
基金supported by the CACMS Innovation Fund,China(Grant Nos.:CI2021A04504 and CI2021A05206)the National Natural Science Foundation of China(Grant Nos.:82104380,81891010,81891013,and 82074012)+2 种基金the Fundamental Research Funds for the Central Public Welfare Research Institutes,China(Grant Nos.:ZZ14-YQ-047 and ZZXT202105)the Key Project at Central Government Level(Grant No.:2060302-2201-26)the Beijing Nova Program.
文摘The rapid and accurate authentication of traditional Chinese medicines(TCMs)has always been a key scientific and technical problem in the field of pharmaceutical analysis.Herein,a novel heating online extraction electrospray ionization mass spectrometry(H-oEESI-MS)was developed for the rapid and direct analysis of extremely complex substances without the requirement for any sample pretreatment or pre-separation steps.The overall molecular profile and fragment structure features of various herbal medicines could be completely captured within 10–15 s,with minimal sample(<0.5 mg)and solvent consumption(<20μL for one sample).Furthermore,a rapid differentiation and authentication strategy for TCMs based on H-oEESI-MS was proposed,including metabolic profile characterization,characteristic marker screening and identification,and multivariate statistical analysis model validation.In an analysis of 52 batches of seven types of Aconitum medicinal materials,20 and 21 key compounds were screened out as the characteristic markers of raw and processed Aconitum herbal medicines,respectively,and the possible structures of all the characteristic markers were comprehensively identified based on Compound Discoverer databases.Finally,multivariate statistical analysis showed that all the different types of herbal medicines were well differentiated and identified(R^(2)X>0.87,R^(2)Y>0.91,and Q^(2)>0.72),which further verified the feasibility and reliability of this comprehensive strategy for the rapid authentication of different TCMs based on H-oEESI-MS.In summary,this rapid authentication strategy realized the ultra-high-throughput,low-cost,and standardized detection of various complex TCMs for the first time,thereby demonstrating wide applicability and value for the development of quality standards for TCMs.
基金supported by the Major Program of National Natural Science Foundation of China(No.52192622)the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Independent Research Project(No.SKLGP2022Z018).
文摘The complex network of fractures formed by randomly distributed natural fractures in hot-dry rocks(HDRs)complicates the heat transfer regularity of injected fluid.On the basis of the fracture network,exploring the characteristics of the fluid flow and heat transfer as influenced by different parameters helps enable efficient resource extraction and effectively promotes the construction of diversified energy utilization structures.Accordingly,accounting for the effect of the thermal shock on the evolution of the permeability of the rock matrix,a thermo-hydromechanical(THM)coupling model is developed to analyze the influences of fracture network characteristics on the heat extraction performance of HDRs.In addition,a large-scale injection and production physical simulation experiment is performed using a newly developed,in-house,large-scale true triaxial experimental system.The corresponding numerical model is established and validated.The good agreement between the numerical and experimental results verifies the reliability and accuracy of the proposed THM model.Subsequently,a two-dimensional model is established under complex fracture network conditions,taking,as a research object,the natural fracture characteristics of HDR in the Qinghai Gonghe Basin in combination with the regional geological information.The effects of different parameters,including the production well location,rock matrix permeability,injection rate,initial fracture width,and number of fractures,on the production temperature and heat extraction performance are systematically analyzed.The results indicate that an increase in the number of fractures,the distance between the injection well and the production well,or the width of the initial fractures leads to an improved heat extraction performance.The number of fractures increased from 11 horizontal fractures and 22 high-angle fractures to 35 horizontal fractures and 70 high-angle fractures,with a 20%increase in heat extraction rate.While the influence of the rock matrix permeability is not highly significant,it cannot be ignored.It is crucial to select an injection rate that is neither too low nor too high,taking into consideration economic factors.
基金supported by the following funds:Guizhou Science and Technology Support Program Project[Grant No.Guizhou Science and Technology Cooperation Support(2025)General 079]Guizhou Provincial Department of Education’s"Top 100 Schools and Thousand Enterprises in Science andTechnology Research and Development"Project in 2025(Contract Number:Guizhou Education and Technology[2025]No.009)+6 种基金Hebei Province Innovation Ability Improvement Plan(No.23561001D)Hebei Provincial Natural Science Foundation(No.H2022209089)Open Fund Project of the Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education(Grant No.FMRUlab23-03)the National Natural Science Foundation of China(No.52074128)Basic Scientific Research Business Expenses of Colleges and Universities in Hebei Province(Nos.JYG2022001 and JQN2023008)Tangshan Talent Funding Project(No.A202202007),Natural Science Foundation of Hebei Province(No.E2023209107)Foundation of Tangshan Science and Technology Bureau(No.23150219A).
文摘Metallurgical slag is a waste or by-product of the metallurgical process,and its improper disposal can pose negative environmental impacts,including groundwater and soil contamination.The composition and properties of metallurgical slag are complex,which is usually difficult to use or process directly and requires special treatment and utilization methods.Taking converter slag and blast furnace slag as examples,the research frontiers and development potential were primarily discussed and analyzed in three aspects:the recycling within and outside metallurgical slag plants,the extraction and utilization of thermal energy from metallurgical slag,and the functionalization and social application of metallurgical slag.The metallurgical slag waste heat recovery includes chemical methods and physical methods.Among them,the physical method currently most used was centrifugal granulation to recover heat.Chemical laws could recover hydrogen through the waste heat of metallurgical slag,which could save fuel and reduce CO_(2) generated by fuel combustion.Metallurgical slag is rich in alkaline metal oxides,which can undergo a carbonation reaction with CO_(2) to achieve carbon sequestration in metallurgical slag.Elements such as iron,phosphorus,and silicon contained in metallurgical slag could be used in soil conditioners,cement raw materials,and wastewater treatment.For example,the phosphorus element in the slag could be extracted by melt modification followed by acid leaching and used as a raw material for phosphate fertilizer.Therefore,under the background of China’s carbon neutrality goal,it is important to develop the key technologies of waste heat utilization of metallurgical slag and carbon sequestration of metallurgical slag.
基金The financial support from the National Natural Science Foundation of China(Nos.41772154 and 42102338)Natural Science Foundation of Shandong Province(Nos.ZR2019MA009 and ZR2020QE115)SDUST Research Fund of China(No.2018TDJH102)。
文摘Heat production from geothermal reservoirs is a typical heat transfer process involving a cold working fluid contacting a hot rock formation.Compared to the thermal-physical characteristics of water,supercritical CO_(2)(scCO_(2))has a higher heat storage capacity over a wide temperature-pressure range and may be favored as a heat transfer fluid.Singularly characteristic of scCO_(2)-based heat extraction is that the hydraulic-thermal properties of the scCO_(2) vary dramatically and dynamically with the spatial pressure gradient during unsteady-state flow along fracture.This highly nonlinear behavior presents a challenge in the accurate estimation of heat extraction efficiency in scCO_(2)-based EGS.In this paper,a thermal-h ydraulic-mechanical(THM)coupled model is developed by considering deformation of the fractured reservoir,non-Darcy flow and the varying thermal-physical properties of scCO_(2).The proposed model is validated by matching the modeling temperature distribution with published data.The results show that during continuous injection of scCO_(2),the fracture first widens and then narrows,ultimately reopening over the long term.The sequential fracture deformation behaviors are in response to the combined impacts of mechanical compression and thermally-induced deformation.By controlling the injection parameters of the scCO_(2),it is found that the heat extraction rate is positively correlated to its pore pressure or mass flow rate.The heat extraction rate can be significantly enhanced,when the inlet temperature of scCO_(2) is below its critical temperature.As a result,the heat increment recovered per unit mass of scCO_(2) decreases as the hot rock is gradually cooled.Meanwhile,the heat increment recovered per unit mass of scCO_(2) decreases by increasing the inlet temperature of scCO_(2) or its mass flow rate,but increases as the outlet pressure rises.Furthermore,multi-linear regression indicates that controlling the inlet temperature of the scCO_(2) can significantly improve the thermodynamic efficiency of heat extraction.
基金This work is financially supported by the National Science Foundation of China(Grant No.52192622,No.51936001,No.52274002,No.51804033 and No.U20A20265)Beijing Natural Science Foundation(Grant No.3222030)+2 种基金the PetroChina Science and Technology Innovation Foundation Project(2021DQ02e0201)the Award Cultivation Foundation from Beijing Institute of Petrochemical Technology(Grant No.BIPTACF-002)the Fund of the Beijing Municipal Education Commission(Grant No.22019821001).
文摘Fracture networks within hot dry rock(HDR)geothermal reservoirs are complex,and heat extraction via water injection is thus a coupled process of heat-fluid-solid multifield.In this paper,utilizing the theory of normally distributed random functions,we develop a corresponding pre-processing subprogram to establish a discrete network model of complex fracture distribution in HDR reservoirs;then construct a heat-fluid-solid finite element model for heat extraction via water injection and compare the numerical solution with the analytical solution of the one-dimensional non-isothermal consolidation problem for verification.The numerical simulation results show that the main factors affecting the heat extraction efficiency of HDR reservoirs include fracture width,fracture density,fracture permeability,and matrix permeability.When a HDR reservoir is injected with water for heat extraction,there is a certain threshold value of these influential parameters,beyond which the outlet temperature drops significantly,resulting in an obvious thermal breakthrough.When injecting water for heat extraction,the values of these parameters should be controlled and kept at a reasonable level,otherwise,the HDR reservoir may enter a thermal breakthrough stage in advance,which is not conducive for long-period heat extraction.Influenced by the random distribution of complex fractures,the leading edge of the cold front may present an irregular distribution.During the process of heat extraction,the stress gradually changes from a compressional state to a tensile state,which induces further damage to the HDR reservoir.
基金National Natural Science Foundation of China(NSFC)“Theory and Technology of Complex Seam Network in High Temperature Rock for Storage”(No.52192621)National Key Research and Development Program(No.2018YFB1501804)+2 种基金Sichuan Science and Technology Program Project“Research on the Mechanism of Enhanced Heat Transfer between Geothermal Well Completion Structure and Downhole Heat Exchanger”(No.2021Ya1.389)National Key Research and Development Program(No.2021YJ0389)“Research on the Mechanism of Fracture Damage in Dry Hot Rock Extraction”(PRP/open-2110)of the State Key Laboratory of Oil and Gas Resources and Exploration,China University of Petroleum(Beijing).
文摘Geothermal energy,a kind of clean and environmentally friendly energy source,is an important object of future natural resource development and utilization,among which,hot dry rock is one of the important deep geothermal resources.In the current multi-objective optimization of heat extraction performance,reservoir production models are less considered and the effects of different optimization ideas are not compared comprehensively.To improve the heat extraction efficiency and prolong the exploitation life of geothermal reservoirs,this paper determines the appropriate operating parameters of geothermal system(injection temperature,injection rate,production pressure and injection-production well spacing)based on the coupled thermal-hydraulic-mechanical model of hot dry rock exploitation in the Gonghe area of Qinghai and three heat extraction optimization methods.In addition,the heat extraction performances of different schemes are comparatively evaluated.And the following research results are obtained.First,the sensitivity analysis of injection and production parameters shows that power generation and recovery factor are in a reverse relation with injection-production pressure difference,which is the direct reason for the adoption of multiobjective optimization.Second,the optimization scheme prepared on the basis of parametric study indicates that the shortest life of a geothermal reservoir is 10 years,the injection-production pressure difference is up to 67 MPa,there is a significant thermal breakthrough phenomenon and the reservoir safety faces challenges.Third,by virtue of multi-objective optimization and decision making integration,the optimal operation parameter combination of hot dry rock system is determined,the life of geothermal reservoirs can exceed 20 years and balanced optimization is achieved.In conclusion,the idea of multi-objective optimization is feasible and applicable to geothermal energy exploitation and this method provides a reference for the efficient geothermal energy development and utilization and is helpful to the realization of“double carbon”goal in China.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50378024)
文摘A novel experimental setup was developed to study the heat extraction of geothermal heat exchanger(GHE)in different operational modes under adiabatic and isothermal boundaries.The experimental setup consists of a sand trunk,a tailored water chiller,a natural cold source unit,two water boxes containing hot water and cool water,and a data acquisition system.The experimental results indicate that the volume flow rate of the entering water is a main factor affecting the heat extraction;furthermore,the heat extraction value per meter pipe decreases gradually along the heat extraction pipe and increases with the increase of the incoming water volume flow rate.Therefore,this novel experimental setup may be helpful to further study the operation performance of GHE in different types of soil.
基金National Natural Science Foundation of China major project“High-temperature rock dynamic damage mechanism and high-efficiency crushing method”(No.52192624)National Natural Science Foundation of China key research and development plan project“Multi-field coupled flow heat transfer mechanism and heat extraction performance optimization in thermal storage”(No.:2018YFB1501804)China University of Petroleum(Beijing)State Key Laboratory of Oil and Gas Resources and Exploration Fund Project“Research on Fracture Damage Mechanism during Hot Dry Rock Exploitation”(No.PRP/open-2110).
文摘Oilfield geothermal energy is one important part of geothermal resources,and it can be developed and used for power generation and heating.The geothermal reserves and production ofmulti-layer sandstone oil reservoirs account for 50%of the total geothermal reserves and production in China,respectively,but due to the influence of interlayer heterogeneity,interlayer interference is common in the process of geothermal development by water injection.Therefore,it is in an urgent need to evaluate the heat extraction performance of oil-bearing geothermal reservoirs in multi-layer commingled production.Taking a depleted oil reservoir(and even a high-or an extra-high water-saturation oil reservoir)as the research object,this paper establishes a numerical model of coupled oilewater two-phase heat flow in a multi-layer commingled production oil reservoir.Then,interlayer interference characteristics and temperature and pressure distribution situations under different porosity,permeability and initial oil saturation are compared.Finally,the influence of interlayer interference on heat extraction performance is analyzed.And the following research results are obtained.First,under the research conditions and model settings of this paper,the injectioneproduction pressure difference and production temperature difference between low-permeability layers and high-permeability layers of the reservoir with different permeability after 20 years'production are up to 3.27MPa and 24.5 K,respectively,which are much higher than the corresponding differences of oil-bearing homogeneous reservoirs.Second,the lower the initial oil saturation,the smaller the reservoir production temperature and injectioneproduction pressure difference.And after 20 years,the maximum difference is 1.32MPa.Third,interlayer interference is sensitive to permeability.The fluid in the high-permeability layers comes from the injection well of the same layer and low-permeability layers.The production temperature of the reservoirs with different permeability can rise by 5.33 K at most.In conclusion,permeability is the key parameter influencing production temperature and injectioneproduction pressure difference of oil-bearing reservoirs while porosity has less influence on production behaviors.In addition,injectioneproduction pressure difference is more sensitive to the change of initial oil saturation and the existence of oil phase can increase the injection pressure significantly.Furthermore,if there is a boundary geothermal source,the reservoirs with strong interlayer interference can obtain high heat extraction more easily,so this type of reservoirs can be given priority in the heat extraction of abandoned wells.
基金Supported by the National Natural Science Foundation of China(52192622,52304003).
文摘Based on the independently developed true triaxial multi-physical field large-scale physical simulation system of in-situ injection and production,we conducted physical simulation of long-term multi-well injection and production in the hot dry rocks of the Gonghe Basin,Qinghai Province,NW China.Through multi-well connectivity experiments,the spatial distribution characteristics of the natural fracture system in the rock samples and the connectivity between fracture and wellbore were clarified.The injection and production wells were selected to conduct the experiments,namely one injection well and two production wells,one injection well and one production well.The variation of several physical parameters in the production well was analyzed,such as flow rate,temperature,heat recovery rate and fluid recovery.The results show that under the combination of thermal shock and injection pressure,the fracture conductivity was enhanced,and the production temperature showed a downward trend.The larger the flow rate,the faster the decrease.When the local closed area of the fracture was gradually activated,new heat transfer areas were generated,resulting in a lower rate of increase or decrease in the mining temperature.The heat recovery rate was mainly controlled by the extraction flow rate and the temperature difference between injection and production fluid.As the conductivity of the leak-off channel increased,the fluid recovery of the production well rapidly decreased.The influence mechanisms of dominant channels and fluid leak-off on thermal recovery performance are different.The former limits the heat exchange area,while the latter affects the flow rate of the produced fluid.Both of them are important factors affecting the long-term and efficient development of hot dry rock.
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.
基金supported by the National Natural Science Foundation of China(grant number 21476261)the Key Research and Development Plan Project of Shandong Province(grant number 2015GGX107004)
文摘In this work, the extractive distillation with heat integration process is extended to separate the pressure-insensitive benzene-cyclohexane azeotrope by using furfural as the entrainer. The optimal design of extractive distillation process is established to achieve minimum energy requirement using the multi-objective genetic algorithm, and the results show that energy saving for this heat integration process is 15.7%. Finally, the control design is performed to investigate the system's dynamic performance, and three control structures are studied. The pressure-compensated temperature control scheme is proposed based on the first two control structures, and the dynamic responses reveal that the feed disturbances in both flow rate and benzene composition can be mitigated well.
基金supported by the Key Research and Development Projects of Shaanxi Province(Project No.2024SF-YBXM-596 and Project No.2024SF-YBXM-604)Special Fund Project of Science and Technology Innovation by Shaanxi Provincial State-owned Capital Management Budget(Project No.31228000000008/011900)+2 种基金Top Young Talent Programme of Xi’an Jiaotong University(Project No.011900/11301224030703)Qin Chuangyuan“Scientist+Engineer”Team Program(Project No.2022KXJ-039)Innovation Capability Support Program of Shaanxi Province(Project No.2021PT-028).
文摘U-type medium-deep borehole heat exchanger(U-MDBHE)is a sustainable building heating technology.Current studies assess the long-term thermal performance of U-MDBHE using typical meteorological year weather data.The conclusions indicate a discernible deterioration in the thermal performance of U-MDBHE attributed to heat extraction attenuation.The thermal performance deterioration leads to the oversize of U-MDBHE and hinders the widespread application of U-MDBHE.This study introduces a novel idea that the long-term thermal performance of U-MDBHE should be evaluated considering climate change(CC)and verifies that the favorable effects of CC on the thermal performance of U-MDBHE can effectively mitigate the adverse effect of heat extraction attenuation.The favorable effects of CC include reducing the heating demand(due to the reduced building heating load(BHL)caused by CC)and improving the heating supply capacity(due to the enhanced outlet temperature caused by CC).In addition,the reduced BHL under CC enhances the inlet temperature of U-MDBHE,thereby improving its operation safety.CC mitigates the heat extraction attenuation of U-MDBHE,with the strongest effect in the ascending well,followed by the descending well,and then the butted well.Case studies using experimentally validated simulations on the 30-year operation of U-MDBHE demonstrate that by mitigating the adverse effect of the heat extraction attenuation,CC reduces the accumulated energy consumption by 14.31%–26.59%and improves the operation safety by up to 100%in Harbin(severe cold region)and Beijing(cold region).This study significantly contributes to improving the long-term thermal performance of U-MDBHE.
基金supported by Key Fund of the National Natural Science Foundation of China“A Study on the Mechanism of Heat and Mass Transfer in the Coupled THMC of Strong Geothermal System”(No.51936001)Open Fund Project of National Key Laboratory for Energy Efficiency and Clean Utilization(No.ZJUCEU2022001).
文摘Enhanced geothermal system(EGS)is subject to the comprehensive effects of multiple physicalfields during the long-term heat extraction process,including hydraulic(H),thermal(T),mechanical(M)and chemical(C)fields.The embedded discrete fracture model(EDFM)can effectively simulate the variations offlow,temperature,mechanical and concentrationfields in fractured reservoirs.At present,however,the thermo-hydro-mechanical-chemical(THMC)coupling model based on EDFM is less researched.In this paper,the THMC coupling model of fractured reservoir is established based on EDFM by considering the changes in reservoir heterogeneity and physical properties as well as watererock reactions.Then,the spatiotemporal evolution offlow,temperature,displacement and concentrationfields in the operation process of EGS is simulated and analyzed.And the following research results are obtained.First,when the permeability of the basement rock is low,the production temperature decrease during exploitation is gradual,allowing EGS to maintain a high exploitation temperature for an extended period.However,lower permeability may result in a decrease in the qualityflow rate from production wells,thereby affecting net heat extraction power.Second,when fracture permeability or fracture opening changes,EGS can output higher temperature stably for a certain period and then the temperature decreases at different amplitudes.When the fracture permeability increases to a certain value or the fracture opening decreases to a certain value,the influence of the change in fracture parameters on production temperature gets weak.Third,After 40 years of EGS operation,considering variable propertyfluids results in a 22 C lower exploitation temperature compared to using constant propertyfluids,and considering watererock reactions results in a 15 C lower exploitation temperature,with a 12.5%increase in reservoir average porosity.In conclusion,when researching a long-term operating EGS,it is necessary to comprehensively consider the influences of reservoir rock parameters,physical properties of injectedfluid,watererock reaction and other factors.And in the future,attention shall be paid to the two-way coupling of chemical reaction and mechanical deformation of other mineral compositions in the reservoir to the hydro-thermo-chemicalfield influence,so as to provide more accurate and reliable prediction for the engineering development and utilization of EGS reservoirs.
文摘The efficient exploitation of geothermal energy through enhanced geothermal systems(EGS)has been a relevant topic for hot dry rock(HDR)geothermal resources.When cryogenic fluid is injected into a thermal reservoir,improving heat exchange efficiency is key to achieving the optimal exploitation of HDR.In this paper,granite outcrops from Gonghe Basin were used as the testing sample.The natural fractures in the granite samples were relatively well developed.To simulate long-term injection and production from multi-wells in situ,physical ex-periments were performed in a newly-developed,in-house large-scale true triaxial experimental system.Geothermal extraction performance of an HDR was simulated for long-term injection and production operations.Simultaneously,the mode of one-injection and multiple-production wells was represented.In the paper,the ef-fects of the production-injection well spacing,the number of production wells and the injection rate on the production temperature and flow rate are discussed.The results show that,during long-term injection and pro-duction,there are two stages of production temperature variation,namely stabilization and attenuation.When the number of the production wells is increased,the heat extraction efficiency is accelerated.Moreover,competitive diversion of fluid among fractures occurred due to different conductivities.Furthermore,under different pro-duction modes,the production flow rate contributed differently to the heat extraction.Finally,the effect of the production-injection wells spacing on the heat exchange performance was analyzed;this is mainly reflected in the change of the effective heat exchange area between the rock and the injected fluid.The results emphasize the importance of designing an appropriate production mode and optimizing the injection-production parameters to ensure efficient HDR exploitation.
文摘Enhanced geothermal systems(EGSs)in this study are classified as fracturing-EGS(F-EGS),pipe-EGS(P-EGS)and excavation-EGS(E-EGS)according to reservoir stimulation strategies.However,the heat extraction performances of three EGSs employing different stimulation strategies are not fully understood.Here,we define the region where the pore pressure increment calculated by a hydraulic fracturing process is higher than rock tensile strength as the stimulation region for establishing a more accurate F-EGS model,and then compare three geothermal systems to select a appropriate reservoir stimulation strategy.We find that the F-EGS model assuming an entire stimulated region significantly exaggerates the heat extraction results.The optimal conditions for P-EGS are low injection rates and short operation times,which is suiTablefor seasonal heating or multi-energy co-generation projects including a thermal recovery phase.Theoretically,E-EGS has better geothermal extraction performance than F-EGS based on existing model assumptions,but its construction feasibility and economics need further exploration.H2O is more suiTableas a heat exchange fluid in E-EGS than supercritical CO_(2).This study provides a reference for geothermal mining simulation and reservoir stimulation strategy selection.
基金the National Natural Science Fund for Major Program of China(Grant No.52192621)the National Natural Science Fund for Major Program of China(Grant No.52192624)+1 种基金the National Key Research and Development Program of China(Grant No.2018YFB1501804)Sichuan Science and Technology Program(2021YJ0389).
文摘As a kind of clean renewable energy,the production and utilization of geothermal resources can make a great contribution to optimizing the energy structure and energy conservation and emission reduction.The circulating heat extraction process of working fluid will disturb the equilibrium state of physical and chemical fields inside the reservoir,and involve the mutual coupling of heat transfer,flow,stress,and chemical reaction.Revealing the coupling mechanism of flow and heat transfer inside the reservoir during geothermal exploitation can provide important theoretical support for the efficient exploitation of geothermal resources.This paper reviews the research advances of the multi-field coupling model in the reservoir during geothermal production over the past 40 years.The thrust of this paper is on objective analysis and evaluation of the importance of each coupling process and its influence on reservoir heat extraction performance.Finally,we discuss the existing challenges and perspectives to promote the future development of the geothermal reservoir multi-field coupling model.An accurate understanding of the multi-field coupling mechanism,an efficient cross-scale modeling method,as well as the accurate characterization of reservoir fracture morphology,are crucial for the multi-field coupling model of geothermal production.
基金supported by the Scientific Research Project of Beijing Municipal Education Commission,China(KM201810017004)National Key R&D Program Project of China(No.2018YFC0704800)the“Engineering and Technology R&D Center of Clean Air Conditioning in Colleges of Shandong(Shandong Huayu University of Technology).”。
文摘The increase of insulation thickness(IT)results in the decrease of the heat demand and heat medium temperature.A mathematical model on the optimum environmental insulation thickness(OEIT)for minimizing the annual total environmental impact was established based on the amount of energy and energy grade reduction.Besides,a case study was conducted based on a residential community with a combined heat and power(CHP)-based district heating system(DHS)in Tianjin,China.Moreover,the effect of IT on heat demand,heat medium temperature,exhaust heat,extracted heat,coal consumption,carbon dioxide(CO_(2))emissions and sulfur dioxide(SO_(2))emissions as well as the effect of three types of insulation materials(i.e.,expanded polystyrene,rock wool and glass wool)on the OEIT and minimum annual total environmental impact were studied.The results reveal that the optimization model can be used to determine the OEIT.When the OEIT of expanded polystyrene,rock wool and glass wool is used,the annual total environmental impact can be reduced by 84.563%,83.211%,and 86.104%,respectively.It can be found that glass wool is more beneficial to the environment compared with expanded polystyrene and rock wool.
文摘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.
