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.

Coalbed Methane-bearing Characteristics and Reservoir Physical Properties of Principal Target Areas in North China

The coalbed methane (CBM) resources in North China amounts up to 60% of total resources in China. North China is the most important CBM accumulation area in China. The coal beds of the Upper Paleozoic Taiyuan and Shanxi formations have a stable distribution. The coal reservoir of target areas such as Jincheng, Yanquan-Shouyang, Hancheng, Liulin, etc. have good CBM-bearing characteristics, high permeability and appropriate reservoir pressure, and these areas are the preferred target areas of CBM developing in China. The coal reservoirs of Wupu, Sanjiaobei, Lu'an, Xinmi, Anyang-Hebi, Jiaozuo, Xinggong and Huainan also have as good CBM-bearing characteristics, but the physical properties of coal reservoirs vary observably. So, further work should be taken to search for districts with high pressure, high permeability and good CBM-bearing characteristics. Crustal stresses have severe influence on the permeability of coal reservoirs in North China. From west to east, the crustal stress gradient increases, while the coal reservoirs permeability decreases.

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.

New Progress on the Coal Fines Affecting the Development of Coalbed Methane

Objective The production of coal fines is very common in the development of coalbed methane（CBM）in the eastern margin of the Ordos Basin,China.A large amount of produced coal fines seriously affect the productivity of CBM wells（Wei Yingchun et al.,2013）.Therefore,the production problems of CBM wells caused by coal fines have attracted extensive attention.

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.

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.

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.

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.

Characteristics of dissolved inorganic carbon in produced water from coalbed methane wells and its geological significance

Based on long-term dynamic tracing of dissolved inorganic carbon(DIC)and stable carbon isotope(δ13CDIC)in produced water from 20 coalbed methane(CBM)wells in western Guizhou,the spatial-temporal dynamic variations ofδ13CDIC of the GP well group produced in multi-layer commingled manner were analyzed,and the relationship between the value ofδ13CDIC and CBM productivity was examined.The produced water samples of typical wells in the GP well group were amplified and sequenced using 16S rDNA,and a geological response model ofδ13CDIC in produced water from CBM wells with multi-coal seams was put forward.The research shows that:δ13CDIC in produced water from medium-rank coal seams commonly show positive anomalies,the produced water contains more than 15 species of methanogens,and Methanobacterium is the dominant genus.The dominant methanogens sequence numbers in the produced water are positively correlated withδ13CDIC,and the positive anomaly of v is caused by reduction of methanogens,and especially hydrogenotrophic methanogens.Vertical segmentation of sedimentary facies and lithology in stratum with multi-coal seams will result in permeability and water cut segmentation,which will lead to the segmentation ofδ13CDIC and archaea community in produced water,so in the strata with better permeability and high water cut,theδ13CDIC of the produced water is abnormally enriched,and the dominant archaea is mainly Methanobacterium.In the strata with weak permeability and low water cut,theδ13CDIC of the produced water is small,and the microbial action is weak.The shallow layer close to the coal seam outcrop is likely to be affected by meteoric precipitation,so theδ13CDIC of the produced water is smaller.The geological response model ofδ13CDIC in produced water from multi-coal seams CBM wells in the medium-rank coal reveals the geological mechanism and microbial action mechanism of theδ13CDIC difference in the produced water from the multi-coal seams CBM wells.It also provides effective geochemical evidence for the superimposed fluid system controlled by sedimentary facies,and can also be used for the contribution analysis of the produced gas and water by the multi-layer CBM wells.

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.

Coalbed Methane Potential in the Basin Guardo-Barruelo (North Spain)

Coal during its carbonization process produces a gas, which, mainly formed by methane, can be used. The use of CBM (Coal bed methane) as an energetic resource is not much known in Spain. This work is the first step to enhance the development of this resource in Castilla y León Guardo-Barruelo basin. A review of the state of the art is introduced, taking into account all the factors that can influence in the development of a CBM project. Then CBM resources have been quantified for Guardo-Barruelo basin accurately for every coal bed. After that, technical feasibility has been used to evaluate total amount of gas that can be recovered.

Research on management of coal bed methane warehousing and transportation based on GIS

At present Coal Bed Methane （CBM） has become the important part of clean energy in China. and will optimize the energy structure in China unceasingly. However, warehousing and transportation of CBM become one of the core factors that restrain its exploitation and utilization at present, due to the space-time character of natural deposit and modem utilization of CBM. In this paper, according to the character of CBM and the expanding trend of its utilization, the necessity of constructing the CBM＇s warehousing and transportation management system demonstrated. Index system that influence CBM＇s warehousing and transportation is established. And CBM＇s warehousing and transportation model is established by Voronoi diagram. In light of above research, CBM＇s warehousing and transportation management system based on Geography Information System （GIS） is designed, Using this system, CBM＇s warehousing and allocation center in one mining area is optimized. Research shows that to reinforce CBM＇s warehousing and transportation management is one of the key factors for coordinating the development of its development and utilization, thereby ensuring its sustainable development and utilization.

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

A critical review on direct catalytic hydrogasification of coal into CH_(4):catalysis process configurations,evaluations,and prospects

Coal catalytic hydrogasification(CCHG)is a straightforward approach for producing CH_(4),which shows advantages over the mature coal-to-CH_(4) technologies from the perspectives of CH_(4) yield,thermal efficiency,and CO_(2) emission.The core of CCHG is to make carbon in coal convert into CH_(4) efficiently with a catalyst.In the past decades,intensive research has been devoted to catalytic hydrogasification of model carbon(pitch coke,activated carbon,coal char).However,the chemical process of CCHG is still not well understood because the coal structure is more complicated,and CCHG is a combination of coal catalytic hydropyrolysis and coal char catalytic hydrogasification.This review seeks to shed light on the catalytic process of raw coal during CCHG.The configuration of suitable catalysts,operating conditions,and feedstocks for tailoring CH_(4) formation were identified,and the underlying mechanisms were elucidated.Based on these results,the CCHG process was evaluated,emphasizing pollutant emissions,energy efficiency,and reactor design.Furthermore,the opportunities and strategic approaches for CCHG under the restraint of carbon neutrality were highlighted by considering the penetration of“green”H2,biomass,and CO_(2) into CCHG.Preliminary investigations from our laboratories demonstrated that the integrated CCHG and biomass/CO_(2) hydrogenation process could perform as an emerging pathway for boosting CH_(4) production by consuming fewer fossil fuels,fulfilling the context of green manufacturing.This work not only provides systematic knowledge of CCHG but also helps to guide the efficient hydrogenation of other carbonaceous resources such as biomass,CO_(2),and coal-derived wastes.

高温和高压下CBM的爆炸极限

利用自主开发的实验装置,测定了20,60,100,150,200℃及常压,100,200和300 kPa初始条件下煤层气(CBM)的爆炸极限值.结果表明,随初始温度和压力的增加,爆炸极限上限变大,下限变小,爆炸极限范围变大,危险性增加;初始温度和压力对爆炸极限上限的影响大于对爆炸极限下限的影响.研究结论为CBM开发使用过程安全工艺参数的确定提供了实验依据.

CO_2—ECBM地质空间数据库建设方法研究

针对CO2-ECBM煤层气开发技术实施面临多源、多尺度、多类型数据管理与分析问题,基于GIS提出了一种CO2-ECBM地质空间数据库建设方法。首先按照需求通过区域与矿井地质调查、钻孔工业测试分析等方式获取数据,然后对获取的数据进行细化、空间参考共享和分类编码,最后按照Geodatabase数据模型存储数据,从而实现了数据的共享、管理及可视化和应用分析,为CO2-ECBM技术实施提供了决策支持。