The utilization of coalbed methane(CBM)cannot only alleviate the energy crisis,but also reduce greenhouse gas emissions.Gas injection is an effective method to enhance CBM recovery.Compared to single-gas injection,the...The utilization of coalbed methane(CBM)cannot only alleviate the energy crisis,but also reduce greenhouse gas emissions.Gas injection is an effective method to enhance CBM recovery.Compared to single-gas injection,the injection of CO_(2)/N_(2) mixtures can balance the sharp decline in permeability caused by pure CO_(2) and the premature breakthrough by pure N_(2).In this study,a more comprehensive thermo-hydro-mechanical(THM)coupled mathematical model was developed,incorporating processes such as ternary gas non-isothermal adsorption,gas dissolution in water,gas-water two-phase flow,energy exchange,and coal deformation.After experimental validation,the model was applied to simulate the entire process of gas mixtures for enhanced CBM recovery(GM-ECBM).Results indicate that the permeability near the production well(Pw)initially decreases due to increased effective stress,then increases as a result of CH_(4) desorption.Near the injection well(Iw),the permeability first increases due to reduced effective stress and later stabilizes under the combined effects of effective stress and CO_(2)/N_(2) adsorption.The initial CH_(4) pressure and coal seam permeability have the most significant impact on CH_(4) production,while the coal seam permeability and temperature significantly affect CO_(2)/N_(2) injection.As the coal seam permeability increases,the optimal CO_(2)/N_(2) ratio also increases accordingly.These findings provide important theoretical guidance for improving GM-ECBM efficiency in coal seams with varying permeabilities.展开更多
In examining potential host rocks for such purposes as the disposal of high-level radioactive wastes,it is important to understand the coupled thermo-hydro-mechanical（THM） behavior of a porous medium.A rigorous and ...In examining potential host rocks for such purposes as the disposal of high-level radioactive wastes,it is important to understand the coupled thermo-hydro-mechanical（THM） behavior of a porous medium.A rigorous and fully unified coupled thermo-hydro-mechanical model for unsaturated porous media is required to simulate the complex coupling mechanisms involved.Based on modified Darcy＇s and Fourier＇s laws,equations of mechanical equilibrium,mass conservation and energy conservation are derived by introducing void ratio and volumetric liquid water content into the model.The newly derived model takes into account the effects of temperature on the dynamic viscosity of liquid water and void ratio,the influence of liquid flow on temperature gradient（thermo-osmosis）,the influence on mass and heat conservation equations,and the influence of heat flow on water pressure gradient and thermal convection.The new coupled THM constitutive model is constructed by a finite element program and is used to simulate the coupled behavior of a tunnel during excavation,ventilation and concrete lining stages.Oil and gas engineering,underground disposal of nuclear waste and tunnel engineering may be benefited from the development of the new model.展开更多
The permeability contrast between the Hot Dry Rock(HDR)reservoir and the surrounding formations is a key factor governing fluid loss in Enhanced Geothermal Systems(EGS).This study thus aims to investigate its impact o...The permeability contrast between the Hot Dry Rock(HDR)reservoir and the surrounding formations is a key factor governing fluid loss in Enhanced Geothermal Systems(EGS).This study thus aims to investigate its impact on system performance under varying operating conditions,and a three-dimensional thermo–hydro–mechanical(THM)coupled EGS model is developed based on the geological parameters of the GR1 well in the Qiabuqia region.The coupled processes of fluid flow,heat transfer,and geomechanics within the reservoir under varying reservoir–surrounding rock permeability contrasts,as well as the flow and heat exchange along the wellbores fromthe reservoir to the surface are simulated.Then,the influence of permeability contrast,production pressure,injection rate,and injection temperature on fluid loss and heat extraction performance over a 35-year operation period is quantitatively assessed.Theresults show that increasing the permeability contrast effectively suppresses fluid loss and enhances early-stage heat production,but also accelerates thermal breakthrough and shortens the stable operation period.When the contrast rises from 1×10^(3) to 1×10^(5),the cumulative fluid loss rate drops from 54.34%to 0.23%,and the total heat production increases by 132%,although the breakthrough occurs 5 years earlier.Meanwhile,higher production pressure delays thermal breakthrough and slows transient temperature decline,but exacerbates fluid loss and reduces heat production power.For instance,raising the pressure from 17 to 21 MPa increases the fluid loss rate from 33.17%to 54.34%and reduces average annual heat production power from 25.43 to 14.59MWth.In addition,increasing the injection rate(46 to 66 kg/s)lowers fluid loss rate but brings forward thermal breakthrough by 9 years and causes a 41 K temperature drop at the end of operation.Notably,under high fluid loss,the dynamic response pattern of heat production power shifts from a temperature-dominated“stable–breakthrough–decline”mode to a novel“rising–breakthrough–decline”mode jointly governed by both production temperature and flow rates.These findings provide theoretical support and engineering guidance for improving EGS performance.展开更多
In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)...In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical(THM)coupling processes for heat extraction in geothermal reservoir.We further employed the model on the Habanero enhanced geothermal systems(EGS)project located in Australia.First,our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations,as well as uneven spatial distribution of shear failure in 3D fracture networks.Activated shear failure is mainly concentrated in the first fracture cluster.Secondly,channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal stresses.Moreover,the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and temperature.The NR-DFN model framework and the Habanero EGS's results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.展开更多
In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well...In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well (IW) and CH_(4) production well (PW) are established, aiming to explore the behavior of free gases after CO_(2) is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH4 or CO2 content in the shale fractures/matrix is invariably heterogeneous. The CO_(2) involvement facilitates the ratio of free CH_(4)/CO_(2) in the matrix to that in the fractures declines and tends to be stable with time. Different combinations of IW–PWs induce a difference in the ratio of the free CH4 to the free CO_(2), in the ratio of the free CH_(4)/CO_(2) in the matrix to that in the fractures, in the content of the recovered free CH_(4), and in the content of the trapped free CO_(2). Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO2 in the free phase to be trapped;furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH_(4) in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO_(2) injection technique.展开更多
Reducing greenhouse gas emissions and improving unconventional gas recovery are pressing challenges worldwide.This study investigates the leading role of coal permeability in CO_(2)-enhanced coalbed methane recovery(C...Reducing greenhouse gas emissions and improving unconventional gas recovery are pressing challenges worldwide.This study investigates the leading role of coal permeability in CO_(2)-enhanced coalbed methane recovery(CO_(2)-ECBM)using an improved thermo-hydro-mechanical(THM)coupling model.The model is validated and applied to the simulation of CO_(2)-ECBM process under varying permeability.The direct positive relationship between both cumulative CH_(4)production and cumulative CO_(2)injection with coal permeability,and operating duration of CO_(2)-ECBM is negatively correlated with coal permeability.The delay in the injection start time will extend the operating duration of CO_(2)-ECBM and overcome the problem of early CO_(2)breakthrough.An increase in both delayed start time for injection and coal permeability progressively boosts CH_(4)production,while diminishing CO_(2)sequestration.The optimal start timing for CO_(2)injection is contingent upon primary objectives,such as CO_(2)sequestration or CH_(4)production.For the primary constraint of CO_(2)sequestration,the optimal starting time should be before the peak gas production.For the primary constraint of CH_(4)production,the optimal starting time should be after the peak gas production.In analyzed instances,the optimal timing for CO_(2)injection exhibits an inverse correlation with coal permeability.The results provide practical insights for CO_(2)injection optimization and field applications.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52174117)the Universitylocal Government Scientific and Technical Cooperation Cultivation Project of Ordos Institute-LNTU(Grant No.YJY-XD-2024-A-009)+2 种基金the Basic Scientific Research Project of Liaoning Provincial Department of Education(Grant No.JYTZD2023073)the Liaoning Revitalization Talents Program(XLYC2203139)the Liaoning Provincial Natural Science Foundation Program(Excellent Youth Fund)(Grant No.2024JH3/10200043).
文摘The utilization of coalbed methane(CBM)cannot only alleviate the energy crisis,but also reduce greenhouse gas emissions.Gas injection is an effective method to enhance CBM recovery.Compared to single-gas injection,the injection of CO_(2)/N_(2) mixtures can balance the sharp decline in permeability caused by pure CO_(2) and the premature breakthrough by pure N_(2).In this study,a more comprehensive thermo-hydro-mechanical(THM)coupled mathematical model was developed,incorporating processes such as ternary gas non-isothermal adsorption,gas dissolution in water,gas-water two-phase flow,energy exchange,and coal deformation.After experimental validation,the model was applied to simulate the entire process of gas mixtures for enhanced CBM recovery(GM-ECBM).Results indicate that the permeability near the production well(Pw)initially decreases due to increased effective stress,then increases as a result of CH_(4) desorption.Near the injection well(Iw),the permeability first increases due to reduced effective stress and later stabilizes under the combined effects of effective stress and CO_(2)/N_(2) adsorption.The initial CH_(4) pressure and coal seam permeability have the most significant impact on CH_(4) production,while the coal seam permeability and temperature significantly affect CO_(2)/N_(2) injection.As the coal seam permeability increases,the optimal CO_(2)/N_(2) ratio also increases accordingly.These findings provide important theoretical guidance for improving GM-ECBM efficiency in coal seams with varying permeabilities.
基金Supported by the National Natural Science Foundation of China (50579087,50720135906, 50539050)CAS/SAFEA International Partnership Program for Creative Research Teams
文摘In examining potential host rocks for such purposes as the disposal of high-level radioactive wastes,it is important to understand the coupled thermo-hydro-mechanical（THM） behavior of a porous medium.A rigorous and fully unified coupled thermo-hydro-mechanical model for unsaturated porous media is required to simulate the complex coupling mechanisms involved.Based on modified Darcy＇s and Fourier＇s laws,equations of mechanical equilibrium,mass conservation and energy conservation are derived by introducing void ratio and volumetric liquid water content into the model.The newly derived model takes into account the effects of temperature on the dynamic viscosity of liquid water and void ratio,the influence of liquid flow on temperature gradient（thermo-osmosis）,the influence on mass and heat conservation equations,and the influence of heat flow on water pressure gradient and thermal convection.The new coupled THM constitutive model is constructed by a finite element program and is used to simulate the coupled behavior of a tunnel during excavation,ventilation and concrete lining stages.Oil and gas engineering,underground disposal of nuclear waste and tunnel engineering may be benefited from the development of the new model.
基金supported by the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation(GZC20251944)the National Natural Science Foundation of China(No.52376044)the National Key Research and Development Program of China(2024YFE0100800).
文摘The permeability contrast between the Hot Dry Rock(HDR)reservoir and the surrounding formations is a key factor governing fluid loss in Enhanced Geothermal Systems(EGS).This study thus aims to investigate its impact on system performance under varying operating conditions,and a three-dimensional thermo–hydro–mechanical(THM)coupled EGS model is developed based on the geological parameters of the GR1 well in the Qiabuqia region.The coupled processes of fluid flow,heat transfer,and geomechanics within the reservoir under varying reservoir–surrounding rock permeability contrasts,as well as the flow and heat exchange along the wellbores fromthe reservoir to the surface are simulated.Then,the influence of permeability contrast,production pressure,injection rate,and injection temperature on fluid loss and heat extraction performance over a 35-year operation period is quantitatively assessed.Theresults show that increasing the permeability contrast effectively suppresses fluid loss and enhances early-stage heat production,but also accelerates thermal breakthrough and shortens the stable operation period.When the contrast rises from 1×10^(3) to 1×10^(5),the cumulative fluid loss rate drops from 54.34%to 0.23%,and the total heat production increases by 132%,although the breakthrough occurs 5 years earlier.Meanwhile,higher production pressure delays thermal breakthrough and slows transient temperature decline,but exacerbates fluid loss and reduces heat production power.For instance,raising the pressure from 17 to 21 MPa increases the fluid loss rate from 33.17%to 54.34%and reduces average annual heat production power from 25.43 to 14.59MWth.In addition,increasing the injection rate(46 to 66 kg/s)lowers fluid loss rate but brings forward thermal breakthrough by 9 years and causes a 41 K temperature drop at the end of operation.Notably,under high fluid loss,the dynamic response pattern of heat production power shifts from a temperature-dominated“stable–breakthrough–decline”mode to a novel“rising–breakthrough–decline”mode jointly governed by both production temperature and flow rates.These findings provide theoretical support and engineering guidance for improving EGS performance.
基金funded by the National Natural Science Foundation of China (No.U22A20166)Science and Technology Foundation of Guizhou Province (No.QKHJC-ZK[2023]YB074)+2 种基金Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical EngineeringInstitute of Rock and Soil MechanicsChinese Academy of Sciences (No.SKLGME022009)。
文摘In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical(THM)coupling processes for heat extraction in geothermal reservoir.We further employed the model on the Habanero enhanced geothermal systems(EGS)project located in Australia.First,our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations,as well as uneven spatial distribution of shear failure in 3D fracture networks.Activated shear failure is mainly concentrated in the first fracture cluster.Secondly,channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal stresses.Moreover,the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and temperature.The NR-DFN model framework and the Habanero EGS's results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.
基金This study was financially supported by the National Natural Science Foundation of China(Grant Nos.51704197 and 11872258)。
文摘In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well (IW) and CH_(4) production well (PW) are established, aiming to explore the behavior of free gases after CO_(2) is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH4 or CO2 content in the shale fractures/matrix is invariably heterogeneous. The CO_(2) involvement facilitates the ratio of free CH_(4)/CO_(2) in the matrix to that in the fractures declines and tends to be stable with time. Different combinations of IW–PWs induce a difference in the ratio of the free CH4 to the free CO_(2), in the ratio of the free CH_(4)/CO_(2) in the matrix to that in the fractures, in the content of the recovered free CH_(4), and in the content of the trapped free CO_(2). Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO2 in the free phase to be trapped;furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH_(4) in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO_(2) injection technique.
基金supported by the National Natural Science Foundation of China(52174117)Liaoning Province Doctoral Youth Seedling Project(LJ212510147007)+3 种基金the University-local government scientific and technical cooperation cultivation project of Ordos Institute-LNTU(YJY-XD-2024-A-009)the Basic scientific research project of Liaoning Provincial Department of Education(JYTZD2023073)the Liaoning Revitalization Talents Program(XLYC2203139)the Liaoning Provincial Natural Science Foundation Program(Excellent Youth Fund)(2024JH3/10200043).
文摘Reducing greenhouse gas emissions and improving unconventional gas recovery are pressing challenges worldwide.This study investigates the leading role of coal permeability in CO_(2)-enhanced coalbed methane recovery(CO_(2)-ECBM)using an improved thermo-hydro-mechanical(THM)coupling model.The model is validated and applied to the simulation of CO_(2)-ECBM process under varying permeability.The direct positive relationship between both cumulative CH_(4)production and cumulative CO_(2)injection with coal permeability,and operating duration of CO_(2)-ECBM is negatively correlated with coal permeability.The delay in the injection start time will extend the operating duration of CO_(2)-ECBM and overcome the problem of early CO_(2)breakthrough.An increase in both delayed start time for injection and coal permeability progressively boosts CH_(4)production,while diminishing CO_(2)sequestration.The optimal start timing for CO_(2)injection is contingent upon primary objectives,such as CO_(2)sequestration or CH_(4)production.For the primary constraint of CO_(2)sequestration,the optimal starting time should be before the peak gas production.For the primary constraint of CH_(4)production,the optimal starting time should be after the peak gas production.In analyzed instances,the optimal timing for CO_(2)injection exhibits an inverse correlation with coal permeability.The results provide practical insights for CO_(2)injection optimization and field applications.
