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coalbed methane genesis, occurrence and accumulation in China

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Petroleum Science 2012年第3期9卷 269-280页

作者： Song Yan Liu Shaobo Zhang Qun Tao Mingxin Zhao Mengjun Hong Feng Research Institute of Petroleum Exploration&Development Beijing 100083China China University of Petroleum Beijing 102249China Xi'an Research Institute of China Coal Technology&Engineering Group Corp. Shaanxi 710077China Beijing Normal University Beijing 100875China

coalbed methane （CBM） is an important type of unconventional gas. Commercial development of CBM in America has been very successful since the 1980s. The CBM industry in Australia and Canada has developed rapidly during the last decade. Commercial development of CBM in China started in the 1990s, and has made great progress. The geological theory of CBM in China has achieved great advancement in genesis, occurrence and accumulation. On the aspect of CBM genesis, five CBM genetic types （primary biogenic gas, secondary biogenic gas, thermal degradation gas, pyrolysis gas and mixed gas） are identified by studying the geochemical characteristics of CBM, and a tracing indicator system is established. The discovery of secondary biogenic gas in medium-high rank coal reservoirs has widened the potential of CBM resources. On the aspect of CBM occurrence, the gas adsorption regulation under combined action of temperature and pressure is revealed by conducting adsorption experiments of different coal ranks under varying temperature and pressure conditions. Besides, by applying the adsorption potential theory in CBM research, the adsorption model under combined action of temperature and pressure is established. The new model can predict CBM resources accurately, and overcome the limitation of the traditional Langmuir model which uses just a single factor to describe the adsorption characteristics of deep buried coal. On the aspect of CBM accumulation, it is proposed that there are three evolutionary stages during CBM accumulation, including gas generation and adsorption, unsaturated gas adsorption, gas desorption-diffusion and preservation. Controlled by tectonic evolution, hydrodynamics and sealing conditions, CBM tends to be regionally enriched in synclines. Advances in geological theory of CBM in China can not only improve understanding of natural gas, but also provide new ideas for further exploration of CBM.

关键词： China coalbed methane genetic type secondary biogenic gas adsorption model syncline enrichment

Sorption of methane and CO_2 for enhanced coalbed methane recovery and carbon dioxide sequestration

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Journal of Natural Gas Chemistry 2008年第1期17卷 29-38页

作者： Basanta Kumar Prusty Central Institute of Mining and Fuel Research Barwa RoadDhanbad-826 001India

Sequestration of CO2 in deep and unmineable coal seams is one of the attractive alternatives to reduce its atmospheric concentration. Injection of CO2 in coal seams may help in enhancing the recovery of coalbed methane. An experimental study has been carried out using coal samples from three different coal seams, to evaluate the enhanced gas recovery and sequestration potential of these coals. The coals were first saturated with methane and then by depressurization some of the adsorbed methane was desorbed. After partial desorption, CO2 was injected into the coals and subsequently they were depressurized again. Desorption of methane after the injections was studied, to investigate the ability of CO2 to displace and enhance the recovery of methane from the coals. The coals exhibited varying behavior of adsorption of CO2 and release of methane. For one coal, the release of methane was enhanced by injection of CO2, suggesting preferential adsorption of CO2 and desorption of methane. For the other two coals, CO2 injection did not produce incremental methane initially, as there was initial resistance to methane release. However with continued CO2 injection, most of the remaining methane was produced. The study suggested that preferential sorption behavior of coal and enhanced gas recovery pattern could not be generalized for all coals.

关键词： coal coalbed methane CO2 injection enhanced coalbed methane CO2 sequestration

Productivity enhancement in multilayered coalbed methane reservoirs by radial borehole fracturing

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Petroleum Science 2022年第6期19卷 2844-2866页

作者： Rui-Yue Yang Gen-Sheng Li Xiao-Zhou Qin Zhong-Wei Huang Jing-Bin Li Mao Sheng Bin Wang State Key Laboratory of Petroleum Resources and Prospecting China University of PetroleumBeijing102249China

coalbed methane(CBM)is an important unconventional natural *** of multilayered CBM reservoir is still facing the challenge of low production *** borehole fracturing,which integrates radial jet drilling and hydraulic fracturing,is expected to create complex fracture networks in multilayers and enhance CBM *** main purpose of this paper is to investigate the mechanisms and efficacy of radial borehole fracturing in increasing CBM production in multiple ***,a two-phase flow and multi-scale 3 D fracture network including radial laterals,hydraulic fractures and face/butt cleats model is established,and embedded discrete fracture model(EDFM)is applied to handle the complex fracture ***,effects of natural-fracture nonuniform distribution are investigated to show the advantages of targeted stimulation for radial borehole ***,two field CBM wells located in eastern Yunnan-western Guizhou,China were presented to illuminate the stimulation efficiency by radial borehole *** results indicated that compared with vertical well fracturing,radial borehole fracturing can achieve higher gas/water daily production rate and cumulative gas/water production,approximately 2 times *** communications to cleats and sweet spots and flexibility in designing radial borehole parameters in different layers so as to increase fracture-network complexity and connectivity are the major reasons for production enhancement of radial borehole ***,the integration of geology-engineering is vital for the decision of radial borehole fracturing designing *** key findings of this paper could provide useful insights towards understanding the capability of radial borehole fracturing in developing CBM and coal-measure gas in multiple-thin layers.

关键词： coalbed methane Multilayered coal beds Radial borehole fracturing Complex fracture networks Cleats distribution

The generalized method for estimating reserves of shale gas and coalbed methane reservoirs based on material balance equation

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Petroleum Science 2022年第6期19卷 2867-2878页

作者： Jun-Tai Shi Yan-Ran Jia Long-Long Zhang Chang-Jiang Ji Guo-Fu Li Xian-Yue Xiong Hong-Xing Huang Xiang-Fang Li Sui-An Zhang State Key Laboratory of Petroleum Resources and Prospecting in China University of Petroleum(Beijing) Beijing102249China coalbed methane Research Center China University of Petroleum(Beijing)Beijing102249China State Key Laboratory of Coal and CBM Co-Mining in Nancun Town Jincheng048012ShanxiChina Petro China coalbed methane Company Limited Beijing100028China China United coalbed methane National Engineering Research Center Co.Ltd Beijing100095China

As the main unconventional natural gas reservoirs,shale gas reservoirs and coalbed methane(CBM)reservoirs belong to adsorptive gas reservoirs,i.e.,gas reservoirs containing adsorbed *** gas and CBM reservoirs usually have the characteristics of rich adsorbed gas and obvious dynamic changes of porosity and permeability.A generalized material balance equation and the corresponding reserve evaluation method considering all the mechanisms for both shale gas reservoirs and CBM reservoirs are *** this work,a generalized material balance equation(GMBE)considering the effects of critical desorption pressure,stress sensitivity,matrix shrinkage,water production,water influx,and solubility of natural gas in water is ***,by converting the GMBE to a linear relationship between two parameter groups related with known formation/fluid properties and dynamic performance data,the straight-line reserve evaluation method is *** using the slope and the y-intercept of this straight line,the original adsorbed gas in place(OAGIP),original free gas in place(OFGIP),original dissolved gas in place(ODGIP),and the original gas in place(OGIP)can be quickly ***,two validation cases for shale gas reservoir and CBM reservoir are conducted using commercial reservoir simulator and the coalbed methane dynamic performance analysis software,***,two field studies in the Fuling shale gas field and the Baode CBM field are *** show that the GMBE and the corresponding straight-line reserve evaluation method are rational,accurate,and effective for both shale gas reservoirs and CBM *** detailed information about reserves of shale gas and CBM reservoirs can be clarified,and only the straight-line fitting approach is used to determine all kinds of reserves without iteration,proving that the proposed method has great advantages compared with other current methods.

关键词： Shale gas coalbed methane Material balance equation Reserve evaluation Dissolved gas Generalized method

An economic evaluation method of coalbed methane resources during the target selection phase of exploration

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Petroleum Science 2015年第4期12卷 705-711页

作者： Dong-Kun Luo Liang-Yu Xia School of Business Administration China University of Petroleum (Beijing)

Because forecasting a development program during the target selection phase of exploration for coalbed methane （CBM） is impossible, the conventional method that relies on a conceptual （or detailed） development pro- gram cannot be used during the economic evaluation of CBM resources. Hence, this study focuses on establishing an economic evaluation model based on the characteristics of the target selection phase. The discounted cashflow method is applied to the construction of the model with the assumption that there is a uniform distribution of produc- tion wells. The computational error generated by the assumption is corrected by introducing a correction factor based on the production profile of single CBM wells. The case study demonstrates that the blocks lacking economic value can be screened out, and the most advantageous targets can be found by computing the resource values in the best- and worst-case scenarios. This technique can help to reduce wasted investments and improve the quality of decision-making in selecting targets for exploration.

关键词： coalbed methane Exploration targetselection Economic evaluation Scenario analysis

Structural Controls on coalbed methane Reservoirs in Faer Coal Mine, Southwest China

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Journal of Earth Science 2013年第3期24卷 437-448页

作者：李明姜波林寿发兰凤娟汪吉林 School of Resource and Earth Science China University of Mining and Technology Department of Earth and Environmental Sciences University of Waterloo School of Resource and Earth Science China University of Mining and Technology Key Laboratory of coalbed methane Resource and Reservoir Formation Process Ministry of EducationChina University of Mining and Technology

Guizhou （贵州） Province, Southwest China, is rich in coalbed methane （CBM） resources, wherein its geological structure is complicated. We discuss the occurrence characteristics of CBM based on CBM borehole test data and geological setting. In combination with the analysis of the regional tectonics, macro-and micro-scopic geological structures and pore size distributions, the structural controls on CBM reservoirs were further discussed from the aspects involving tectonic evolution, structural features, and deformation of coal. The results show that the CBM enrichment was mainly controlled by the regional tectonic subsidence and weak structural deformation on coal reservoirs after coal formation. The Yangmeishu （杨梅树） syncline and topography are the main controlling factors to the current distribution pattern of CBM, which is higher in the north than the south and trending toward the NE direction. Normal faults and fractures can be divided into open, closed, and occluded types. The open type reduces both gas content and methane concentration of nearby coal seams. The closed type causes the decrease of gas content, while methane concentration is still high. The occluded type fail to reduces gas content, and even results in the enrichment of CBM in small areas near fault. Moderate brittle deformation can improve the pore structure and development of structural fracture of coal *** structural coals with well-developed fractures and relatively uniformly distributed pore structures are common in the Faer （发耳） coal mine, which are favorable for the production of CBM.

关键词： coalbed methane structure fault tectonically deformed coal Faer coal mine.

Reasonable start time of carbon dioxide injection in enhanced coalbed methane recovery involving thermal-hydraulic-mechanical couplings

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Frontiers of Earth Science 2023年第3期17卷 832-843页

作者： Chaojun FAN Lei YANG Bin XIAO Lijun ZHOU Haiou WEN Hao SUN College of Mining Liaoning Technical UniversityFuxin 123000China College of Safety Science and Engineering Liaoning Technical UniversityHuludao 125105China

Injection of gas (CO_(2)) into coal seams is an effective method to benefit from both CO_(2) geological storage and coalbed methane recovery. Based on the dual pore structure of coal mass, and the Weibull distribution of fracture permeability, a menmal-hydraulic-mechanical (THM) coupling mathematical model is proposed involving the non-isothermal adsorption of binary gases, dynamic gas diffusion between matrix and fractures, multiphase seepage, coal deformation, heat conduction and heat convection. This mathematical model is applied to study the process of CO_(2)-enhanced coalbed methane recovery (CO_(2)-ECBM). Results show that the CH4 content of CO_(2)-ECBM in coal seam decreases significantly when compared with that of regular drainage, and decreases rapidly in the early stage but slowly in the later stage. Coal seam permeability evolution is triggered by changes in gas adsorption/desorption, temperature and effective stress. For regular drainage, the early permeability shows a decreasing trend dominated by the increase of effective stress, while the later permeability shows an increasing trend dominated by the CH4 desorption caused shrinkage of coal matrix. For CO_(2)-ECBM, the permeability in coal seam generally shows a downward trend due to both matrix swelling induced by gas adsorption and thermal expansion, particularly near injection well. There appears an increased and delayed peak production rate of CH4. The CH4 production rate of CO_(2)-ECBM is always higher than that of regular drainage. The CH4 cumulative production and CO_(2) cumulative storage linearly increase with time, and the CH4 cumulative production of CO_(2)-ECBM increased by 39.2% in the duration of 5000 d compared with regular drainage. Reasonable CO_(2) injection starting time can overcome the issue of early CO_(2) breakthrough and ineffective increase of CH4 production. In the studied case, the optimal injection starting time is 2500 d. Compared with the simultaneous CH4 extraction and CO_

关键词： CO_(2)sequestration coalbed methane reasonable injection start time thermo-hydro-mechanical coupling model numerical simulation

Methods for simultaneously evaluating reserve and permeability of undersaturated coalbed methane reservoirs using production data during the dewatering stage

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Petroleum Science 2020年第4期17卷 1067-1086页

作者： Jun-Tai Shi Jia-Yi Wu Zheng Sun Zhi-Hua Xiao Cheng Liu Kamy Sepehrnoori State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum BeijingNo.18Fuxue RoadChangping DistrictBeijing 102249China MOE Key Laboratory of Petroleum Engineering China University of Petroleum BeijingNo.18Fuxue RoadChangping DistrictBeijing 102249China PetroChina coalbed methane Company Limited Beijing 100028China PetroChina Zhejiang Oil Field Company Limited Hangzhou 310023China The University of Texas AustinTX 78712USA

In this work,a flowing material balance equation(FMBE) is established for under saturated coalbed methane(CBM) reservoirs,which considers immobile free gas expansion effect at the dewatering *** on the established FMBE,five straight-line methods are proposed to determine the control area,initial water reserve,initial free gas reserve,initial adsorbed gas reserve,original gas in place,as well as permeability at the same ***,the proposed FMBE methods for undersaturated CBM reservoirs are validated against a reservoir simulation software with and without considering free gas ***,the proposed methods are applied in a field case when considering free gas expansion *** cases show that the straight-line relationships for the proposed five FMBE methods are excellent,and good agreements are obtained among the actual reserves and permeabilities and those evaluated by the proposed five FMBE methods,indicating the proposed five FMBE methods are effective and rational for CBM *** show that a small amount of free gas will result in a great deviation in reserve evaluation;hence,the immobile free gas expansion effect should be considered when establishing the material balance equation of undersaturated CBM reservoirs at the dewatering stage.

关键词： coalbed methane OGIP Permeability evaluation Flowing material balance equation Gas expansion

Drilling and completion technologies of coalbed methane exploitation: an overview

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International Journal of Coal Science & Technology 2022年第5期9卷 1-31页

作者： Tianshou Ma Jinhua Liu Jianhong Fu Bisheng Wu State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChengdu 610500SichuanChina State Key Laboratory of Hydroscience and Engineering Department of Hydraulic EngineeringTsinghua UniversityBeijing 100084China

coalbed methane(CBM)drilling and completion technologies(DCTs)are signifcant basis for achieving efcient CBM exploration and *** of CBM reservoirs vary in diferent regions around the world,thereby,it is crucial to develop,select and apply the optimum DCTs for each diferent CBM *** paper frstly reviews the development history of CBM DCTs throughout worldwide and clarifes its overall development ***,diferent well types and its characteristics of CBM exploitation are summarized,and main application scopes of these well types are also ***,the key technologies of CBM drilling(directional drilling tools,measurement while drilling,geo-steering drilling,magnetic guidance drilling,underbalanced drilling and drilling fuids),and the key technologies of CBM completion(open-hole,cavity and under-ream completion,cased-hole completion,screen pipe completion and horizontal well completion)are summarized and analyzed,it is found that safe,economic and efcient development of CBM is inseparable from the support of advanced ***,based on the current status of CBM development,the achievements,existing challenges and future prospects are summarized and discussed from the perspective of CBM DCTs.

关键词： coalbed methane CBM Exploitation Drilling Completion Horizontal well L/U/V-shaped well Multilateral well