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Thermodynamic Characteristics of Adsorption-Desorption of Methane in 3# Coal Seam of Sihe  [PDF]
Dongmin Ma, Jianchang Zhang, Jianping Bai, Hui Zhang
Natural Resources (NR) , 2014, DOI: 10.4236/nr.2014.512067
Abstract: A series of methane adsorption-desorption isotherm experiments on anthracite of No. 3 Sihe coal mine were conducted at 20°C, 25°C, 30°C, 35°C and 40°C respectively. Based on Clausius-Clapeyron equation, isosteric heat of adsorption and maximum heat of adsorption has been calculated. These calculations indicate that the maximum heat of adsorption in process of elevated pressure (adsorption) and lowered stress (desorption) is 23.31 KJ/mol and 24.02 KJ/mol, so it belongs to physical adsorption. However, the latter is higher than the former. From the point of view of thermodynamics, in the adsorption-desorption equilibrium system, dropping pressure alone does not lead to desorption, but it improves adsorption of water vapor molecules on the surface of the coal pores. The adsorption heat of water vapor molecules is greater than 40 KJ/mol, so the methane on the surface of coal pores will be easily replaced by water vapor, and the desorption of methane occurs eventually. Thus, the gas production in coalbed methane well by pressure reduction is consistent with the negative pressure for gas extraction.
A Critical Review of Methane Trapping Mechanism to Optimize CBM Production  [cached]
Saleem Qadir Tunio,Swapan Kumar Bhattacharya,Sonny Irawan
Research Journal of Applied Sciences, Engineering and Technology , 2012,
Abstract: Optimizing Coal Bed Methane (CBM) production depends on the trapping mechanism of methane in the micro pores of coal bed. Methane is trapped in coal beds by adsorption on the free surface. The free surface is mainly available as the micro pores and partly as different cleats. The average percentage of micro pores (1.2x10-7 cm diameter) in a coal increases with rank and ranges from 19.3% in lignites to 75% in anthracites. The effective molecular diameter of adsorbed methane is 4.1x10-8 cm suggesting a maximum of three molecules can be accommodated in a unit micro pore. The commitment of optimized production of methane depends on the amount adsorbed on the coal surface. Methane in the micro pore can be accommodated either by solution in pore water or adsorption or as free gas under pressure. If it is dissolved in water, then for CBM production it is not useful because the dissolved gas will be expelled during dewatering phase of the well completion. It is only the free gas and the adsorbed gas that need to be evaluated for optimized production. Langmuir assumed a mono-layer of adsorption in selective locales on the adsorbent whereas many of the present day models assumed multi-layers of adsorbates (BET: Stephen Brunauer, Paul Emmett and Edward Teller). Problem arises with the concept of layering during adsorption process whereby it is difficult to think of adsorption of methane over a methane layer. With higher pressure methane can be accommodated as free gas but will not be adsorbed on any methane surface. It is therefore necessary to understand how methane molecule is trapped in the micro pores of the coal bed in order to optimize the CBM production.
EXPERIMENTAL STUDY OF COALBEDS METHANE REPLACEMENT BY CARBON DIOXIDE
CO_2驱替煤层CH_4试验研究

LIANG Weiguo,WU Di,ZHAO Yangsheng,
梁卫国
,吴迪,赵阳升

岩石力学与工程学报 , 2010,
Abstract: Carbon dioxide is one of the main greenhouse gases. Geological disposal of carbon dioxide in coalbeds is regarded as an economical approach because of the mutual benefit of greenhouse gas sequestration and recovery of coalbed methane by replacement. In the past,most of works were focused on either theoretical analyses and numerical simulations,or experiments of adsorption and desorption of different gases on coal grains in size of millimeters or the less. In this paper,the experimental study results of carbon dioxide storage and methane replacement in coal specimens of large size(100 mm×100 mm×200 mm) are presented,which realistically simulates the process of the greenhouse gas sequestration and methane replacement in coalbed. In the experiment,the permeability of coal specimen is measured firstly with methane and carbon dioxide respectively;and it is found that the permeability of coal is different for the two gases. The permeability for carbon dioxide is larger than that for methane two magnitudes at least under the testing condition. There exists a negative exponent relationship between the permeability and applied body stress on the specimen. Under the simulated stress condition in the experiment,17.47 to 28.00 units of carbon dioxide can be stored in per unit of coal;and the replacement ratio of carbon dioxide to methane is as large as 7.03 to 13.91. The processes of injection,adsorption and desorption,replacement,and output of gases can proceed smoothly under the given pressures;the percentage of methane in the production gas can be amounted to 20% to 50% at the early stage and still can be maintained at the level of 10% to 16% even at the last stage during the experiment process. It is concluded that the effects of carbon dioxide storage and methane replacement are determined by several factors including injection replacement pressure,injection amount and velocity,methane content in the coalbed,and the development of pores and fissures in the coalbed,etc.. During the process of carbon dioxide injection and gas replacement,coal body swelling can be found with comprehensive effects of gas adsorption and desorption,and the deformation of coal framework. The research is expected to provide certain illuminations for practice of carbon dioxide disposal in coalbed or methane replacement recovery by carbon dioxide in the future.
Analysis of pore system model and physical property of coal reservoir in the Qinshui Basin
Hao Xu,Shanghu Zhang,Xue Leng,Dazhen Tang,Mingshou Wang
Chinese Science Bulletin , 2005, DOI: 10.1007/BF03184083
Abstract: The Qinshui Basin in China is a major area for exploration and development of high rank coalbed methane. Due to the high rank coal and complicated pore system, no substantial breakthrough in the exploration and development of coalbed methane has been made until now. Many systematic tests show that a pore system of coal reservoir has some features as follows: the porosity is relatively low; the pore system is dominated by micropores and transition pores; mesopores take the second place, and macropores are nearly absent, which is exceedingly adverse for production of coalbed methane. However, testing data also revealed the differential development for the pore of high rank coal reservoirs in the Qinshui Basin, which necessarily led to the different physical properties of desorption, diffusion and permeability. This paper classifies the testing data using cluster analysis method and selects the typical samples to establish four pore system models, analyzes the differences of reservoir physical property, and provides a guidance for the exploration and development of coalbed methane in the Qinshui Basin.
Displacement desorption test of coalbed methane and its mechanism exploring
Suian Zhang,Yongzhong Huo,Jianping Ye,Shuheng Tang,Dongmin Ma
Chinese Science Bulletin , 2005, DOI: 10.1007/BF03184100
Abstract: Through the test of CH4 displaced by CO2 using the coal sample as the adsorbent, this paper has found the coalbed methane (CBM) displacement desorption phenomenon under the natural conditions and CBM mining conditions. With the help of the adsorption theory of the modern physical chemistry and interfacial chemistry, the CBM competitive adsorption and displacement desorption mechanism are intensively discussed, and a new path for studying the CBM desorption mechanism in the CBM exploitation process is explored.
THE INFLUENCE OF COAL FORMATION MACERAL TO NATURAL GASES CARBONISOTOPIC COMPOSITION AND ITS APPLICATION
煤系源岩显微组分对天然气碳同位素组成影响的应用

ZHANG Dian-wei,LIU Wen-hui,Liu Quan-you,Gao Bo,
张殿伟[]
,刘文汇[],刘全有[],高波[]

天然气地球科学 , 2005,
Abstract: Based on the analysis of desorption velocity and the capable desorption quantity of coalbed methane, we systemically discussed the desorption characteristics of coalbed methane of Panzhuang Coal mine and analyze the relationship between desorption velocity and desorption time , and the relationship between the capable desorption quantity and the burial depth of coal reservoir. In the area, there is quite high capable desorption rate in the middle area of the first mine field, most area of the fifth coal of the second mine field and the north area of the third coal of Panzhuang Coal mine, which is propitious to the exploitation of coalbed methane. In the layer region, the capable desorption rate mostly takes On a negative relationship with the increase of burial depth of coal reservoir, but the data is comparatively discrete.
Fractal classification and natural classification of coal pore structure based on migration of coal bed methane
Xuehai Fu,Yong Qin,Wanhong Zhang,Chongtao Wei,Rongfu Zhou
Chinese Science Bulletin , 2005, DOI: 10.1007/BF03184085
Abstract: According to the data of 146 coal samples measured by mercury penetration, coal pores are classified into two levels of <65 nm diffusion pore and >65 nm seeping pore by fractal method based on the characteristics of diffusion, seepage of coal bed methane(CBM) and on the research results of specific pore volume and pore structure. The diffusion pores are further divided into three categories: <8 nm micropore, 8–20 nm transitional pore, and 20–65 nm minipore based on the relationship between increment of specific surface area and diameter of pores, while seepage pores are further divided into three categories: 65–325 nm mesopore, 325–1000 nm transitional pore, and >1000 nm macropore based on the abrupt change in the increment of specific pore volume.
超声处理对煤层气解吸效果的影响
On the Effect of Ultrasonic Stimulation on the Desorption of Coalbed Methane
 [PDF]

孙仁远,纪云开,林李,胡爱梅,吴仕贵,陈东
- , 2015, DOI: 10.7520/1001-4888-14-056
Abstract: 煤岩吸附解吸性能评价对煤层气的开发十分重要。利用自行设计的煤岩吸附解吸性能评价装置,进行了CH4、CO2、N2等在煤岩中的吸附解吸性能评价。在此基础上,研究了不同参数超声波处理对煤层气解吸效果的影响,分析了超声波促进煤层气解吸的机理。研究表明,煤岩中的气体主要以吸附态和自由态存在,煤岩对不同气体吸附量从大到小依次为CO2、CH4、N2。经超声波处理后,煤层气的解吸速度可提高70%,同时煤层气的解吸量增加。解吸量增加幅度与超声波处理参数有关,随处理功率的增大,解吸量增加,增加幅度可达20%。分析认为超声波的“剥离”作用是超声波提高煤层气解吸效果的机理之一。
Coal adsorption and desorption performance evaluation is very important for the development of coalbed methane. A new device for coal adsorption and desorption performance evaluation was designed, based on which, performance evaluation of different gases, such as CH4, CO2 and N2 was carried out. On this basis, the effect of ultrasonic stimulation parameters on desorption of coalbed methane was studied, and desorption mechanism of ultrasonic stimulation was analyzed. Results show that the gases in coal and rock present mainly in both adsorbed and free states, the adsorption capacity for different coal gases is different, its descending order is CO2, CH4, N2. Compared with conventional desorption process, through ultrasonic treatment, the desorption rate of coalbed methane can be increased up to 70% and the desorption volume increases about 20%.The increase of desorption due to ultrasonic stimulation is related to the ultrasonic parameters. Higher the ultrasonic power is, the greater the desorption volume. The “Peel” effect of ultrasound is one of the mechanism of improvement of coalbed methane desorption
Influence of liquid water on coalbed methane adsorption: An experimental research on coal reservoirs in the south of Qinshui Basin
Shuxun Sang,Yanming Zhu,Jing Zhang,Xiaodong Zhang,Shiyin Zhang
Chinese Science Bulletin , 2005, DOI: 10.1007/BF03184087
Abstract: Using Isothermal Adsorption/Desorption System Model IS-100 and Electrohydraulic Servo Rock System Model MTS815 as the main apparatuses and collecting samples from the major coal reservoirs in the south of Qinshui Basin, a hot point region of coalbed methane exploration, the paper carries out systematical comparisons of the isothermal adsorption experimental data for injection water coal samples, equilibrium moisture samples and dry coal samples, probes and establishes an experimental method of injection water coal sample preparation and isothermal experiment to simulate real reservoir conditions, and then summaries the experimental regulations and discusses the mechanism of liquid water influencing coal methane adsorption. Results of the experiment indicate that: The Langmuir volume of injection water coal samples is notably larger than that of equilibrium moisture samples, as well as larger than or equivalent to that of dry coal samples; the Langmuir pressure of injection water coal samples is the highest, the next is equilibrium moisture samples, while the dry samples is the lowest, of which the experimental results of injection water samples to simulate real reservoir conditions are more close to the fact. Under the conditions of in-position reservoirs, liquid water in coals has evident influence on methane adsorption ability of coal matrix, which can increase the adsorbability of coal and make the adsorption regulation fit to Langmuir model better. Its major reason is the increase of wetting coal matrix adsorbability. The above experimental results overthrow the conventional cognition that liquid water has no influence on coalbed methane adsorption, which may lead to an improvement of the coalbed methane isothermal adsorption experimental method and of the reliability of coalbed methane resource evaluation and prediction.
ASSESSMENT OF ISTRIAN COAL BED METHANE PRODUCTION POSSIBILITY
Mario Klanfar,Domagoj Vulin,?elimir Veinovi?
Rudarsko-Geolo?ko-Naftni Zbornik , 2010,
Abstract: The potential of coal bed methane has not been evaluated in Croatia so far. For several selected sites in Labin basin data on the composition of coal and the depths and thicknesses of coal layers were collected. Assessment and comparison of the methane content in coal by using the Langmuir isotherm, the general curves of sorption and Kim's method was made and evaluation of the quality of each assessment as well. The analysis resulted with coal bed methane content between 9.5m3/t 11.73m3/t calculated by Kim's equation. By comparing the sorption of pure methane and sorption of CO2, in order to maintain the pressure in a coal bed and higher recovery of methane, the CO2 could be one of the options for injecting fluid. Geometry of coal layers was not defined and therefore it is not possible to estimate the total content of methane.
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