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
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
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.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.
