Pipe cooling is an effective method of mass concrete temperature control, but its accurate and convenient numerical simulation is still a cumbersome problem. An improved embedded model, considering the water temperatu...Pipe cooling is an effective method of mass concrete temperature control, but its accurate and convenient numerical simulation is still a cumbersome problem. An improved embedded model, considering the water temperature variation along the pipe, was proposed for simulating the temperature field of early-age concrete structures containing cooling pipes. The improved model was verified with an engineering example. Then, the p-version self-adaption algorithm for the improved embedded model was deduced, and the initial values and boundary conditions were examined. Comparison of some numerical samples shows that the proposed model can provide satisfying precision and a higher efficiency. The analysis efficiency can be doubled at the same precision, even for a large-scale element. The p-version algorithm can fit grids of different sizes for the temperature field simulation. The convenience of the proposed algorithm lies in the possibility of locating more pipe segments in one element without the need of so regular a shape as in the explicit model.展开更多
The paper addresses the problem of reconciling the modern control paradigm developed by R. Kalman in the sixties of the past century, and the centenary error-based design of the proportional, integrative and derivati...The paper addresses the problem of reconciling the modern control paradigm developed by R. Kalman in the sixties of the past century, and the centenary error-based design of the proportional, integrative and derivative （PID） controllers. This is done with the help of the error loop whose stability is proved to be necessary and sufficient for the close-loop plant stability. The error loop is built by cascading the uncertain plant-to-model discrepancies （causal, parametric, initial state, neglected dynamics）, which are driven by the design model output and by arbitrary bounded signals, with the control unit transfer functions. The embedded model control takes advantage of the error loop and its equations to design appropriate algorithms of the modern control theory （state predictor, control law, reference generator）, which guarantee the error loop stability and performance. A simulated multivariate case study shows modeling and control design steps and the coherence of the predicted and simulated performance.展开更多
Simulation of fluid flow in the fractured porous media is very important and challenging.Researchers have developed some models for fractured porous media.With the development of related research in recent years,the p...Simulation of fluid flow in the fractured porous media is very important and challenging.Researchers have developed some models for fractured porous media.With the development of related research in recent years,the prospect of embedded discrete fracture model(EDFM)is more and more bright.However,since the size of the fractures in the actual reservoir varies greatly,a very fine grid should be used which leads to a huge burden to the computing resources.To address this challenge,in the present paper,an upscaling based model is proposed.In this model,the flow in large-scale fractures is directly described by the EDFM while that in the small-scale fractures is upscaled through local simulation by EDFM.The EDFM is used to simulate the large-and small-scale fractures independently two times,so the new model is called dual embedded discrete fracture model(D-EDFM).In this paper,the detailed implementation process of D-EDFM is introduced and,through test cases,it is found the proposed model is a feasible method to simulate the flow in fractured porous media.展开更多
An embedded cell model is presented to obtain the effective elastic moduli for three-dimensional two-phase composites which is an exact analytic formula without any simplified approximation and can be expressed in an ...An embedded cell model is presented to obtain the effective elastic moduli for three-dimensional two-phase composites which is an exact analytic formula without any simplified approximation and can be expressed in an explicit form. For the different cells such as spherical inclusions and cracks surrounded by sphere and oblate ellipsoidal matrix, the effective elastic moduli are evaluated and the results are compared with those from various micromechanics models. These results show that the present model is direct, simple and efficient to deal with three-dimensional two-phase composites.展开更多
Acid fracturing is an important means of reservoir stimulation,whose purpose is to form an incompletely closed acid-etched fracture as the flow channel for oil and gas during production.The length and conductivity of ...Acid fracturing is an important means of reservoir stimulation,whose purpose is to form an incompletely closed acid-etched fracture as the flow channel for oil and gas during production.The length and conductivity of acid-etched fractures can be used to evaluate acid fracturing and directly impact production.To study their influence on the stimulation effect and final production,an acid fracturing coupling model including a fracture propagation model coupled with reservoir flow and temperature field models is established for the first time in this study based on an embedded discrete fracture model(EDFM),which can realize the coupling of fracture propagation and reservoir flow and simplify the solution of fracture and reservoir temperatures.The simulation results of the acid fracturing coupling model are introduced into the productivity model,which is also based on the EDFM to analyze and evaluate well productivity.The results show that:(1)the EDFM can easily couple fracture propagation and reservoir flow and can be used to rapidly solve the temperature fields in the fracture and reservoir successfully for the first time.(2)Reservoir flow impacts the propagation of fractures by increasing or decreasing the leak-off velocity of the working fluid.(3)Temperature diffusion is much weaker than pressure diffusion during acid fracturing and is limited near the acid fracture.The reaction between the acid and rock increases the local temperature around the acid fracture,and may even exceed the initial formation temperature.(4)Raising the injection rate reasonably enhances H^(+) diffusion,increases the effective length of acid-etched fractures,enlarges the drainage area of oil and gas,and benefits long-term well production.展开更多
In order to solve the problem that the embedded software has the shortcoming of the platform dependence, this paper presents an embedded software analysis method based on the static structure model. Before control flo...In order to solve the problem that the embedded software has the shortcoming of the platform dependence, this paper presents an embedded software analysis method based on the static structure model. Before control flow and data flow analysis, a lexical analysis/syntax analysis method with simplified grammar and sentence depth is designed to analyze the embedded software. The experiments use the open source code of smart meters as a case, and the artificial faults as the test objects, repeating 30 times. Compared with the popular static analyzing tools PC-Lint and Splint, the method can accurately orient 91% faults, which is between PC-Lint＇s 95% and Splint＇s 85%. The result indicates that the correct rate of our method is acceptable. Meanwhile, by removing the platform-dependent operation with simplified syntax analysis, our method is independent of development environment. It also shows that the method is applicable to the compiled C（including embedded software） program.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
Although human beings have come to understand and utilize coal for a very long history, no theoretical breakthrough in the study of coal structure has been made, which still needs continuous efforts of coal chemical w...Although human beings have come to understand and utilize coal for a very long history, no theoretical breakthrough in the study of coal structure has been made, which still needs continuous efforts of coal chemical workers. Based on the viewpoint of ‘vague/clear', the species classification and accurate analysis on coal were conducted by using the natural clustering all-component separation method. A more systematic and detailed coal embedded structure model theory which is suitable for coal of all ranks was developed from the previous one and a more complete theoretical system about the component and structure of coal was constructed. The whole establishment process of the theory was summarized and some of the main support data and analysis test results, including TEM, AFM, FTIR, GC/MS, MALDI/TOF/MS, DART/MSD, fractal analysis and so on were provided. The coal embedded structure theory fully considers both the identity and the particularity of all-rank coal, reflects the coal component and structure in the full range of coal rank, solves the systematic cognitive problem of coal component and structure on macro and micro level, and provides a valuable and meaningful theoretical approach for the coal processing and conversion technology.展开更多
The generation method of three-dimensional fractal discrete fracture network(FDFN)based on multiplicative cascade process was developed.The complex multi-scale fracture system in shale after fracturing was characteriz...The generation method of three-dimensional fractal discrete fracture network(FDFN)based on multiplicative cascade process was developed.The complex multi-scale fracture system in shale after fracturing was characterized by coupling the artificial fracture model and the natural fracture model.Based on an assisted history matching(AHM)using multiple-proxy-based Markov chain Monte Carlo algorithm(MCMC),an embedded discrete fracture modeling(EDFM)incorporated with reservoir simulator was used to predict productivity of shale gas well.When using the natural fracture generation method,the distribution of natural fracture network can be controlled by fractal parameters,and the natural fracture network generated coupling with artificial fractures can characterize the complex system of different-scale fractures in shale after fracturing.The EDFM,with fewer grids and less computation time consumption,can characterize the attributes of natural fractures and artificial fractures flexibly,and simulate the details of mass transfer between matrix cells and fractures while reducing computation significantly.The combination of AMH and EDFM can lower the uncertainty of reservoir and fracture parameters,and realize effective inversion of key reservoir and fracture parameters and the productivity forecast of shale gas wells.Application demonstrates the results from the proposed productivity prediction model integrating FDFN,EDFM and AHM have high credibility.展开更多
A novel and accurate method is proposed to extract the intrinsic elements of the GaN high-electron-mobility transistor（HEMT） switch.The new extraction method is verified by comparing the simulated S-parameters with ...A novel and accurate method is proposed to extract the intrinsic elements of the GaN high-electron-mobility transistor（HEMT） switch.The new extraction method is verified by comparing the simulated S-parameters with the measured data over the 5-40 GHz frequency range.The percentage errors E（ij） within 3.83% show the great agreement between the simulated S-parameters and the measured data.展开更多
In shale gas reservoir stimulation,proppants are essential for sustaining fracture conductivity.However,increasing closing stress causes proppants to embed into the rock matrix,leading to a progressive decline in frac...In shale gas reservoir stimulation,proppants are essential for sustaining fracture conductivity.However,increasing closing stress causes proppants to embed into the rock matrix,leading to a progressive decline in fracture permeability and conductivity.Furthermore,rock creep contributes to long-term reductions in fracture performance.To elucidate the combined effects of proppant embedding and rock creep on sustained conductivity,this study conducted controlled experiments examining conductivity decay in propped fractures under varying closing stresses,explicitly accounting for both mechanisms.An embedded discrete fracture model was developed to simulate reservoir production under different conductivity decay scenarios,while evaluating the influence of proppant parameters on fracture performance.The results demonstrate that fracture conductivity diminishes rapidly with increasing stress,yet at 50 MPa,the decline becomes less pronounced.Simulated production profiles show strong agreement with actual gas well data,confirming the model’s accuracy and predictive capability.These findings suggest that employing a high proppant concentration with smaller particle size(5 kg/m^(2),70/140 mesh)is effective for maintaining long-term fracture conductivity and enhancing shale gas recovery.This study provides a rigorous framework for optimizing proppant selection and designing stimulation strategies that maximize reservoir performance over time.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51109071)
文摘Pipe cooling is an effective method of mass concrete temperature control, but its accurate and convenient numerical simulation is still a cumbersome problem. An improved embedded model, considering the water temperature variation along the pipe, was proposed for simulating the temperature field of early-age concrete structures containing cooling pipes. The improved model was verified with an engineering example. Then, the p-version self-adaption algorithm for the improved embedded model was deduced, and the initial values and boundary conditions were examined. Comparison of some numerical samples shows that the proposed model can provide satisfying precision and a higher efficiency. The analysis efficiency can be doubled at the same precision, even for a large-scale element. The p-version algorithm can fit grids of different sizes for the temperature field simulation. The convenience of the proposed algorithm lies in the possibility of locating more pipe segments in one element without the need of so regular a shape as in the explicit model.
文摘The paper addresses the problem of reconciling the modern control paradigm developed by R. Kalman in the sixties of the past century, and the centenary error-based design of the proportional, integrative and derivative （PID） controllers. This is done with the help of the error loop whose stability is proved to be necessary and sufficient for the close-loop plant stability. The error loop is built by cascading the uncertain plant-to-model discrepancies （causal, parametric, initial state, neglected dynamics）, which are driven by the design model output and by arbitrary bounded signals, with the control unit transfer functions. The embedded model control takes advantage of the error loop and its equations to design appropriate algorithms of the modern control theory （state predictor, control law, reference generator）, which guarantee the error loop stability and performance. A simulated multivariate case study shows modeling and control design steps and the coherence of the predicted and simulated performance.
基金supported by National Natural Science Foundations of China(Grant Nos.51706021,51936001 and 51804033)the Beijing Youth Talent Support Program(Grant No.CIT&TCD201804037)+1 种基金Joint Project of the Beijing Natural Science Foundation and the Beijing Municipal Education Commission(Grant No.KZ201810017023)the Great Wall Scholar program(Grant No.CIT&TCD20180313).
文摘Simulation of fluid flow in the fractured porous media is very important and challenging.Researchers have developed some models for fractured porous media.With the development of related research in recent years,the prospect of embedded discrete fracture model(EDFM)is more and more bright.However,since the size of the fractures in the actual reservoir varies greatly,a very fine grid should be used which leads to a huge burden to the computing resources.To address this challenge,in the present paper,an upscaling based model is proposed.In this model,the flow in large-scale fractures is directly described by the EDFM while that in the small-scale fractures is upscaled through local simulation by EDFM.The EDFM is used to simulate the large-and small-scale fractures independently two times,so the new model is called dual embedded discrete fracture model(D-EDFM).In this paper,the detailed implementation process of D-EDFM is introduced and,through test cases,it is found the proposed model is a feasible method to simulate the flow in fractured porous media.
基金The project supported by the National Natural Science Foundation of China (No.19704100) the National Natural Science Foundation of Chinese Academy of Sciences (No. KJ951-1-201)
文摘An embedded cell model is presented to obtain the effective elastic moduli for three-dimensional two-phase composites which is an exact analytic formula without any simplified approximation and can be expressed in an explicit form. For the different cells such as spherical inclusions and cracks surrounded by sphere and oblate ellipsoidal matrix, the effective elastic moduli are evaluated and the results are compared with those from various micromechanics models. These results show that the present model is direct, simple and efficient to deal with three-dimensional two-phase composites.
基金supported by the China Postdoctoral Sci-ence Foundation(2020M683360)National Natural Science Foundation of China(U19A2043).
文摘Acid fracturing is an important means of reservoir stimulation,whose purpose is to form an incompletely closed acid-etched fracture as the flow channel for oil and gas during production.The length and conductivity of acid-etched fractures can be used to evaluate acid fracturing and directly impact production.To study their influence on the stimulation effect and final production,an acid fracturing coupling model including a fracture propagation model coupled with reservoir flow and temperature field models is established for the first time in this study based on an embedded discrete fracture model(EDFM),which can realize the coupling of fracture propagation and reservoir flow and simplify the solution of fracture and reservoir temperatures.The simulation results of the acid fracturing coupling model are introduced into the productivity model,which is also based on the EDFM to analyze and evaluate well productivity.The results show that:(1)the EDFM can easily couple fracture propagation and reservoir flow and can be used to rapidly solve the temperature fields in the fracture and reservoir successfully for the first time.(2)Reservoir flow impacts the propagation of fractures by increasing or decreasing the leak-off velocity of the working fluid.(3)Temperature diffusion is much weaker than pressure diffusion during acid fracturing and is limited near the acid fracture.The reaction between the acid and rock increases the local temperature around the acid fracture,and may even exceed the initial formation temperature.(4)Raising the injection rate reasonably enhances H^(+) diffusion,increases the effective length of acid-etched fractures,enlarges the drainage area of oil and gas,and benefits long-term well production.
基金Supported by the National Natural Science Foundation of China(61303214)the Science and Technology Project of China State Grid Corp(KJ15-1-32)
文摘In order to solve the problem that the embedded software has the shortcoming of the platform dependence, this paper presents an embedded software analysis method based on the static structure model. Before control flow and data flow analysis, a lexical analysis/syntax analysis method with simplified grammar and sentence depth is designed to analyze the embedded software. The experiments use the open source code of smart meters as a case, and the artificial faults as the test objects, repeating 30 times. Compared with the popular static analyzing tools PC-Lint and Splint, the method can accurately orient 91% faults, which is between PC-Lint＇s 95% and Splint＇s 85%. The result indicates that the correct rate of our method is acceptable. Meanwhile, by removing the platform-dependent operation with simplified syntax analysis, our method is independent of development environment. It also shows that the method is applicable to the compiled C（including embedded software） program.
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.
基金financial provided by the National Natural Science Foundation of China (Nos. 50474066, 50874108, 51274201, and 51674260)the Coal Joint Fund from National Natural Science Foundation of China and Shenhua Group Corporation Limited (No. U1361116)the National Basic Research Program of China (No. 2012CB214900)
文摘Although human beings have come to understand and utilize coal for a very long history, no theoretical breakthrough in the study of coal structure has been made, which still needs continuous efforts of coal chemical workers. Based on the viewpoint of ‘vague/clear', the species classification and accurate analysis on coal were conducted by using the natural clustering all-component separation method. A more systematic and detailed coal embedded structure model theory which is suitable for coal of all ranks was developed from the previous one and a more complete theoretical system about the component and structure of coal was constructed. The whole establishment process of the theory was summarized and some of the main support data and analysis test results, including TEM, AFM, FTIR, GC/MS, MALDI/TOF/MS, DART/MSD, fractal analysis and so on were provided. The coal embedded structure theory fully considers both the identity and the particularity of all-rank coal, reflects the coal component and structure in the full range of coal rank, solves the systematic cognitive problem of coal component and structure on macro and micro level, and provides a valuable and meaningful theoretical approach for the coal processing and conversion technology.
基金Supported by the National Science and Technology Major Project(2017ZX05063-005)Science and Technology Development Project of PetroChina Research Institute of Petroleum Exploration and Development(YGJ2019-12-04)。
文摘The generation method of three-dimensional fractal discrete fracture network(FDFN)based on multiplicative cascade process was developed.The complex multi-scale fracture system in shale after fracturing was characterized by coupling the artificial fracture model and the natural fracture model.Based on an assisted history matching(AHM)using multiple-proxy-based Markov chain Monte Carlo algorithm(MCMC),an embedded discrete fracture modeling(EDFM)incorporated with reservoir simulator was used to predict productivity of shale gas well.When using the natural fracture generation method,the distribution of natural fracture network can be controlled by fractal parameters,and the natural fracture network generated coupling with artificial fractures can characterize the complex system of different-scale fractures in shale after fracturing.The EDFM,with fewer grids and less computation time consumption,can characterize the attributes of natural fractures and artificial fractures flexibly,and simulate the details of mass transfer between matrix cells and fractures while reducing computation significantly.The combination of AMH and EDFM can lower the uncertainty of reservoir and fracture parameters,and realize effective inversion of key reservoir and fracture parameters and the productivity forecast of shale gas wells.Application demonstrates the results from the proposed productivity prediction model integrating FDFN,EDFM and AHM have high credibility.
文摘A novel and accurate method is proposed to extract the intrinsic elements of the GaN high-electron-mobility transistor（HEMT） switch.The new extraction method is verified by comparing the simulated S-parameters with the measured data over the 5-40 GHz frequency range.The percentage errors E（ij） within 3.83% show the great agreement between the simulated S-parameters and the measured data.
基金supported by the National Natural Science Foundation of China(Nos.52204051,52304046).
文摘In shale gas reservoir stimulation,proppants are essential for sustaining fracture conductivity.However,increasing closing stress causes proppants to embed into the rock matrix,leading to a progressive decline in fracture permeability and conductivity.Furthermore,rock creep contributes to long-term reductions in fracture performance.To elucidate the combined effects of proppant embedding and rock creep on sustained conductivity,this study conducted controlled experiments examining conductivity decay in propped fractures under varying closing stresses,explicitly accounting for both mechanisms.An embedded discrete fracture model was developed to simulate reservoir production under different conductivity decay scenarios,while evaluating the influence of proppant parameters on fracture performance.The results demonstrate that fracture conductivity diminishes rapidly with increasing stress,yet at 50 MPa,the decline becomes less pronounced.Simulated production profiles show strong agreement with actual gas well data,confirming the model’s accuracy and predictive capability.These findings suggest that employing a high proppant concentration with smaller particle size(5 kg/m^(2),70/140 mesh)is effective for maintaining long-term fracture conductivity and enhancing shale gas recovery.This study provides a rigorous framework for optimizing proppant selection and designing stimulation strategies that maximize reservoir performance over time.
