Optimization strategy and procedure for coal bed methane separation

Coal bed methane （CBM） has a huge potential to be purified to relieve the shortage of natural gas meanwhile to weaken the greenhouse effect. This paper proposed an optimal design strategy for CBM to obtain an integrated process configuration consisting of three each single separation units, membrane, pressure swing absorption, and cryogenics. A superstructure model was established including all possible network configurations which were solved by MINLP. The design strategy optimized the separation unit configuration and operating conditions to satisfy the target of minimum total annual process cost. An example was presented for the separation of CH4/N2 mixtures in coal bed methane （CBM） treatment. The key operation parameters were also studied and they showed the influence to process configurations.

Prediction of geotemperatures in coal-bearing strata and implications for coal bed methane accumulation in the Bide-Santang basin,western Guizhou,China

The geothermal fields of coal-bearing strata have become a key topic in geological research into coal and coal bed methane(CBM).Based on temperature data from 135 boreholes that penetrate the Upper Permian coal-bearing strata in the Bide-Santang basin,western Guizhou,the precisions of geothermal predictions made using a geothermal gradient model and a gray sequence GM(1,1)model are analyzed and compared.The results indicate that the gray sequence GM(1,1)model is more appropriate for the prediction of geothermal fields.The GM(1,1)model is used to predict the geothermal field at three levels with depths of 500,1000,and 1500 m,as well as within the No.6,No.16,and No.27 coal seams.The results indicate that the geotemperatures of the 500 m depth level are between 21.0 and 30.0°C,indicating no heat damage;the geotemperatures of the 1000 m depth level are between 29.4 and 44.7°C,indicating the first level of heat damage;and the geotemperatures of the 1500 m depth level are between35.6 and 63.4°C,indicating the second level of heat damage.The CBM contents are positively correlated with the geotemperatures of the coal seams.The target area for CBM development is identified.

A continuous and high-efficiency process to separate coal bed methane with porous ZIF-8 slurry:Experimental study and mathematical modelling

Coal bed methane has been considered as an important energy resource.One major difficulty of purifying coal bed methane comes from the similar physical properties of CH_4 and N_2.The ZIF-8/water-glycol slurry was used as a medium to separate coal bed methane by fluidifying the solid adsorbent material.The sorption equilibrium experiment of binary mixture(CH_4/N_2)and slurry was conducted.The selectivity of CH_4 to N_2 is within the range of 2-6,which proved the feasibility of the slurry separation method.The modified Langmuir equation was used to describe the gas-slurry phase equilibrium behavior,and the calculated results were in good agreement with the experimental data.A continuous absorption-adsorption and desorption process on the separation of CH_4/N_2 in slurry is proposed and its mathematical model is also developed.Sensitivity analysis is conducted to determine the operation conditions and the energy performance of the proposed process was also evaluated.Feed gas contains 30 mol%of methane and the methane concentration in product gas is 95.46 mol%with the methane recovery ratio of 90.74%.The total energy consumption for per unit volume of product gas is determined as 1.846 kWh Nm^(-3).Experimental results and process simulation provide basic data for the design and operation of pilot and industrial plant.

Seismic studies of coal bed methane content in the west coal mining area of Qinshui Basin

The coal bed methane content(CBMC)in the west mining area of Jincheng coalfield,southeastern Qjnshui Basin,is studied based on seismic data and well-logs together with laboratory measurements.The results show that the Shuey approximation has better adaptability according to the Zoeppritz equation result;the designed fold number for an ordinary seismic data is sufficient for post-stack data but insufficient for pre-stack data regarding the signal to noise ratio(SNR).Therefore a larger grid analysis was created in order to improve the SNR.The velocity field created by logging is better than that created by stack velocity in both accuracy and effectiveness.A reasonable distribution of the amplitude versus offset(AVO)attributes can be facilitated by taking the AVO response from logging as a standard for calibrating the amplitude distribution.Some AVO attributes have a close relationship with CBMC.The worst attribute is polarization magnitude,for which the correlation coefficient is 0.308;and the best attribute is the polarization product from intercept,of which the correlation coefficient is-0.8136.CBMC predicted by AVO attributes is better overall than that predicted by direct interpolation of CBMC;the validation error of the former is 14.47%,which is lower than that of the latter 23.30%.CBMC of this area ranges from2.5 m^3/t to 22 m^3/t.Most CBMC in the syncline is over 10m^3/t,but it is below 10m^3/t in the anticline;on the whole,CBMC in the syncline is higher than that in anticline.

Theories and techniques of coal bed methane control in China

Coal bed methane control with low permeability is a hot issue at present. The current status of coal bed methane control in China is introduced. The government-support policies on coal bed methane control are presented. This paper proposes the theories of methane control in depressurized mining, including methane extraction in depressurized mining, simultaneous mining technique of coal and methane without coal pillar, and circular overlying zone for high-efficiency methane extraction in coal seams with low permeability. The techniques of methane control and related instruments and equipments in China are introduced. On this basis, the problems related to coal bed methane control are addressed and further studies are pointed out.

Some parameters of coal methane system that cause very slow release of methane from virgin coal beds(CBM)

In some worldwide hard coal basins recovery of methane from virgin coal beds is difficult. In general,mentioned difficulties are related to geo-mechanical, petrographical and physical-chemical properties of coals in question, occurring for example in the Bowen Basin(Australia) or the Upper Silesian Coal Basin(Poland). Among numerous properties and parameters, the following are very essential: susceptibility of coal beds to deformation connected with coal stress state change and contemporary shrinkage of the coal matrix during methane desorption. Those adverse geo-mechanical and physical-chemical effects are accompanied by essential change of the porous coal structure, which under these disadvantageous conditions is very complex. This study aims to show difficulties, which occur in phase of recognition of the methane-reach coal deposit. Volume absorbed methane(not surface adsorbed) in sub-micropores having minimal size comparable with gas molecule diameter must possess energy allowing separation of the nodes and methane release to micropores.

Productivity enhancement in multilayered coalbed methane reservoirs by radial borehole fracturing

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.

The control of coal mine gas and coordinated exploitation of coal bed methane in China

Based on the characteristics of the coalfield geology and the distribution of coalbed methane (CBM) in China,the geological conditions for exploiting the CBM and drainingthe coal mine gas were analyzed,as well as the characteristics of CBM production.Bycomparing the current situation of CBM exploitation in China with that in the United States,the current technology and characteristics of the CBM exploitation in China were summarizedand the major technical problems of coal mine gas control and CBM exploitationanalyzed.It was emphasized that the CBM exploitation in China should adopt the coalmine gas drainage method coordinated with coal mine exploitation as the main model.Itwas proposed that coal mine gas control should be coordinated with coal mine gas exploitation.The technical countermeasure should be integrating the exploitation of coal andCBM and draining gas before coal mining.

A Comprehensive Appraisal on the Characteristics of Coal-Bed Methane Reservoir in Turpan-Hami Basin

The rich coal-bed methane resources in the Turpan-Hami Basin are mainly located in the Shisanjianfang,Hami,Shanshan,Sha'erhu,Kekeya,Kerjian,Aidinghu inclines and the Dananhu coal-bed methane reservoirs. The big-ger coal-bed reservoirs are sitting at a depth of less than 1500 m. The coalbed methane generation,storage and confin-ing conditions of the Turpan-Hami basin can be indicated by eight key parameters. They are coal-bed thickness,coal rank,missing period,permeability,Langmuir volume,rock covering ability,structural confinement and hydrodynamic sealing environment. These parameters constitute a comprehensive appraisal index system of the coal-bed methane res-ervoir characteristics of the Turpan-Hami basin. In these parameters,the missing period of coal-bed methane is indi-cated by a stratum missing intensity factor. It reflects the relative exposure period of coal series. The results of a fuzzy comprehensive judgment showed that the Shisanjianfang coal-bed methane reservoir has the best prospects for exploita-tion and the Sha'erhu,Shanshan,Hami coal-bed methane reservoirs are next in line.

Evaluation of coal bed methane content using BET adsorption isotherm equation

Coal bed methane is unconventional raw natural gas stored in coal seam with considerable reserves in China.In recent years,as the coal bed methane production,the safety and the use of resources have been paid more attentions.Evaluating coal bed methane content is an urgent problem.A BET adsorption isotherm equation is used to process the experimental data.The various parameters of BET equation under different temperatures are obtained;a theoretical gas content correction factor is proposed,and an evaluation method of actual coal bed methane is established.

The experiment study on slippage effect of the coal-bed methane transfusion

When the gas flow in the compact porous medium at low speed,it has slippage effect which is caused by the gas molecular collision whit the solidskeleton.Using the gas transfusion slippage effect at researching the coal bed transfusion rule,established the transfusion mathematical model of the coal bed which had considered the slippage effect. Observing the influence of the different toencircle presses,the different hole press and the different actual stress to the coal bed by using the three-axles permeameter.Thus sum- marized the transfusion rule of the coal bed.The experiment indicates that the bigger of the surrounding pressure,the more obvious of the slippage effect.At the same condition of axial pressure and the surrounding pressure,with the increase of the hole pressure,the coal permeability became bigger and then smaller.The coal body effective tress and the permeability curve nearly also has the same change tendency.Thus we can draws the conclusion that the transfusion of the gas in the coal bed generally has the slippage effect.

Adsorption behavior of carbon dioxide and methane in bituminous coal:A molecular simulation study

The adsorption behavior of CO_2, CH_4 and their mixtures in bituminous coal was investigated in this study. First, a bituminous coal model was built through molecular dynamic(MD) simulations, and it was confirmed to be reasonable by comparing the simulated results with the experimental data. Grand Canonical Monte Carlo(GCMC)simulations were then carried out to investigate the single and binary component adsorption of CO_2 and CH_4with the built bituminous coal model. For the single component adsorption, the isosteric heat of CO_2 adsorption is greater than that of CH_4 adsorption. CO_2 also exhibits stronger electrostatic interactions with the heteroatom groups in the bituminous coal model compared with CH_4, which can account for the larger adsorption capacity of CO_2 in the bituminous coal model. In the case of binary adsorption of CO_2 and CH_4mixtures, CO_2 exhibits the preferential adsorption compared with CH_4 under the studied conditions. The adsorption selectivity of CO_2 exhibited obvious change with increasing pressure. At lower pressure, the adsorption selectivity of CO_2 shows a rapid decrease with increasing the temperature, whereas it becomes insensitive to temperature at higher pressure. Additionally, the adsorption selectivity of CO_2 decreases gradually with the increase of the bulk CO_2 mole fraction and the depth of CO_2 injection site.

Research regarding coal-bed wellbore stability based on a discrete element model

Wellbore instability is a key problem restricting efficient production of coal-bed methane. In order to perform thorough and systematic research regarding coal-bed wellbore stability problems, a new discrete element model which fully considers the features of cleat coal-beds is established based on the Kirsch equation. With this model, the safe pipe tripping speed, drilling fluid density window and coal- bed collapse/fracture pressure are determined; in addition, the relationships between pipe tripping speed and pipe size, cleat size, etc. and wellbore stability are analyzed in the coal-bed drilling and pipe tripping processes. The case studies show the following results： the wellbore collapses （collapse pressure： 4.33 MPa） or fractures （fracture pressure： 12.7 MPa） in certain directions as a result of swab or surge pressure when the pipe tripping speed is higher than a certain value; the cleat face size has a great influence on wellbore stability, and if the drilling fluid pressure is too low, the wellbore is prone to collapse when the ratio of the face cleat size to butt cleat size is reduced; however, if the drilling fluid pressure is high enough, the butt cleat size has no influence on the wellbore fracture; the factors influencing coal-bed stability include the movement length, pipe size, borehole size.

Early Opportunity of CO_2 Storage in Coal Bed of China

A study to identify potential early opportunities for CO2 storage in coal bed has been performed. CO2-ECBM can enhances the recovery of coalbed methane,and also store CO2 in coal for geological time.CO2-ECBM is an effective measure for CO2 mitigation,and also enhance the recovery of coalbed methane that can reduce the cost of CO2 geological storage.The evaluation index system of feasibility

Assessment of parameters effectiveness in the reserve estimation methods applicable to coal bed methane reservoirs

The reserve estimation of coal bed methane(CBM)reservoirs is ascertained through the analytical methods(volumetric method,material balance equation and decline curve analysis).However,the adoption of reserve estimation methods depends on exploration stage and availability of the required parameters.This study deals with the analytical assessment of parameters that participate in effecting the reserve estimation of CBM reservoirs through the analytical techniques.The accurate measurement challenges always exist for the parameters which participate in the reserve estimation of the conventional and unconventional reservoirs because of the inclusion of limitations while measurement.Therefore,the impact of that measurement challenge must be assessed.The study specifies the impact of parametric change on the reserve estimation of CBM reservoirs so that the degree of parametric effectiveness is analyzed.Uncertain values are adopted which are associated during the evaluation of input parameters for each method to determine the overall impact on potential of CBM reserves.Results reveal that change in specific parameters considering each method provide relatively more effect on estimation of reserves.Thus,the measurement of parameters must be done accurately for assessing reserves of CBM reservoirs based on available methods.

碳中和目标下中国天然气工业进展、挑战及对策

天然气在21世纪中叶将迈入“鼎盛期”,“天然气时代”正在到来。回顾全球天然气工业历程,梳理美国页岩革命启示,总结中国天然气发展历史与成果进展,分析天然气在能源绿色低碳转型中的地位与挑战,提出当前和未来中国天然气工业的发展对策。中国天然气工业经历了起步、增长、跨越3个发展阶段,已成为世界第4大天然气生产国与第3大消费国;天然气勘探开发理论技术取得重大成就,为储量产量规模增长提供了重要支撑。碳中和目标下,推动绿色可持续发展,天然气工业发展挑战与机遇并存。天然气低碳优势显著,“气电调峰”助力新能源发展;同时,开采难度与成本加大等问题更突出。为保障国家能源安全,实现经济社会与生态环境和谐共生,碳中和进程中,立足“统筹布局、科技创新;多能互补、多元融合;灵活高效、优化升级”,完善产供储销体系建设,加速推动天然气工业发展:①加大天然气勘探开发力度,规划部署重点勘探开发领域,突破关键理论,强化技术攻关,持续支撑增储上产;②推进天然气绿色创新发展,突破新技术,拓展新领域,融合新能源;③优化天然气供需转型升级,加大管道气、液化天然气布局和地下储气库建设,建立储备体系,提升应急调节能力和天然气一次能源消费比例,助力能源消费结构转型,实现资源利用低碳化、能源消费清洁化。

非常规油气田节能技术综述

双碳背景下,国家能源安全战略地位高度空前提升。油气田企业作为传统化石能源企业,其绿色低碳发展势在必行。油气田节能技术的发展是“双碳”目标得以实现的重要支撑。文中通过常规油气田节能技术在非常规油气田的适应性分析,结合非常规油气田实际生产特点和工况,按照页岩油、致密油、页岩气、致密气、煤层气等,分类分系统梳理总结非常规油气田地面生产节能技术和典型案例。结合能源管控推进以及油气田与新能源融合绿色低碳发展等总体趋势,提出未来非常规油气田节能技术的发展方向。

海孜煤矿深部勘查区中组煤层气储层物性特征分析

【目的】煤层气储层的物性特征是进行煤层气开发研究的关键因子。【方法】重点对海孜煤矿深部勘探区域中组煤储层的物性参数进行调查,以对井田内中组煤储层物性特征进行研究。【结果】研究表明,煤层的物性特征适宜开采,其中有机显微组分占优,无机显微组分次之。该煤层含气量多,虽然煤层渗透率相对较小,但符合煤层气开采条件。煤层开采时的吸附作用一般,但有利于煤层气储集和缩短煤层气的开发周期。【结论】研究结果可为该研究区煤层气抽采提供可靠的技术参考。

低浓度含氧煤层气净化控制系统设计

低浓度含氧煤层气直接含氧液化精馏制液化天然气(LNG),在充分利用低浓度煤层气的同时又避免了煤矿瓦斯气直接排放造成的大气污染。首先,分析了含氧煤层气制LNG工艺中净化工段的工艺流程,结合工艺要求设计了可靠的控制系统。然后,根据低浓度含氧煤层气净化控制的工艺要求和系统规模,构建了分布式控制系统(DCS)的总体架构。在此基础上进行了硬件系统功能的选型及配置,以及对DCS软件的组态设计。最后,实现了DCS在工程实例中的一体化应用。该系统的应用提高了生产效率和产品质量,为工艺流程的稳定运行提供了安全保障。