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Optimization design of multi-gathering mode for the surface system in coalbed methane field

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Petroleum 2023年第2期9卷 237-247页

作者： Jun Zhou Tiantian Fu Kunyi Wu Yunxiang Zhao Lanting Feng Petroleum Engineering School Southwest Petroleum UniversityChengduChina Research Institute of Gathering and Transportation Engineering Technology PetroChina Southwest Oil&Gas Field CompanyChengduChina Pipechina Southwest Pipeline Company ChengduChina

As a potential resource for emerging clean energy with abundant reserves,coalbed methane(CBM)has risen rapidly in recent years,and the construction of rational and economical CBM gathering system plays a vital role in the development of the oil and gas industry.At present,there is no literature that considers the optimization of the multi-gathering mode of coalbed methane pipe network system.Due to the complexity and high investment,this paper establishes a unified mixed-integer nonlinear programming model to determine the gathering modes(including liquified natural gas,compressed natural gas,and gas gathering station)of gathering system to reduce the cost of coalbed methane collection and export.The objective function is the maximization of total profit during the period of the whole project,and such constraints,like network structure,facility number,location,node flow balance,capacity and variable value,are taken into consideration.The solution strategy and heuristic algorithm is proposed and verified by the field data from Shanxi province(China).The results show that the model can solve the problem for optimization design of the surface system in complicated CBM fields.

关键词： coalbed methane Multi-gathering mode Optimization Pipeline network

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 gas.Exploitation of multilayered CBM reservoir is still facing the challenge of low production rate.Radial borehole fracturing,which integrates radial jet drilling and hydraulic fracturing,is expected to create complex fracture networks in multilayers and enhance CBM recovery.The main purpose of this paper is to investigate the mechanisms and efficacy of radial borehole fracturing in increasing CBM production in multiple layers.First,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 networks.Then,effects of natural-fracture nonuniform distribution are investigated to show the advantages of targeted stimulation for radial borehole fracturing.Finally,two field CBM wells located in eastern Yunnan-western Guizhou,China were presented to illuminate the stimulation efficiency by radial borehole fracturing.The 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 higher.Targeted 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 fracturing.Furthermore,the integration of geology-engineering is vital for the decision of radial borehole fracturing designing scheme.The 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.Shale 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 necessary.In 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 established.Then,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 proposed.By 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 calculated.Third,two validation cases for shale gas reservoir and CBM reservoir are conducted using commercial reservoir simulator and the coalbed methane dynamic performance analysis software,respectively.Finally,two field studies in the Fuling shale gas field and the Baode CBM field are presented.Results show that the GMBE and the corresponding straight-line reserve evaluation method are rational,accurate,and effective for both shale gas reservoirs and CBM reservoirs.More 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

Research progress on isotopic fractionation in the process of shale gas/coalbed methane migration

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Petroleum Exploration and Development 2022年第5期49卷 1069-1084页

作者： LI Wenbiao LU Shuangfang LI Junqian WEI Yongbo ZHAO Shengxian ZHANG Pengfei WANG Ziyi LI Xiao WANG Jun Sanya Offshore Oil&Gas Research Institute Northeast Petroleum UniversitySanya 572025China Key Laboratory of Continental Shale Hydrocarbon Accumulation and Efficient Development Ministry of EducationNortheast Petroleum UniversityDaqing 163318China School of Geosciences China University of Petroleum(East China)Qingdao 266580China Exploration and Development Research Institute of Daqing Oilfield Co.Ltd. Daqing 163712China Shale Gas Research Institute of PetroChina Southwest Oil&Gasfield Company Chengdu 610051China College of Earth Science and Engineering Shandong University of Science and TechnologyQingdao 266590China

The research progress of isotopic fractionation in the process of shale gas/coalbed methane migration has been reviewed from three aspects: characteristics and influencing factors, mechanism and quantitative characterization model, and geological application. It is found that the isotopic fractionation during the complete production of shale gas/coalbed methane shows a four-stage characteristic of “stable-lighter-heavier-lighter again”, which is related to the complex gas migration modes in the pores of shale/coal. The gas migration mechanisms in shale/coal include seepage, diffusion, and adsorption/desorption. Among them, seepage driven by pressure difference does not induce isotopic fractionation, while diffusion and adsorption/desorption lead to significant isotope fractionation. The existing characterization models of isotopic fractionation include diffusion fractionation model, diffusion-adsorption/desorption coupled model, and multi-scale and multi-mechanism coupled model. Results of model calculations show that the isotopic fractionation during natural gas migration is mainly controlled by pore structure, adsorption capacity, and initial/boundary conditions of the reservoir rock. So far, the isotope fractionation model has been successfully used to evaluate critical parameters, such as gas-in-place content and ratio of adsorbed/free gas in shale/coal etc. Furthermore, it has shown promising application potential in production status identification and decline trend prediction of gas well. Future research should focus on:(1) the co-evolution of carbon and hydrogen isotopes of different components during natural gas migration,(2) the characterization of isotopic fractionation during the whole process of gas generation-expulsion-migration-accumulation-dispersion, and(3) quantitative characterization of isotopic fractionation during natural gas migration in complex pore-fracture systems and its application.

关键词： shale gas coalbed methane diffusive fractionation adsorption/desorption fractionation isotope fractionation model natural gas migration

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_(2) injection, the CH4 cumulative production of

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

Multi-stage gas diffusion and its implications for the productivity of coalbed methane in the southern Qinshui Basin, north China

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Frontiers of Earth Science 2023年第1期17卷 109-120页

作者： Hui WANG Yanbin YAO Zhentao LI Yanhui YANG Junjie YI Yongkai QIU Shengqiang ZHOU School of Energy Resource China University of GeosciencesBeijing 100083China Coal Reservoir Laboratory of National Engineering Research Center of CBM Development&Utilization China University of GeosciencesBeijing 100083China State Key Laboratory of Organic Geochemistry Guangzhou Institute of GeochemistryChinese Academy of SciencesGuangzhou 510640China PetroChina Huabei Oilfield Company Renqiu 062552China Institute of Mineral Resources Research Beijing 101300China

The behavior of coalbed methane(CBM)diffusion considerably influences gas productivity.Based on the multi-porous diffusion model and on-site CBM desorption data of coal cores,the behavior of CBM diffusion and its implications on the gas productivity of No.3 coal seam in the southern Qinshui Basin(SQB)were elaborately analyzed.Results indicate that CBM diffusion of No.3 coal seam demonstrates noticeable three-stage characteristics,including the fast diffusion,transitional diffusion,and slow diffusion stages.During the gas diffusion process,the gas content and/or the degree of developed pores and fractures/cleats in coal seams can affect the desorption of CBM and the amount of diffused CBM by influencing the changes in gas pressure in pores,thus controlling the behavior of gas diffusion in different stages.Because gas content and the developed degree of pores and fractures/cleats are closely associated with the deformation degree of the coal seams,variably deformed coal seams exhibit unique characteristics of gas diffusion.The low-deformation degree of the coal seams have a relatively uniform distribution of gas production over the history of a well.By contrast,the moderate-deformation degree of the coal seams have a relatively high rate and amount of gas diffusion in the fast and transitional diffusion stages,producing most of the gas in the early-to-intermediate stages of the wells.Finally,the high-deformation degree of the coal seams has a high rate and amount in the fast diffusion stage,indicating that most of the production stage occurs during the early stage of the gas production history of a well.In summary,the behavior of gas diffusion can be used for predicting gas production potential.

关键词： coalbed methane gas diffusion CBM production coal deformation Qinshui Basin

Stress sensitivity of coal reservoir and its impact on coalbed methane production in the southern Qinshui Basin, north China

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Frontiers of Earth Science 2023年第1期17卷 4-17页

作者： Huimin JIA Yidong CAI Qiujia HU Cong ZHANG Feng QIU Bin FAN Chonghao MAO CBM Exploration and Development Branch PetroChina Huabei Oilfeld CompanyChangzhi 046000China School of Energy Resources China University of GeosciencesBeijing 100083China

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 m

关键词： coalbed methane stress sensitivity curvature stages division drainage

A method for identifying coalbed methane co-production interference based on production characteristic curves: A case study of the Zhijin block, western Guizhou, China

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Petroleum Exploration and Development 2022年第5期49卷 1126-1137页

作者： GUO Chen QIN Yong YI Tongsheng CHEN Zhenlong YUAN Hang GAO Junzhe GOU Jiang College of Geology and Environment Xi'an University of Science and TechnologyXi'an 710054China Shaanxi Provincial Key Laboratory of Geological Support for Coal Green Exploitation Xi'an 710054China Geological Research Institute for Coal Green Mining Xi'an University of Science and TechnologyXi'an 710054China Key Laboratory of CBM Resources and Reservoir Formation Process Ministry of EducationChina University of Mining and TechnologyXuzhou 221116China Guizhou Bureau of Coal Geological Exploration Guiyang 550008China East China Oil&Gas Company SinopecNanjing 210011China

Efficient detection of coalbed methane(CBM) co-production interference is the key to timely adjusting the development plan and improving the co-production efficiency. Based on production data of six typical CBM co-production wells in the Zhijin block of western Guizhou Province, China, the production characteristic curves, including production indication curve, curve of daily water production per unit drawdown of producing fluid level with time, and curve of water production per unit differential pressure with time have been analyzed to explore the response characteristics of co-production interference on the production characteristic curves. Based on the unit water inflow data of pumping test in coal measures, the critical value of in-situ water production of the CBM wells is 2 m^(3)/(d·m). The form and the slope of the initial linear section of the production indication curves have clear responses to the interference, which can be used to discriminate internal water source from external water source based on the critical slope value of 200 m^(3)/MPa in the initial linear section of the production indication curve. The time variation curves of water production per unit differential pressure can be divided into two morphological types: up-concave curve and down-concave curve. The former is represented by producing internal water with average daily gas production greater than 800 m^(3)/d, and the latter produces external water with average daily gas production smaller than 400 m^(3)/d. The method and critical indexes for recognition of CBM co-production interference based on the production characteristic curve are constructed. A template for discriminating interference of CBM co-production was constructed combined with the gas production efficiency analysis, which can provide reference for optimizing co-production engineering design and exploring economic and efficient co-production mode.

关键词： coalbed methane multi-seam co-production interlayer interference production indication curve external water internal water discrimination template

Evaluation of infill well pattern based on the dynamic change of reservoirs during coalbed methane development

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Frontiers of Earth Science 2023年第3期17卷 646-660页

作者： Qian ZHANG Shuheng TANGI Songhang ZHANG Xinlu YAN Kaifeng WANG Tengfei JIA Zhizhen WANG School of Energy Resources China University of Geosciences(Beijing)Beijing 100083China Coal Reservoir Laboratory of National Engineering Research Center of CBM Development&Utilization Beijing 100083China Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering Beijing 100083China College of Mining Technology Taiyuan University of TechnologyTaiyuan 030024China

With the deepening of coalbed methane(CBM)exploration and development,the problem of low gas production has gradually become one of the main factors restricting the development of the CBM industry in China.Reasonable well pattern deployment can improve the productivity of CBM wells and reduce the cost of production,while the reservoir changes of CBM wells play a important role for well pattern infilling.In this study,the dynamic characteristics of the average reservoir pressure(ARP),permeability,and drainage radius during the development process of CBM wells are systematically analyzed,and predicted the production changes of well groups before and after infilling wells in combination with the characteristics of reservoir changes.The results show that the high gas production wells have a larger pressure drop,long drainage radius,and a large increase in permeability.On the contrary,low gas production wells are characterized by small drainage radius,damaged permeability and difficult to recover.The productivity of infilled horizontal wells is predicted for two well groups with different productivity and reservoir dynamic characteristics.After infilling wells,the production of current wells has increased at different degrees.It is predicted that the average gas production of low gas production well group H1 and middle gas production well group H2 will increase 1.64 and 2.09 times respectively after 3000 days production simulation.In addition,the pressure interference between wells has increased significantly,and the overall gas production of the well group has greatly increased.Infill wells can achieve better development results in areas with superior CBM resources,recoverable reservoir permeability,and small drainage radius during the early production process.The research results provide a reference for the later infill adjustment of CBM well patterns in the study area.

关键词： well pattern optimization reservoir dynamic variation infill well deployment coalbed methane Qinshui Basin