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Factors influencing methane diffusion behaviors in micro-nano coal pores: a comprehensive study

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Frontiers of Earth Science 2023年第1期17卷 71-86页

作者： Xianglong FANG Dameng LIU Yingfang ZHOU Xiaobo LIU Yidong CAI School of Energy Resources China University of GeosciencesBeijing 100083China Coal reservoir Laboratory of National Engineering Research Center of CBM Development&Utilization China University of GeosciencesBeijing 100083China School of Engineering Fraser Noble BuildingKing's CollegeUniversity of AberdeenAB243UE AberdeenUK Postdoctoral Workstation of Applied Technology Research Institute Northeast Petroleum UniversityDaqing 163318China

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.

关键词： coalbed methane reservoir micro-characteristic diffusion coefficient grey relational analysis

Geochemical Characters of Water Coproduced with coalbed Gas and Shallow Groundwater in Liulin Coalfield of China

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Acta Geologica Sinica(English Edition) 2013年第6期87卷 1690-1700页

作者： YANG Mei JU Yiwen LIU Guijian TONG Li KANG Yu HOU Quanlin College of Resources and Environment University of Chinese Academy Sciences Key Lab of Computational Geodynamics of Chinese Academy of Sciences College of Earth Science University of Chinese Academy Sciences School of Earth and Space Sciences University of Science and Technology of China Research Center for Process Pollution Control National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology Institute of Process EngineeringChinese Academy of Sciences University of Chinese Academy Sciences

To reveal the geochemical characters of water coproduced with coalbed gas and shallow groundwater,water samples were collected from 12 wells of coalbed methane and 7 wells of shallow groundwater.The pH,CODMn,fCO2,total dissolved solids （TDS）,total hardness,and concentrations of metasilicic acid,sodium and kalium,calcium ion,magnesium ion,ammonium iron,bicarbonate ion,carbonate,chloride,sulfate ion,nitrate ion,fluoride,lithium,zinc,nickel,manganese,iron,boron,barium,etc.of the samples were measured.Research results showed the following：（1） Concentrations of TDS,chloride,fluoride,sodium and kalium,ammonium,iron,and barium in the water coproduced with coalbed gas exceeded the national standards of China; however,physical,chemical,and biological properties of shallow groundwater could meet the national standard.（2） The water produced from coalbed contained mainly Na-Cl·HCO3,with average TDS of 4588.5 ppm,whereas shallow groundwater contained a mixture of chemicals including Na.Mg.Ca-HCO3·SO4 and Na.Mg-HCO3·SO4,with average TDS of 663.8 ppm.（3） In general,it was observed that bicarbonate and sodium accumulated in a reducing environment and deeper system,while depletion of hydrogen ions and dissolution of sulfate,calcium,and magnesium occurred in a redox environment and shallow system.（4） Sodium and kalium,ammonium,chloride,and bicarbonate ions were the main ions found in the study area.

关键词： coalbed methane reservoir geochemical evolution main ions produced water shallow groundwater

Dynamic-Change Laws of the Porosity and Permeability of Low-to Medium-Rank Coals under Heating and Pressurization Treatments in the Eastern Junggar Basin,China

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Journal of Earth Science 2018年第3期29卷 607-615页

作者： Gang Wang Yong Qin Jian Shen Shuyuan Chen Beibei Han Xiaoting Zhou Key Laboratory of coalbed methane Resources and reservoir Formation Process of the Ministry of Education China University of Mining and TechnologyXuzhou 221116China Key Laboratory of Resource Survey and Research of Hebei Province Hebei University of EngineeringHandan 056038China China Chemical Geology and Mine Bureau Beijing 100013China Institute of Technology East China Jiaotong UniversityNanchang 330100China

Deep coalbed methane exists in high-temperature and high-pressure reservoirs. To elucidate the dynamic-change laws of the deep coal reservoir porosity and permeability characteristics in the process of coalbed methane production, based on three pieces of low- to medium-rank coal samples in the eastern Junggar Basin, Xinjiang, we analyse their mercury-injection pore structures. We measured the porosity and permeability of the coal samples at various temperatures and confining pressures by high-temperature and confining pressure testing. The results show that the porosity of a coal sample decreases exponentially with increasing effective stress. With increasing temperature, the initial porosity increases for two pieces of relatively low-rank coal samples. The increased rate of porosity decreases with increasing confining pressure. With increasing temperature, the initial porosity of a relatively high-rank coal sample decreases, and the rate of change of the porosity become faster. An exponential relationship exists between the porosity and permeability. With increasing coal rank, the initial porosity and permeability decrease. The change rate of the permeability decreases with increasing porosity.

关键词： high-temperature and confining pressure coalbed methane reservoir porosity permeability dynamic change.

Mechanism of pore pressure variation in multiple coal reservoirs,western Guizhou region,South China

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Frontiers of Earth Science 2021年第4期15卷 770-789页

作者： Wei JU Zhaobiao YANG Yulin SHEN Hui YANG Geoff WANG Xiaoli ZHANG Shengyu WANG Key Laboratory of coalbed methane Resources and reservoir Formation Process(Ministry of Education) China University of Mining and TechnologyXuzhou 221008China School of Resources and Geosciences China University of Mining and TechnologyXuzhou 221116China School of Chemical Engineering The University of QueenslandBrisbane St Lucia 4072Australia

Pore pressure is an important parameter in coalbed methane(CBM)exploration and development;however,the distribution pattern and mechanism for pore pressure differences in the Upper Permian CBM reservoirs are poorly understood in the western Guizhou region of South China.In this study,lateral and vertical variations and mechanisms for pore pressure differences are analyzed based on 126 injection-falloff and in-situ stress well test data measured in Permian coal reservoirs.Generally,based on the pore pressure gradient and coefficient in coal reservoirs of the western Guizhou region,five zones can be delineated laterally:the mining areas of Zhina,northem Liupanshui,northern Guizhou,northwestern Guizhou and southern Liupanshui.Vertically,there are two main typical patterns:i)the pore pressure gradient(or coefficient)is nearly unchanged in different coal reservoirs,and ii)the pore pressure gradient(or coefficient)has cyclic variations in a borehole profile with multiple coal seams,which suggests the existence of a"superimposed CBM system".The mechanism analysis indicates that coal permeability,thermal evolution stage and hydrocarbon generation contribute little to pore pressure differences in coal reservoirs in the western Guizhou region.The present-day in-situ stress field,basement structure and tectonic activity may be the dominant factors affecting lateral pore pressure differences.The sealing capacity of caprocks and the present-day in-situ stress field are significant para-meters causing vertical pore pressure differences in coal reservoirs.These results are expected to provide new geological references for CBM exploration and develop-ment in the western Guizhou region.

关键词： pore pressure difference influencing factor coalbed methane reservoir Upper Permian western Guizhou region

Experimental investigation of propagation mechanisms and fracture morphology for coalbed methane reservoirs

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Petroleum Science 2018年第4期15卷 815-829页

作者： Chi Ai Xiao-Xuan Li Jun Zhang Dan Jia Wen-Jing Tan College of Petroleum Engineering Northeast Petroleum University College of Geoscience and Technology China University of Petroleum (East China)

Fracture propagation mechanisms in coalbed methane(CBM) reservoirs are very complex due to the development of the internal cleat system. In this paper, the characteristics of initiation and propagation of hydraulic fractures in coal specimens at different angles between the face cleat and the maximum horizontal principal stress were investigated with hydraulic fracturing tests. The results indicate that the interactions between the hydraulic fractures and the cleat system have a major effect on fracture networks. "Step-like’’ fractures were formed in most experiments due to the existence of discontinuous butt cleats. The hydraulic fractures were more likely to divert or propagate along the butt cleat with an increase in the angles and a decrease in the horizontal principal stress difference. An increase in the injection rate and a decrease in the fracturing fluid viscosity were more conducive to fracture networks. In addition, the influence on fracture propagation of the residual coal fines in the wellbore was also studied. The existence of coal fines was an obstacle in fracturing, and no effective connection can be formed between fractures. The experimental investigation revealed the fracture propagation mechanisms and can provide guidance for hydraulic fracturing design of CBM reservoirs.

关键词： coalbed methane reservoir Butt cleat Propagation mechanisms Fracture morphology Step-like fractures

Pool-Forming Stages and Enrichment Models of Medium- to High-Rank coalbed methane

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Acta Geologica Sinica(English Edition) 2010年第6期84卷 1539-1546页

作者： SONG Yan ZHAO Mengjun HONG Feng LIU Shaobo QIN Shengfei WANG Hongyan Petroleum Geology Research and Laboratory Center Research Institute of Petroleum Exploration and Development CNPC Beijing 100083 China Yangtze University Jingzhou Hubei 434023 China Langfang Branch of Research Institute of Petroleum Exploration and Development CNPC Langfang Hebei 065007 China

The pool-forming mechanism of coalbed methane has its own characteristics.In this paper, based on studies on the typical coal-bearing basins in China,it is pointed out that the reservoir formation of medium- to high-rank coalbed methane has experienced three critical stages：the coalbed methane generation and adsorption stage,the coalbed adsorption capacity enhancement stage,and the coalbed methane desorption-diffusion and preservation stage.The regional tectonic evolution, hydrodynamic conditions and sealing conditions play important roles in the stage of coalbed methane desorption-diffusion and preservation.Medium- to high-rank coalbed methane has three types of enrichment models,that is,the most favorable,the relatively favorable,and the unfavorable enrichment models.

关键词： coalbed methane reservoir mechanism structure hydrodynamic model

Characteristics of in-situ stress and its controls on coalbed methane development in the southeastern Qinshui Basin,North China

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能源地球科学(英文)

能源地球科学(英文) 2020年第1期1卷 69-80页

作者： Lutong Cao Yanbin Yao Chao Cui Qinping Sun School of Energy Resource China University of GeosciencesBeijing100083China Coal reservoir Laboratory of the National Engineering Research Center of CBM Development&Utilization China University of GeosciencesBeijing100083China Research Institute of Petroleum Exploration and Development LangfangHebei065007China

In-situ stress is a key reservoir parameter to evaluate reservoir permeability,hydraulic fractures,coal seam deformation and coalbed methane(CBM)recovery.With limited CBM test wells in the Zhengzhuang field,southeast of the Qinshui basin,North China,the in-situ stress data is inadequate for CBM exploration and development.It is necessary to find a method to predicate in-situ stress through other exploration data such as geophysical well loggings.In this study,we provide a new well-logging databased model to predicate the in-situ stress based on 17 sets of well test data and comprehensive logging data.As a distinguished characteristic of this model,different structural compartmentalization of CBM reservoirs was considered.A regional adaptive residual strain index was introduced to the model.Based on the model,the in-situ stress distribution in the Zhengzhuang field were evaluated systematically,and the influences of in-situ stress on permeability and the propagation of hydro-fractures were discussed.Results indicate that the magnitude of the maximum(S_(Hmax),14.19e45.40 MPa)and minimum horizontal stresses(Shmin,10.62e28.38 MPa)and the gravitational stress(Sv,9.58e30.82 MPa)all show positive correlations with burial depths.The in-situ stress fields in the study area are characterized by 1)SHmax>Sv>Shmin in shallow layers(S_(hmin)and S_(Hmax)>Sv>S_(hmin)in the depth of 700e1050 m,suggesting a transformed regime;and 3)S_(Hmax)>Sv>S_(hmin)in deep layers(>1050 m),indicating a strike-slip faulting stress regime.The S_(Hmax)in the study area is orientated by NE-SW,with a trend of 40e49.Resulted from the change of the in-situ stress regimes from shallow(500 m)to deep layers(~1000 m),the reservoir permeability variation shows a typical increase followed by decrease.The presence of natural fractures significantly affect the propagation pattern of hydraulic fractures,and the length difference between the major and branch fractures increases wi

关键词： In situ stress coalbed methane reservoir Permeability Hydraulic fracture

A Comprehensive Model for Evaluating coalbed methane reservoirs in China

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Acta Geologica Sinica(English Edition) 2008年第6期82卷 1253-1270页

作者： YAO Yanbin LIU Dameng TANG Dazhen HUANG Wenhui TANG Shuheng CHE Yao School of Energy Resources China University of Geosciences Beijing 100083 China

coalbed methane reservoir （CBMR） evaluation is important for choosing the prospective target area for coalbed methane exploration and production. This study aims at identifying the characteristic parameters and methods to evaluate CBMR. Based on the geological surveys, laboratory measurements and field works, a four-level analytic hierarchy process （AHP） model for CBMR evaluation is proposed. In this model, different weights are prioritized and assigned on the basis of three main criteria （including reservoir physical property, storage capacity and geological characteristics）, 15 sub-criteria, and 18 technical alternatives; the later of which are discussed in detail. The model was applied to evaluate the CBMR of the Permo-Carboniferous coals in the Qinshui Basin, North China. This GIS-based fuzzy AHP comprehensive model can be used for the evaluation of CBMR of medium-high rank （mean maximum vitrinite reflectance 〉0.5 %） coal districts in China.

关键词： coalbed methane reservoir reservoir evaluation reservoir characterization comprehensive model Fuzzy Hierarchy Process Approach （FAHP）

The Classification and Model of coalbed methane reservoirs

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Acta Geologica Sinica(English Edition) 2004年第3期78卷 662-666页

作者： SUXianbo LINXiaoying SONGYan ZHAOMengjun HenanUniversityoftheSciences JiaozuoHenan454000 ResearchInstituteofPetroleumExplorationandDevelopment PetroChinaBeijing100083

coalbed methane has been explored in many basins worldwide for 30 years, and has been developed commercially in some of the basins. Many researchers have described the characteristics of coalbed methane geology and technology systematically. According to these investigations, a coalbed methane reservoir can be defined: 'a coal seam that contains some coalbed methane and is isolated from other fluid units is called a coalbed methane reservoir'. On the basis of anatomization, analysis, and comparison of the typical coalbed methane reservoirs, coalbed methane reservoirs can be divided into two classes: the hydrodynamic sealing coalbed methane reservoirs and the self-sealing coalbed methane reservoirs. The former can be further divided into two sub-classes: the hydrodynamic capping coalbed methane reservoirs, which can be divided into five types and the hydrodynamic driving coalbed methane reservoirs, which can be divided into three types. The latter can be divided into three types. Currently, hydrodynamic sealing reservoirs are the main target for coalbed methane exploration and development; self-sealing reservoirs are unsuitable for coalbed methane exploration and development, but they are closely related with coal mine gas hazards. Finally, a model for hydrodynamic sealing coalbed methane reservoirs is established.

关键词： coalbed methane reservoir classification reservoir model hydrodynamics reservoir boundary