Many mature onshore oilfields have entered a high-water-cut stage,with reservoir recovery approaching economic limits.Converting these depleted or nearly depleted reservoirs into underground gas storage(UGS)facilities...Many mature onshore oilfields have entered a high-water-cut stage,with reservoir recovery approaching economic limits.Converting these depleted or nearly depleted reservoirs into underground gas storage(UGS)facilities offers an efficient way to leverage their substantial storage potential.During cyclic gas injection and withdrawal,however,the reservoir experiences complex three-phase flow and repeated stress fluctuations,which can induce rock fatigue,inelastic deformation,and ultimately sand production.This study uses controlled physical experiments to simulate sand production in reservoir rocks subjected to alternating gas injection and production under three-phase conditions.After preparing oil-water-saturated cores through waterflooding,gas is introduced to perform repeated displacement cycles.Polynomial models relating core mass loss to water-oil ratio and cycle number are developed using the Newton interpolation method,enabling prediction of sand production under various operating conditions.Results show that,within the critical pressure-difference range for sand onset,permeability increases with water-oil ratio.When the water-oil ratio lies between 0.3 and 1,sand production decreases progressively;beyond a ratio of 1,sand production increases with further increases in water-oil ratio.The number of displacement cycles exerts a dominant influence:sand production remains relatively stable between 25 and 55 cycles but rises sharply thereafter.Average sand production during cycles 55–100 is 5.27 times higher than during cycles 5–55.These findings indicate that cumulative structural damage to the rock framework intensifies significantly with repeated cycling,making cycle number a critical factor governing sand production in UGS operations.展开更多
Wettability affects the immiscible flow process of the gas-water phases in coalbed methane reservoirs,which has an important effect on coalbed methane production.The sessile drop method,infrared spectroscopy and atomi...Wettability affects the immiscible flow process of the gas-water phases in coalbed methane reservoirs,which has an important effect on coalbed methane production.The sessile drop method,infrared spectroscopy and atomic force microscopy(AFM)were used to study the wettability,functional groups and pore structure of 8 coal rocks with middle ranks from the Qinshui Basin,North China,and the Junggar Basin,Northwest China.The pore structure of the coal sample,including the porosity,number of pores,pore area,pore diameter,percentage of different types of pores and roughness under the scale of 50 mm,was determined using the Nanoscope and Gwyddion analysis methods.The relationships between the pore structure,functional groups,coal surface roughness and wettability were studied.The results show that the larger the proportion of macropores on the coal surface is,the stronger the hydrophilicity of coal.The more oxygen-containing functional groups there are,the better the wettability of coal and rock.The contact angle has a sinusoidal relationship with the roughness due to the change in the adsorption point.For coal with very low or very high roughness,the contact angle is negatively correlated with the roughness,while for coal with low to average roughness,the contact angle is significantly positively correlated with the roughness.This work provides new insights into the interactions between water molecules and the coal pore surface.展开更多
The utilization of hydraulic fracturing for the extraction of natural gas hydrates in maritime environments has been relatively underexplored in the existing literature.This study introduces a novel approach by employ...The utilization of hydraulic fracturing for the extraction of natural gas hydrates in maritime environments has been relatively underexplored in the existing literature.This study introduces a novel approach by employing a fully implicit integration method to construct a two-dimensional temperature distribution model of the wellbore.The model considers critical parameters such as fracturing fluid time,initial temperature,and fracturing fluid displacement to forecast the temperature data of the wellbore and its surrounding environments throughout the entire fracturing process.The investigation reveals that the initial temperature of the fracturing liquid and the duration of the fracturing process exert a substantial influence on the wellbore temperature,whereas the impact of fracturing fluid displacement is found to be minimal.Furthermore,a comparative analysis between the results derived from the proposed model and those obtained from traditional steady-state formulas substantiates the accuracy and efficacy of the developed model.This study significantly advances our comprehension of temperature dynamics within wellbores during hydraulic fracturing operations in maritime environments,thereby offering valuable insights for future endeavors in natural gas hydrate extraction.展开更多
During the development of high-sulfur gas reservoirs, the precipitation and deposition of elemental sulfur can lead to a reduction in reservoir porosity and permeability. Previous studies focus on the well production ...During the development of high-sulfur gas reservoirs, the precipitation and deposition of elemental sulfur can lead to a reduction in reservoir porosity and permeability. Previous studies focus on the well production with optimized operational parameters, but the effect of sulfur deposition is not included,which impacts fracturing parameters, well production, and economic evaluation. Therefore, this work proposes a reasonable approach for parameter optimization considering sulfur. The variation of porosity and permeability are first evaluated during sulfur deposition. After that, fracture half-length, fracture spacing, fracture conductivity, and fracture distribution are optimized with orthogonalization factor analysis, and the influence of sulfur deposition on different fracture parameters are detailed analyzed.The results shown that the fracture half-length and fracture conductivity are greatly affected by sulfur deposition. Finally, net profit value is applied to obtain the optimal fracture spacing interval. With economic evaluation, the optimal fracture spacing interval of 125 m-150 m is determined considering the net profit and the payback period. This work provides a useful economic method for fracture parameter optimization high-sulfur gas reservoirs, which benefits for the development and production of gas reservoirs.展开更多
Petrophysics of coals directly affects the development of coalbed methane(CBM).Based on the analysis of the representative academic works at home and abroad,the recent progress on petrophysics characteristics was revi...Petrophysics of coals directly affects the development of coalbed methane(CBM).Based on the analysis of the representative academic works at home and abroad,the recent progress on petrophysics characteristics was reviewed from the aspects of the scale-span porefracture structure,permeability,reservoir heterogeneity,and its controlling factors.The results showed that the characterization of pore-fracture has gone through three stages:qualitative and semiquantitative evaluation of porefracture by various techniques,quantitatively refined characterization of pore-fracture by integrating multiple methods including nuclear magnetic resonance analysis,liquid nitrogen,and mercury intrusion,and advanced quantitative characterization methods of pore-fracture by high-precision experimental instruments(focused-ion beam-scanning electron microscopy,small-angle neutron scattering and computed tomography scanner)and testing methods(m-CT scanning and X-ray diffraction).The effects of acoustic field can promote the diffusion of CBM and generally increase the permeability of coal reservoirs by more than 10%.For the controlling factors of reservoir petrophysics,tectonic stress is the most crucial factor in determining permeability,while the heterogeneity of CBM reservoirs increases with the enhancement of the tectonic deformation and stress field.The study on lithology heterogeneity of deep and high-dip coal measures,the spatial storage-seepage characteristics with deep CBM reservoirs,and the optimizing production between coal measures should be the leading research directions.展开更多
The acoustic response of gas and/or water saturated coal rock is fundamental for establishing the correspondence between the physical properties of the coal reservoir and the characteristics of the well-logging respon...The acoustic response of gas and/or water saturated coal rock is fundamental for establishing the correspondence between the physical properties of the coal reservoir and the characteristics of the well-logging response,which is the technology essential for the geophysical exploration of coalbed methane(CBM).This acoustic response depends on water(Sw)and gas(Sg)saturation among other factors.In this study,we performed acoustic tests on dry and different gas-water saturated coal samples with different degrees of metamorphism and deformation,collected from several coal mining areas in China.These tests enabled us to analyze the influence of coal type and gas-water saturation on the acoustic response of CBM formations.Our results show that the acoustic velocity of P-wave and S-wave(Vp and Vs,respectively),and the relative anisotropy of and Vs,increased with increasing vitrinite reflectance,density,Vp and Sw.WithSw increasing from 0 to 100%,the growth rate of the acoustic velocity decreased with increasing vitrinite reflectance.The Vp/Vs ratio of tectonic coal was generally higher than that of primary coal.The growth rate of the relative anisotropy in tectonic coal was markedly higher than that in primary coal.展开更多
Recently, deeply-buried shale (depth > 3500 m) has become an attractive target for shale gas exploration and development in China. Gas-in-place (GIP) is critical to shale gas evaluation, but the GIP content of deep...Recently, deeply-buried shale (depth > 3500 m) has become an attractive target for shale gas exploration and development in China. Gas-in-place (GIP) is critical to shale gas evaluation, but the GIP content of deep shale and its controlling factors have rarely been investigated. To clarify this issue, an integrated investigation of deep gas shale (3740–3820 m depth) of the Lower Paleozoic Wufeng–Longmaxi Formations (WF–LMX) in the Dingshan area, Sichuan Basin had been carried out. Our results show that the GIP content of the studied WF–LMX shale in the Dingshan area ranges from 0.85 to 12.7 m^(3)/t, with an average of 3.5 m^(3)/t. Various types of pores, including organic matter (OM) pore and inorganic pore, are widely developed in the deep shale, with total porosity of 2.2 to 7.3% (average = 4.5%). The OM pore and clay-hosted pore are the dominant pore types of siliceous shale and clay-rich shale, respectively. Authigenic quartz plays a critical role in the protection of organic pores in organic-rich shales from compaction. The TOC content controls the porosity of shale samples, which is the major factor controlling the GIP content of the deep shale. Clay minerals generally play a negative role in the GIP content. In the Sichuan Basin, the deep and ultra-deep WF–LMX shales display the relatively high porosity and GIP contents probably due to the widespread of organic pores and better preservation, revealing great potentials of deep and ultra-deep shale gas. From the perspective of rock mechanical properties, deep shale is the favorable exploration target in the Sichuan Basin at present. However, ultra-deep shale is also a potential exploration target although there remain great challenges.展开更多
Stress sensitivity has significant negative effects on the permeability and production of coalbed methane(CBM)reservoirs.To effectively minimize these negative effects,the degree of stress sensitivity during the CBM p...Stress sensitivity has significant negative effects on the permeability and production of coalbed methane(CBM)reservoirs.To effectively minimize these negative effects,the degree of stress sensitivity during the CBM production process should be carefully studied.In this work,the curvature of the stress-sensitivity curve was adopted to explore the degree of stress sensitivity,dividing the stress-sensitivity curve and the drainage process into five stress stages:sharp decrease,rapid decrease,low-speed decrease,slower decrease and harmless with four critical stress points—transition,sensitivity,relief and harmless.The actual stages were determined by the initial permeability,stress-sensitivity coefficient and difference between the reservoir pressure and desorption pressure.The four critical stress points did not completely exist in the stress-sensitivity curve.With an increase in the initial permeability of coal,the number of existing critical stresses increases,leading to different gas-water drainage strategies for CBM wells.For reservoirs with a certain stress-sensitivity coefficient,the permeability at the sensitive stress point was successively greater than that at the transition,relief and the harmless stresses.When the stress-sensitivity coefficient is different,the stage is different at the beginning of drainage,and with an increase in the stress-sensitivity coefficient,the decrease rate of the permeability increases.Therefore,the stress-sensitivity coefficient determines the ability to maintain stable CBM production.For well-fractured CBM reservoirs,with a high stress-sensitivity coefficient,permeability damage mainly occurs when the reservoir pressure is less than the relief stress;therefore,the depressurization rate should be slow.For CBM reservoirs with fewer natural fractures,the reverse applies,and the depressurization rate can be much faster.The higher the difference between the reservoir and desorption pressures,the higher the effective stress and permeability damage after desorption,resulting in a much longer drainage time and many difficulties for the desorption of coalbed methane.The findings of this study can help better understand and minimize the negative effects of stress sensitivity during the CBM production process.展开更多
Gas diffusion in the coal matrix plays a significant role in forecasting the production performance of coalbed methane(CBM)wells.To better understand methane diffusion behavior,a systematic study was performed on vari...Gas diffusion in the coal matrix plays a significant role in forecasting the production performance of coalbed methane(CBM)wells.To better understand methane diffusion behavior,a systematic study was performed on various rank coals with vitrinite reflectance(Ro,m)ranging from 0.46%to 2.79%.Multiple experiments,including coal petrographic analysis,field emission scanning electron microscopy(FESEM),low-temperature N2 adsorption/desorption,and mercury intrusion porosimetry(MIP),were conducted to quantitatively characterize the multiscale micro-nano pore system in different rank coals,which showed that the pore structure of coals exhibited a multimodal pore size and volume distribution.Isothermal adsorption-diffusion experiments using the volumetric method were also performed to understand the methane diffusion characteristics in the micro-nano pores of the coal reservoir.The applicability of the multiporous diffusion model is verified,and methane diffusion in the multi-scale pores of coal reservoirs exhibits the characteristics of early fast diffusion,transitional diffusion in the medium term,and slow diffusion in the later period.In addition,the factors affecting methane diffusion in coals were systematically analyzed,and gray relational analysis(GRA)was employed to analyze and identify the importance of these factors on methane diffusion.The results show the impact ranking of factors,in order from the most important to the least:particle size>moisture>surface area>pore volume>pressure>coal rank>temperature in all of three diffusion stages.These findings are helpful for forecasting production performance and enhancing the production efficiency of CBM.展开更多
Coal-related resources, as a popular development in recent years, is the focus of research in the field of coalbed methane (CBM), coal measure gases, coal-associated rare earth resources and nonmetallic minerals (Moor...Coal-related resources, as a popular development in recent years, is the focus of research in the field of coalbed methane (CBM), coal measure gases, coal-associated rare earth resources and nonmetallic minerals (Moore, 2012;Dai and Finkelman, 2018;Qin et al., 2018). Due to its complexity in concentration, occurrence and exploitation, many key issues need to be addressed (Sayed et al., 2017;Bera et al., 2022;Liu et al., 2022).展开更多
基金National Science and Technology Major Project(2025ZD1406805)“Key Technology for Efficient Construction of New Underground Gas Storage”Research Project of CNPC(2023DJ8308)“Research on Wellbore Treatment and Rapid Construction Method of Oil and Gas Reservoir and Thin Salt Layer Storage”National Key Research and Development Program of China(Grant No.2025ZD1406805 and Grant No.2025ZD1011105).
文摘Many mature onshore oilfields have entered a high-water-cut stage,with reservoir recovery approaching economic limits.Converting these depleted or nearly depleted reservoirs into underground gas storage(UGS)facilities offers an efficient way to leverage their substantial storage potential.During cyclic gas injection and withdrawal,however,the reservoir experiences complex three-phase flow and repeated stress fluctuations,which can induce rock fatigue,inelastic deformation,and ultimately sand production.This study uses controlled physical experiments to simulate sand production in reservoir rocks subjected to alternating gas injection and production under three-phase conditions.After preparing oil-water-saturated cores through waterflooding,gas is introduced to perform repeated displacement cycles.Polynomial models relating core mass loss to water-oil ratio and cycle number are developed using the Newton interpolation method,enabling prediction of sand production under various operating conditions.Results show that,within the critical pressure-difference range for sand onset,permeability increases with water-oil ratio.When the water-oil ratio lies between 0.3 and 1,sand production decreases progressively;beyond a ratio of 1,sand production increases with further increases in water-oil ratio.The number of displacement cycles exerts a dominant influence:sand production remains relatively stable between 25 and 55 cycles but rises sharply thereafter.Average sand production during cycles 55–100 is 5.27 times higher than during cycles 5–55.These findings indicate that cumulative structural damage to the rock framework intensifies significantly with repeated cycling,making cycle number a critical factor governing sand production in UGS operations.
基金funded by the National Natural Science Foundation of China(Grant Nos.41922016,42130806,41830427 and 41872179).
文摘Wettability affects the immiscible flow process of the gas-water phases in coalbed methane reservoirs,which has an important effect on coalbed methane production.The sessile drop method,infrared spectroscopy and atomic force microscopy(AFM)were used to study the wettability,functional groups and pore structure of 8 coal rocks with middle ranks from the Qinshui Basin,North China,and the Junggar Basin,Northwest China.The pore structure of the coal sample,including the porosity,number of pores,pore area,pore diameter,percentage of different types of pores and roughness under the scale of 50 mm,was determined using the Nanoscope and Gwyddion analysis methods.The relationships between the pore structure,functional groups,coal surface roughness and wettability were studied.The results show that the larger the proportion of macropores on the coal surface is,the stronger the hydrophilicity of coal.The more oxygen-containing functional groups there are,the better the wettability of coal and rock.The contact angle has a sinusoidal relationship with the roughness due to the change in the adsorption point.For coal with very low or very high roughness,the contact angle is negatively correlated with the roughness,while for coal with low to average roughness,the contact angle is significantly positively correlated with the roughness.This work provides new insights into the interactions between water molecules and the coal pore surface.
基金supported by National Natural Science Foundation of China(52074248)Fundamental Research Funds for the Central Universities(2652022207).
文摘The utilization of hydraulic fracturing for the extraction of natural gas hydrates in maritime environments has been relatively underexplored in the existing literature.This study introduces a novel approach by employing a fully implicit integration method to construct a two-dimensional temperature distribution model of the wellbore.The model considers critical parameters such as fracturing fluid time,initial temperature,and fracturing fluid displacement to forecast the temperature data of the wellbore and its surrounding environments throughout the entire fracturing process.The investigation reveals that the initial temperature of the fracturing liquid and the duration of the fracturing process exert a substantial influence on the wellbore temperature,whereas the impact of fracturing fluid displacement is found to be minimal.Furthermore,a comparative analysis between the results derived from the proposed model and those obtained from traditional steady-state formulas substantiates the accuracy and efficacy of the developed model.This study significantly advances our comprehension of temperature dynamics within wellbores during hydraulic fracturing operations in maritime environments,thereby offering valuable insights for future endeavors in natural gas hydrate extraction.
基金supported by the National Natural Science Foundation of China(52074248,52474052)the Fundamental Research Funds for the Central Universities(2652022207).
文摘During the development of high-sulfur gas reservoirs, the precipitation and deposition of elemental sulfur can lead to a reduction in reservoir porosity and permeability. Previous studies focus on the well production with optimized operational parameters, but the effect of sulfur deposition is not included,which impacts fracturing parameters, well production, and economic evaluation. Therefore, this work proposes a reasonable approach for parameter optimization considering sulfur. The variation of porosity and permeability are first evaluated during sulfur deposition. After that, fracture half-length, fracture spacing, fracture conductivity, and fracture distribution are optimized with orthogonalization factor analysis, and the influence of sulfur deposition on different fracture parameters are detailed analyzed.The results shown that the fracture half-length and fracture conductivity are greatly affected by sulfur deposition. Finally, net profit value is applied to obtain the optimal fracture spacing interval. With economic evaluation, the optimal fracture spacing interval of 125 m-150 m is determined considering the net profit and the payback period. This work provides a useful economic method for fracture parameter optimization high-sulfur gas reservoirs, which benefits for the development and production of gas reservoirs.
基金funded by the National Natural Science Foundation of China(Grant Nos.41830427,41772160 and 41922016)。
文摘Petrophysics of coals directly affects the development of coalbed methane(CBM).Based on the analysis of the representative academic works at home and abroad,the recent progress on petrophysics characteristics was reviewed from the aspects of the scale-span porefracture structure,permeability,reservoir heterogeneity,and its controlling factors.The results showed that the characterization of pore-fracture has gone through three stages:qualitative and semiquantitative evaluation of porefracture by various techniques,quantitatively refined characterization of pore-fracture by integrating multiple methods including nuclear magnetic resonance analysis,liquid nitrogen,and mercury intrusion,and advanced quantitative characterization methods of pore-fracture by high-precision experimental instruments(focused-ion beam-scanning electron microscopy,small-angle neutron scattering and computed tomography scanner)and testing methods(m-CT scanning and X-ray diffraction).The effects of acoustic field can promote the diffusion of CBM and generally increase the permeability of coal reservoirs by more than 10%.For the controlling factors of reservoir petrophysics,tectonic stress is the most crucial factor in determining permeability,while the heterogeneity of CBM reservoirs increases with the enhancement of the tectonic deformation and stress field.The study on lithology heterogeneity of deep and high-dip coal measures,the spatial storage-seepage characteristics with deep CBM reservoirs,and the optimizing production between coal measures should be the leading research directions.
基金This research was funded by the National Natural Science Foundation of China(Grant Nos.42130806,41922016,41830427 and 41772160).
文摘The acoustic response of gas and/or water saturated coal rock is fundamental for establishing the correspondence between the physical properties of the coal reservoir and the characteristics of the well-logging response,which is the technology essential for the geophysical exploration of coalbed methane(CBM).This acoustic response depends on water(Sw)and gas(Sg)saturation among other factors.In this study,we performed acoustic tests on dry and different gas-water saturated coal samples with different degrees of metamorphism and deformation,collected from several coal mining areas in China.These tests enabled us to analyze the influence of coal type and gas-water saturation on the acoustic response of CBM formations.Our results show that the acoustic velocity of P-wave and S-wave(Vp and Vs,respectively),and the relative anisotropy of and Vs,increased with increasing vitrinite reflectance,density,Vp and Sw.WithSw increasing from 0 to 100%,the growth rate of the acoustic velocity decreased with increasing vitrinite reflectance.The Vp/Vs ratio of tectonic coal was generally higher than that of primary coal.The growth rate of the relative anisotropy in tectonic coal was markedly higher than that in primary coal.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.U19B6003-03-01 and 42030804)the Fundamental Research Funds for the Central Universities(No.2652019101).
文摘Recently, deeply-buried shale (depth > 3500 m) has become an attractive target for shale gas exploration and development in China. Gas-in-place (GIP) is critical to shale gas evaluation, but the GIP content of deep shale and its controlling factors have rarely been investigated. To clarify this issue, an integrated investigation of deep gas shale (3740–3820 m depth) of the Lower Paleozoic Wufeng–Longmaxi Formations (WF–LMX) in the Dingshan area, Sichuan Basin had been carried out. Our results show that the GIP content of the studied WF–LMX shale in the Dingshan area ranges from 0.85 to 12.7 m^(3)/t, with an average of 3.5 m^(3)/t. Various types of pores, including organic matter (OM) pore and inorganic pore, are widely developed in the deep shale, with total porosity of 2.2 to 7.3% (average = 4.5%). The OM pore and clay-hosted pore are the dominant pore types of siliceous shale and clay-rich shale, respectively. Authigenic quartz plays a critical role in the protection of organic pores in organic-rich shales from compaction. The TOC content controls the porosity of shale samples, which is the major factor controlling the GIP content of the deep shale. Clay minerals generally play a negative role in the GIP content. In the Sichuan Basin, the deep and ultra-deep WF–LMX shales display the relatively high porosity and GIP contents probably due to the widespread of organic pores and better preservation, revealing great potentials of deep and ultra-deep shale gas. From the perspective of rock mechanical properties, deep shale is the favorable exploration target in the Sichuan Basin at present. However, ultra-deep shale is also a potential exploration target although there remain great challenges.
基金This research was supported by National Science and Technology Major Project(No.2017ZX05064)the National Natural Science Foundation of China(Grant Nos.42130806,41830427,and 41922016).
文摘Stress sensitivity has significant negative effects on the permeability and production of coalbed methane(CBM)reservoirs.To effectively minimize these negative effects,the degree of stress sensitivity during the CBM production process should be carefully studied.In this work,the curvature of the stress-sensitivity curve was adopted to explore the degree of stress sensitivity,dividing the stress-sensitivity curve and the drainage process into five stress stages:sharp decrease,rapid decrease,low-speed decrease,slower decrease and harmless with four critical stress points—transition,sensitivity,relief and harmless.The actual stages were determined by the initial permeability,stress-sensitivity coefficient and difference between the reservoir pressure and desorption pressure.The four critical stress points did not completely exist in the stress-sensitivity curve.With an increase in the initial permeability of coal,the number of existing critical stresses increases,leading to different gas-water drainage strategies for CBM wells.For reservoirs with a certain stress-sensitivity coefficient,the permeability at the sensitive stress point was successively greater than that at the transition,relief and the harmless stresses.When the stress-sensitivity coefficient is different,the stage is different at the beginning of drainage,and with an increase in the stress-sensitivity coefficient,the decrease rate of the permeability increases.Therefore,the stress-sensitivity coefficient determines the ability to maintain stable CBM production.For well-fractured CBM reservoirs,with a high stress-sensitivity coefficient,permeability damage mainly occurs when the reservoir pressure is less than the relief stress;therefore,the depressurization rate should be slow.For CBM reservoirs with fewer natural fractures,the reverse applies,and the depressurization rate can be much faster.The higher the difference between the reservoir and desorption pressures,the higher the effective stress and permeability damage after desorption,resulting in a much longer drainage time and many difficulties for the desorption of coalbed methane.The findings of this study can help better understand and minimize the negative effects of stress sensitivity during the CBM production process.
基金This research was funded by the National Natural Science Foundation of China(Grant Nos.41922016,41830427,and 41772160)the Fundamental Research Funds for the Central Universities(No.2652019264).
文摘Gas diffusion in the coal matrix plays a significant role in forecasting the production performance of coalbed methane(CBM)wells.To better understand methane diffusion behavior,a systematic study was performed on various rank coals with vitrinite reflectance(Ro,m)ranging from 0.46%to 2.79%.Multiple experiments,including coal petrographic analysis,field emission scanning electron microscopy(FESEM),low-temperature N2 adsorption/desorption,and mercury intrusion porosimetry(MIP),were conducted to quantitatively characterize the multiscale micro-nano pore system in different rank coals,which showed that the pore structure of coals exhibited a multimodal pore size and volume distribution.Isothermal adsorption-diffusion experiments using the volumetric method were also performed to understand the methane diffusion characteristics in the micro-nano pores of the coal reservoir.The applicability of the multiporous diffusion model is verified,and methane diffusion in the multi-scale pores of coal reservoirs exhibits the characteristics of early fast diffusion,transitional diffusion in the medium term,and slow diffusion in the later period.In addition,the factors affecting methane diffusion in coals were systematically analyzed,and gray relational analysis(GRA)was employed to analyze and identify the importance of these factors on methane diffusion.The results show the impact ranking of factors,in order from the most important to the least:particle size>moisture>surface area>pore volume>pressure>coal rank>temperature in all of three diffusion stages.These findings are helpful for forecasting production performance and enhancing the production efficiency of CBM.
文摘Coal-related resources, as a popular development in recent years, is the focus of research in the field of coalbed methane (CBM), coal measure gases, coal-associated rare earth resources and nonmetallic minerals (Moore, 2012;Dai and Finkelman, 2018;Qin et al., 2018). Due to its complexity in concentration, occurrence and exploitation, many key issues need to be addressed (Sayed et al., 2017;Bera et al., 2022;Liu et al., 2022).
