为了探究Klinkenberg效应及不同状态的Klinkenberg因子在注CO_(2)提高煤层气采收率(CO_(2)-Enhanced Coal Bed Methane,CO_(2)-ECBM)过程中的作用,借助COMSOL有限元软件模拟分析了Klinkenberg因子为0、固定Klinkenberg因子与动态Klinken...为了探究Klinkenberg效应及不同状态的Klinkenberg因子在注CO_(2)提高煤层气采收率(CO_(2)-Enhanced Coal Bed Methane,CO_(2)-ECBM)过程中的作用,借助COMSOL有限元软件模拟分析了Klinkenberg因子为0、固定Klinkenberg因子与动态Klinkenberg因子3种状态对CO_(2)-ECBM及有效渗透率的影响,以及CH_(4)与CO_(2)压力随该因子的动态变化情况,并将CH_(4)产气量与工程实际作了对比验证。结果表明,CH_(4)与CO_(2)有效渗透率呈先缓慢增长再急速下降后逐渐趋于平缓的态势,相较于固定Klinkenberg因子或Klinkenberg因子为0,动态Klinkenberg因子影响下的CH_(4)与CO_(2)有效渗透率更大,当Klinkenberg因子为动态变量时,受不同气体的摩尔质量与动力黏度影响,CO_(2)有效渗透率小于CH_(4)有效渗透率。在动态Klinkenberg因子作用下,煤层中CH_(4)压力下降和CO_(2)压力上升均更快,当Klinkenberg因子为固定值或0时,会高估煤层内CH_(4)压力,低估CH_(4)抽采与CO_(2)压注的影响范围,并且估值均随时间增长而增大。工程验证表明,考虑动态Klinkenberg因子作用下的CH_(4)累积产气量更接近真实情况。研究成果有助于分析CH_(4)与CO_(2)有效渗透率变化趋势,预估CH_(4)抽采与CO_(2)压注的影响范围及CH_(4)产气量,在探究煤层增渗,优化井网布置,定量评价煤田产气量等方面具有理论指导意义。展开更多
Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are...Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are taken as research objects.Firstly,visualization reconstruction of coal reservoir is realized.Secondly,the evolution of the pore/fracture structures under different swelling contents is discussed.Then,the influence of matrix phase with different swelling contents on permeability is discussed.Finally,the mechanism of swelling effect during the CO_(2)-ECBM process is further discussed.The results show that the intra-matrix pores and matrix-edge fractures are the focus of this study,and the contacting area between matrix and pore/fracture is the core area of matrix swelling.The number of matrix particles decreases with the increase of size,and the distribution of which is isolated with small size and interconnected with large size.The swelling effect of matrix particles with larger size has a great influence on the pore/fracture structures.The number of connected pores/fractures is limited and only interconnected in a certain direction.With the increase of matrix swelling content,the number,porosity,width,fractal dimension,surface area and volume of pores/fractures decrease,and their negative contribution to absolute permeability increases from 0.368% to 0.633% and 0.868%-1.404%,respectively.With the increase of swelling content,the number of intra-matrix pores gradually decreases and the pore radius becomes shorter during the CO_(2)-ECBM process.The matrix continuously expands to the connected fractures,and the width of connected fractures gradually shorten.Under the influence of matrix swelling,the bending degree of fluid flow increases gradually,so the resistance of fluid migration increases and the permeability gradually decreases.This study shows that the matrix swelling effect is the key factor affecting CBM recovery,and the application of this effect in CO_(2)-ECBM process can be discussed.展开更多
The technology used to enhance coalbed methane(CBM) recovery by injecting CO_2(CO_2-ECBM) with heat, combining heat injection with CO_2 injection, is still in its infancy; therefore, theoretical studies of this CO_2-E...The technology used to enhance coalbed methane(CBM) recovery by injecting CO_2(CO_2-ECBM) with heat, combining heat injection with CO_2 injection, is still in its infancy; therefore, theoretical studies of this CO_2-ECBM technology should be perused. First, the coupling equations of the di usion–adsorption–seepage–heat transfer fields of gas are established. The displacement processes under di erent pressures and temperatures are simulated by COMSOL. Finally, the displacement effects, a comparison of the CO_2 storage capacity with the CH_4 output and the e ective influencing radius of CO_2 injection are analyzed and discussed. The results show that(1) the displacement pressure and temperature are two key factors influencing the CH_4 output and the CO_2 storage capacity, and the increase in the CO_2 storage capacity is more sensitive to temperature and pressure than the CH_4 output.(2) The gas flow direction is from the injection hole to the discharge hole during the displacement process, and the regions with high velocity are concentrated at the injection hole and the discharge hole.(3) A reduction in the CH_4 concentration and an increase in the CO_2 concentration are obvious during the displacement process.(4) The e ective influencing radius of injecting CO_2 with heat increases with the increase in time and pressure. The relationship between the e ective influencing radius and the injection time of CO_2 has a power exponential function, and there is a linear relationship between the functional coe cient and the injection pressure of CO_2. This numerical simulation study on enhancing CBM recovery by injecting CO_2 with heat can further promote the implementation of CO_2-ECBM project in deep coal seams.展开更多
Sequestration of carbon dioxide（CO<sub>2</sub>） in deep, unminable coalseam is an innovative technology, because it can not only reduce greenhouse gas in the atmosphere,but also enhance coalbed methane r...Sequestration of carbon dioxide（CO<sub>2</sub>） in deep, unminable coalseam is an innovative technology, because it can not only reduce greenhouse gas in the atmosphere,but also enhance coalbed methane recovery（CO<sub>2</sub>-ECBM）.Lots of research have been carried out on this topic in recent years.However,few of them were focused on the comparison of the展开更多
Deep coal seams are one of the world’s most widespread deposits for carbon dioxide(C02)disposal and are generally located near large point sources of CO_(2)emissions.The injection of CO_(2)into coal seams has great p...Deep coal seams are one of the world’s most widespread deposits for carbon dioxide(C02)disposal and are generally located near large point sources of CO_(2)emissions.The injection of CO_(2)into coal seams has great potential to sequester CO_(2)while simultaneously enhancing coalbed methane(CO_(2)-ECBM)recovery.Pilot tests of CO_(2)-ECBM have been conducted in coal seams worldwide with favorable early results.However,one of the main technical barriers in coal seams needs to be resolved:Injecting CO_(2)reduces coal permeability and well injectivity.Here,using in situ synchrotron X-ray microtomography,we provide the first observational evidence that injecting nitrogen(N_(2))can reverse much of this lost permeability by reopening fractures that have closed due to coal swelling induced by CO_(2)adsorption.Our findings support the notion that injecting minimally treated flue gas-a mixture of mainly N_(2) and CO_(2)-is an attractive alternative for ECBM recovery instead of pure CO_(2)injection in deep coal seams.Firstly,flue gas produced by power plants could be directly injected after particulate removal,thus avoiding high CO_(2)-separation costs.Secondly,the presence of N_(2)makes it possible to maintain a sufficiently high level of coal permeability.These results suggest that flue-gas ECBM for deep coal seams may provide a promising path toward net-zero emissions from coal mines.展开更多
The permeability and its horizontal anisotropy induce a critical influence on staged CH_(4) output inhibition process.However,a quantitative evaluation of this influence has been rarely reported in the literature.In t...The permeability and its horizontal anisotropy induce a critical influence on staged CH_(4) output inhibition process.However,a quantitative evaluation of this influence has been rarely reported in the literature.In this work,the impact of horizontal anisotropic permeability on CO_(2)-ECBM was numerically investigated.The variation in the staged CH_(4) output inhibition was analyzed.The ideal displacement profile of the CO_(2)-ECBM process was established for the first time.Moreover,the variation in CH_(4) output of different wellbores was discussed.The results showed that 1)low-permeable or weak-anisotropic reservoirs were not conducive to enhanced CH_(4) recovery owing to long inhibition time(>1091 days)and high inhibition level(>36.9%).As permeability and anisotropy increased,due to the accelerated seepage of free water,the hysteresis time and inhibition time could decrease to as short as 5 days and 87 days,respectively,and the inhibition level could weaken to as low as 5.00%.Additionally,the CH_(4) output and CO_(2) injection could increase significantly.2)Nevertheless,high permeability and strong anisotropy easily induced CO_(2) breakthrough,resulting in lower CH_(4) production,CO_(2) injection and CO_(2) storage than expected.While maintaining high efficiency of CO_(2) storage(>99%),upregulating CO_(2) breakthrough concentration from 10%to 20%might ease the unfavorable trend.3)Along the direction of fluid flow,the ideal displacement profile consisted of CO_(2) enriched bank,CO_(2) and CH_(4) mixed bank,CH_(4) enriched bank,and water enriched bank,whereas a remarkable gap in the displacement profiles of the dominant and non-dominant seepage directions was observed.4)The potential of CH_(4) output might vary greatly among different wellbores.The producers along the dominant seepage direction held more potential for CH_(4) recovery in the short-term,while those along the non-dominant seepage direction avoided becoming invalid only if a long-time injection measure was taken for the injectors.These findings pave the way to understand fluid seepage in real complex reservoirs during CO_(2)-ECBM and conduct further field projects.展开更多
Three-dimensional(3D)reconstruction of the equivalent pore network model(PNM)using X-ray computed tomography(CT)data are of significance for studying the CO_(2)-enhanced coalbed methane recovery(CO_(2)-ECBM).The docki...Three-dimensional(3D)reconstruction of the equivalent pore network model(PNM)using X-ray computed tomography(CT)data are of significance for studying the CO_(2)-enhanced coalbed methane recovery(CO_(2)-ECBM).The docking among X-ray CT technology,MATLAB,with COMSOL software not only can realize the 3D reconstruction of PNM,but also the CO_(2)-ECBM process simulation.The results show that the Median filtering algorithm enabled the de-noising of the original 2D CT slices,the image segmentation of all slices was realized based on the selected threshold,and the PNM can be constructed based on the Maximum Sphere algorithm.The mathematical model of CO_(2)-ECBM process fully coupled the expanded Langmuir equation.At the same time for CO_(2)injection,CH_(4)pressure tends to decrease with the increase of CO_(2)pressure,but its difference is not obvious.The CH_(4)pressure in the slice center changed a lot,while at the edge it changed a little under different CO_(2)pressures.The injected CO_(2)was transported to matrix along the macro and micro-fractures with continuous flow.The injected CO_(2)first replaced the adsorbed CH_(4)by covering the inner surface of macro-pores and meso-pores to form the single molecular layer adsorption of CO_(2).Then they migrated to micro-pores by Fick’s diffusion,sliding flow,and surface diffusion.Furthermore,the CO_(2)replaced CH_(4)adsorbed by volumetric filling in micro-pores,and formed the multi-molecular layer adsorption of CO_(2).The gas pressure and migration path between CO_(2)and CH_(4)are opposite.This study can provide a theoretical basis for studying digital rock physics technology and enrich the development of CO_(2)-ECBM technology.展开更多
文摘为了探究Klinkenberg效应及不同状态的Klinkenberg因子在注CO_(2)提高煤层气采收率(CO_(2)-Enhanced Coal Bed Methane,CO_(2)-ECBM)过程中的作用,借助COMSOL有限元软件模拟分析了Klinkenberg因子为0、固定Klinkenberg因子与动态Klinkenberg因子3种状态对CO_(2)-ECBM及有效渗透率的影响,以及CH_(4)与CO_(2)压力随该因子的动态变化情况,并将CH_(4)产气量与工程实际作了对比验证。结果表明,CH_(4)与CO_(2)有效渗透率呈先缓慢增长再急速下降后逐渐趋于平缓的态势,相较于固定Klinkenberg因子或Klinkenberg因子为0,动态Klinkenberg因子影响下的CH_(4)与CO_(2)有效渗透率更大,当Klinkenberg因子为动态变量时,受不同气体的摩尔质量与动力黏度影响,CO_(2)有效渗透率小于CH_(4)有效渗透率。在动态Klinkenberg因子作用下,煤层中CH_(4)压力下降和CO_(2)压力上升均更快,当Klinkenberg因子为固定值或0时,会高估煤层内CH_(4)压力,低估CH_(4)抽采与CO_(2)压注的影响范围,并且估值均随时间增长而增大。工程验证表明,考虑动态Klinkenberg因子作用下的CH_(4)累积产气量更接近真实情况。研究成果有助于分析CH_(4)与CO_(2)有效渗透率变化趋势,预估CH_(4)抽采与CO_(2)压注的影响范围及CH_(4)产气量,在探究煤层增渗,优化井网布置,定量评价煤田产气量等方面具有理论指导意义。
基金This work was financially supported by the National Natural Science Foundation of China(No.42102217)the University Synergy Innovation Program of Anhui Province(No.GXXT-2021-018)+3 种基金the Natural Science Research Project of Anhui University(No.KJ2020A0315No.KJ2020A0317)the Natural Science Foundation of Anhui Province(No.2108085MD134)the Foundation of State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing(No.PRP/open-2005).
文摘Matrix swelling effect will cause the change of microstructure of coal reservoir and its permeability,which is the key factor affecting the engineering effect of CO_(2)-ECBM technology.The Sihe and Yuwu collieries are taken as research objects.Firstly,visualization reconstruction of coal reservoir is realized.Secondly,the evolution of the pore/fracture structures under different swelling contents is discussed.Then,the influence of matrix phase with different swelling contents on permeability is discussed.Finally,the mechanism of swelling effect during the CO_(2)-ECBM process is further discussed.The results show that the intra-matrix pores and matrix-edge fractures are the focus of this study,and the contacting area between matrix and pore/fracture is the core area of matrix swelling.The number of matrix particles decreases with the increase of size,and the distribution of which is isolated with small size and interconnected with large size.The swelling effect of matrix particles with larger size has a great influence on the pore/fracture structures.The number of connected pores/fractures is limited and only interconnected in a certain direction.With the increase of matrix swelling content,the number,porosity,width,fractal dimension,surface area and volume of pores/fractures decrease,and their negative contribution to absolute permeability increases from 0.368% to 0.633% and 0.868%-1.404%,respectively.With the increase of swelling content,the number of intra-matrix pores gradually decreases and the pore radius becomes shorter during the CO_(2)-ECBM process.The matrix continuously expands to the connected fractures,and the width of connected fractures gradually shorten.Under the influence of matrix swelling,the bending degree of fluid flow increases gradually,so the resistance of fluid migration increases and the permeability gradually decreases.This study shows that the matrix swelling effect is the key factor affecting CBM recovery,and the application of this effect in CO_(2)-ECBM process can be discussed.
基金financially supported by the National Natural Science Foundation of China(No.41330638)
文摘The technology used to enhance coalbed methane(CBM) recovery by injecting CO_2(CO_2-ECBM) with heat, combining heat injection with CO_2 injection, is still in its infancy; therefore, theoretical studies of this CO_2-ECBM technology should be perused. First, the coupling equations of the di usion–adsorption–seepage–heat transfer fields of gas are established. The displacement processes under di erent pressures and temperatures are simulated by COMSOL. Finally, the displacement effects, a comparison of the CO_2 storage capacity with the CH_4 output and the e ective influencing radius of CO_2 injection are analyzed and discussed. The results show that(1) the displacement pressure and temperature are two key factors influencing the CH_4 output and the CO_2 storage capacity, and the increase in the CO_2 storage capacity is more sensitive to temperature and pressure than the CH_4 output.(2) The gas flow direction is from the injection hole to the discharge hole during the displacement process, and the regions with high velocity are concentrated at the injection hole and the discharge hole.(3) A reduction in the CH_4 concentration and an increase in the CO_2 concentration are obvious during the displacement process.(4) The e ective influencing radius of injecting CO_2 with heat increases with the increase in time and pressure. The relationship between the e ective influencing radius and the injection time of CO_2 has a power exponential function, and there is a linear relationship between the functional coe cient and the injection pressure of CO_2. This numerical simulation study on enhancing CBM recovery by injecting CO_2 with heat can further promote the implementation of CO_2-ECBM project in deep coal seams.
文摘Sequestration of carbon dioxide（CO<sub>2</sub>） in deep, unminable coalseam is an innovative technology, because it can not only reduce greenhouse gas in the atmosphere,but also enhance coalbed methane recovery（CO<sub>2</sub>-ECBM）.Lots of research have been carried out on this topic in recent years.However,few of them were focused on the comparison of the
文摘Deep coal seams are one of the world’s most widespread deposits for carbon dioxide(C02)disposal and are generally located near large point sources of CO_(2)emissions.The injection of CO_(2)into coal seams has great potential to sequester CO_(2)while simultaneously enhancing coalbed methane(CO_(2)-ECBM)recovery.Pilot tests of CO_(2)-ECBM have been conducted in coal seams worldwide with favorable early results.However,one of the main technical barriers in coal seams needs to be resolved:Injecting CO_(2)reduces coal permeability and well injectivity.Here,using in situ synchrotron X-ray microtomography,we provide the first observational evidence that injecting nitrogen(N_(2))can reverse much of this lost permeability by reopening fractures that have closed due to coal swelling induced by CO_(2)adsorption.Our findings support the notion that injecting minimally treated flue gas-a mixture of mainly N_(2) and CO_(2)-is an attractive alternative for ECBM recovery instead of pure CO_(2)injection in deep coal seams.Firstly,flue gas produced by power plants could be directly injected after particulate removal,thus avoiding high CO_(2)-separation costs.Secondly,the presence of N_(2)makes it possible to maintain a sufficiently high level of coal permeability.These results suggest that flue-gas ECBM for deep coal seams may provide a promising path toward net-zero emissions from coal mines.
基金the National Natural Science Foundation of China(Grant No.42141012)the National Key R&D Program of China(No.2018YFB0605600)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘The permeability and its horizontal anisotropy induce a critical influence on staged CH_(4) output inhibition process.However,a quantitative evaluation of this influence has been rarely reported in the literature.In this work,the impact of horizontal anisotropic permeability on CO_(2)-ECBM was numerically investigated.The variation in the staged CH_(4) output inhibition was analyzed.The ideal displacement profile of the CO_(2)-ECBM process was established for the first time.Moreover,the variation in CH_(4) output of different wellbores was discussed.The results showed that 1)low-permeable or weak-anisotropic reservoirs were not conducive to enhanced CH_(4) recovery owing to long inhibition time(>1091 days)and high inhibition level(>36.9%).As permeability and anisotropy increased,due to the accelerated seepage of free water,the hysteresis time and inhibition time could decrease to as short as 5 days and 87 days,respectively,and the inhibition level could weaken to as low as 5.00%.Additionally,the CH_(4) output and CO_(2) injection could increase significantly.2)Nevertheless,high permeability and strong anisotropy easily induced CO_(2) breakthrough,resulting in lower CH_(4) production,CO_(2) injection and CO_(2) storage than expected.While maintaining high efficiency of CO_(2) storage(>99%),upregulating CO_(2) breakthrough concentration from 10%to 20%might ease the unfavorable trend.3)Along the direction of fluid flow,the ideal displacement profile consisted of CO_(2) enriched bank,CO_(2) and CH_(4) mixed bank,CH_(4) enriched bank,and water enriched bank,whereas a remarkable gap in the displacement profiles of the dominant and non-dominant seepage directions was observed.4)The potential of CH_(4) output might vary greatly among different wellbores.The producers along the dominant seepage direction held more potential for CH_(4) recovery in the short-term,while those along the non-dominant seepage direction avoided becoming invalid only if a long-time injection measure was taken for the injectors.These findings pave the way to understand fluid seepage in real complex reservoirs during CO_(2)-ECBM and conduct further field projects.
基金This work was financially supported by the University Synergy Innovation Program of Anhui Province(No.GXXT-2021-018)the Natural Science Research Project of Anhui University(Nos.KJ2020A0315,KJ2020A0317)+2 种基金the Natural Science Foundation of Anhui Province(No.2108085MD134)the National Natural Science Foundation of China(No.41902168)the Foundation of State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing(No.PRP/open-2005).
文摘Three-dimensional(3D)reconstruction of the equivalent pore network model(PNM)using X-ray computed tomography(CT)data are of significance for studying the CO_(2)-enhanced coalbed methane recovery(CO_(2)-ECBM).The docking among X-ray CT technology,MATLAB,with COMSOL software not only can realize the 3D reconstruction of PNM,but also the CO_(2)-ECBM process simulation.The results show that the Median filtering algorithm enabled the de-noising of the original 2D CT slices,the image segmentation of all slices was realized based on the selected threshold,and the PNM can be constructed based on the Maximum Sphere algorithm.The mathematical model of CO_(2)-ECBM process fully coupled the expanded Langmuir equation.At the same time for CO_(2)injection,CH_(4)pressure tends to decrease with the increase of CO_(2)pressure,but its difference is not obvious.The CH_(4)pressure in the slice center changed a lot,while at the edge it changed a little under different CO_(2)pressures.The injected CO_(2)was transported to matrix along the macro and micro-fractures with continuous flow.The injected CO_(2)first replaced the adsorbed CH_(4)by covering the inner surface of macro-pores and meso-pores to form the single molecular layer adsorption of CO_(2).Then they migrated to micro-pores by Fick’s diffusion,sliding flow,and surface diffusion.Furthermore,the CO_(2)replaced CH_(4)adsorbed by volumetric filling in micro-pores,and formed the multi-molecular layer adsorption of CO_(2).The gas pressure and migration path between CO_(2)and CH_(4)are opposite.This study can provide a theoretical basis for studying digital rock physics technology and enrich the development of CO_(2)-ECBM technology.
