Influence of liquid water on coalbed methane adsorption: An experimental research on coal reservoirs

ARTICLESChinese Science Bulletin 2005 Vol 50 Supp. 79-85Gases consist mainly of methane, as well as a little gaseInfluence of liquid water onous water, carbon dioxide, nitrogen, other weighty hydro-carbon gases, etc. Main liquids are liquid water, some-coalbed methane adsorption: times ontaining some liqud hydrocarbon Coal matrixAn experimental research onresentations of interaction of gas and solid, while macro-pores from coal matrix provide a vacuum for gas migracoal reservoirs in the south of tion and storage. Gas-liquid interaction mainly indicatesgas dissolution and escape from water. Solid-liquid interQinshui Basinaction mainly includes that wetting of coal matrix surface,filling and migration of water in pores. Solid-gas,huxun ZHU Yanming, ZHANG Jing.gas-liquid and solid-liquid interactions usually occur con-Xiaodong ZHANG Shiyincurrently, and affect each other. There have been manyresearches on coalbed methane adsorption/desorption, andCollege of Resource and Earth Sciences, China Ursity of Mining and the relationships among adsorbing gas, free gas, and dis-Correspondence should be addressed to Sang Shuxun (email: solving gas, etc. related to the interactions of solid-liquidand gas-liquid by predecessors 2 as well as by the auAbstract Using Isothermal Adsorption/Desorption Sys. thors 13-17 But there are few attentions on gas adsorptiontem Model IS-100 and Electrohydraulic Servo Rock System influenced by solid-liquid interaction, which is the topic ofModel MTS815 as the main apparatuses and collecting sam. the paper based on the experimentsples from the major coal reservoirs in the south of Qinshui Former researches figure that gaseous water has re-Basin, a hot point region of coalbed methane exploration, the markable influence on coal adsorbing gases, that is, thepaper carries out systematical comparisons of the isothermal adsorbability of coal shrinks along with the increase ofadsorption experimental data for injection water coal sam- gaseous water in coal 8, 9, because water molecule hasrium moisture samples and dry coal samplespolarity, and coal adsorbs water molecule preferentiallyprobes and establishes an experimental method of injection which will change the adsorption potential and energy ofsimulate real reservoir conditions, and then summaries the coal. But if water content exceeds the critical water con-experimental regulations and discusses the mechanism of tent( the equilibrium moisture), namely, gaseous waterliquid water influencing coal methane adsorption. Results of reaches the relative saturation and liquid water appears,the experiment indicate that: The Langmuir volume of injec- water content will no longer influence the adsorbability oftion water coal samples is notably larger than that of equilib- coal, I9In another word, liquid water has no effect onrium moisture samples, as well as larger than or equivalent the adsorbability of coal. The predecessors'comprehento that of dry coal samples; the Langmuir pressure of injec- sion is based on gas absorption experiment in certain contion water coal samples is the highest, the next is equilibrium ditions, which mainly indicates that water content of coalwhich the experimental results of injection water samples to samples tested was usually got by means of dry coal sam-simulate real reservoir conditions are more close to the fact. ples adsorbing gaseous water or immerging in liquid waterUnder the conditions of in-position reservoirs, liquid water in at normal temperature and pressure. Then, because of porecoals has evident influence on methane adsorption ability of interface intension, liquid water can only wet the outsidecoal matrix, which can increase the adsorbability of coal and surface of coal and some macropores(seeping pores)thatmake the adsorption regulation fit to Langmuir model better. have few effects on adsorbability of coal. Further, liquidIts major reason is the increase of wetting coal matrix ad- water cannot overcome surface tension to get into the agsorbability. The above experimental results overthrow the glomeration-adsorption pores and the adsorption poresconventional cognition that liquid water has no influence on with small aperture. So liquid water has no apparent in-coalbed methane adsortion,which may lead to an im- fluence on the adsorbability of coalprovement of the coalbed methane isothermal adsorptionexperimental method and of the reliability of coalbedAn important fact that we should pay more attention tomethane resource evaluation and predictionis that the experiment condition the predecessors'conclusion depends on is different from the true stratigraphicKeywords: coal reservoir, liquid water, methane adsorption, influ- circumstance of coal reservoirs, where liquid water pres-sure might reach 8 MPa, and temperature might reachDOI:10.1360/98zk001245C at 1000 m buried depth in a region with nortemperature and pressure gradients. Compared withUnder the in-position stratigraphic conditions, the coalnor中国煤化工: condition,, under thereservoir is a solid-liquid-gas coupling system. Solid coal stratiCNMHcanmatrix is a microporous, complex multiporous medium overdinto pores with smallthat is mainly composed of organic macromoleculesaperture. will the liquid water get into the coal's adsorpChinese Science Bulletin Vol 50 Supp. December 2005ARTICLEStion pores and make a notable effect on the adsorbability 1. 2 Water injection experiment of the coal samplesof coal? Is the influence of the regularity? what is the() Basic principle. Inner surface wetting and infillingmechanism of the wetting phase acting the adsorption of coal matrix pores are restricted by po in entering pophase on the inner surface of coal? This paper will discussand try to reply the above questions basing on isothermalterface strain. If liquid water succeedof the coal matrix and wets the inner surface of coal maadsorption experiments under the stimulated stratigraphic trix pore, it must first conquer the influence of solid-liquidinterface strain. The smaller the pores' aperture is, the1 Experimental methodsgreater the influence is, and more hard the liquid waterenters. Capillary additional pressure of the agglomeration1. 1 Sample selection and preparationadsorption pore and the adsorption pore is not enough toQinshui Basin, a region with the highest degree of make water enter the pores. Only if extra pressure is bigenoucoalbed methane exploration and exploitation, may hopgh, liquid water can conquer solid-liquid interfacestrain, enter into the agglomeration-adsorption pores andfully get an industrial outburst in the country, which is the adsorption pores and wet their inner surface. The big-Fundamental Research and Development Program, Ba- ger the water's pressure is, the smaller the aperture of thealso the major region of interest of the National Keysic Researches on Pool-forming Mechanism and Eco- When the water pressure is removed, as liquid water cannomic Exploitation of Coalbed Methane in China. 20 rep- not be compressed, the water in the coal matrix poresresentative coal samples, weighing 370 kg in total, are cannot conquer the solid-liquid interface strain to effusepicked to be tested from Yangquan, Heshun, Lu' an, and then injection coal samples can be gotJincheng, Yangcheng, Qinyuan in Qinshui basin. In order(ii) Granularity choice of the experimental sampto do comparative experiments under different conditions The work's purpose is to research the effect of liquidfor each coal sample, the sample should satisfy require- ter infilling coal pores and wetting their inner surface onments as follows: To be more representative, macrolitho- the features of coal adsorbing methane. In order to elimitypes of coal are relatively homological and ordinary to nate interference of wetting water on coal grain outer sur-prevent diversities which originate from differences of the face side of the samples and to maintain true pore struclithotypes of coal in the process of crashing and splitting, ture, theoretically, the bigger the sample 's granularity is,is split to 8 parts, and each part weighs more than 700 g, the better its representativity is. But in practice, theso the mass in sum is more than 6 kg. Among the 20 sam- granularity of coal grains can have apparent influence onples, the sample of No. 3 coal seam of Chengzhuang mirequilibrium time of coal adsorbing methane andJincheng is chosen as the test sample, characterized by the injection effects of coal samples, in detail, the experimenfollowings:The main macrolithotype of coal is clarain, tal period will greatly delay with the increase of samplecontaining some vitrain linears, apart from a strip ofgranularity. Fig. I shows that for dry coal sample isother-durain being eliminated, no fusain; vitrinite is 86%,inertinite 9%, exinite 1%, mineral 4%; the maximum reflec- mal experiments, the period of granularity of 5-10 mm isance of vitrinite is 3moisture is 3.3%, ash 6.72.7 times longer than that of granularity of 0. 1-0.3 mm;volatile vield 6.6%. and fixed carbon 83.4% of air water for equilibrium moisture sample isothermal experiments,the period of 5-10 mm is 3.3 times longer than that ofCrash 6.5 kg test sample into centimeter grains; then 0. 1-0.3 mm Granularity has much influence on the timeplit the crashed sample into 8 parts, of which one part of water injcction equilibrium, that is, the effect of waternamed CZ8 is taken as the spare, and the other 7 parts are injection will get worse along with the increase of grantrespectively crashed into 10.0-5.0 mm(CZ1), 5.0-2.0mm(CZ2,2.0-1.0mm(CZ3),1.0-0.5mm(CZ4),0.50.3 mm(CZ5), 0.3-0 1 mm(CZ6), smaller than 0.1mm(CZT); further, respectively split CZI-CZ7 into 6hares, of which one share is prepared for a dry coal sam-ple, one share for an equilibrium moisture coal sample, the200HI-Dry coal sampleother 4 shares for injection water samples. For the dry coal asample, the coal will be dessicated in oven for 2 h at temE100eQuilibrium moisturecoal sampleerature of 105C, for the equilibrium moisture sample, n中国煤化工the coal will sorb gaseous water fully in a saturated mois-ture at 30C( detailed operation shown in ref [3D: for theC NMHGrity/mminjection water samples, the water injection experiment is Fig. 1. Effects of coal sampleity on period of isothermal ex-designed belowchinese Science Bulletin Vol 50 Supp. December 2005ARTICLESlarity Granularity of the experimental samples should not whose size is equivalent to the rock column samplebe excessively big. Anciently, sample granularity for iso-(v)Water injection at high pressure. Connect thethermal adsorption experiments is usually 60-80 mesh sample cell full of immerged coal samples and sample iso-(0.18-0.28 mm). Once those samples are used to inject lators with air-proof adhesive tape; then put them intoater,they will become coal slurry, which presentsairtight pressure capsule of the Electrohydraulic Servoparently to be too fine. But, are results of the experiments Rock System; inject water at high pressure from both sidescomparable between the former samples and the coarse of the sample cell. The experimental conditions followsamples? In order to evaluate the effects of sample's room temperature 25#3C, pressures 8 MPa, 12 MPa, 16granularity on experimental results, isothermal experi- MPa and 20 MPa, injection time 3 h under a stable pressure,ments of dry coal samples and equilibrium moisture sam- and the injected water is distilled water. After withdrawingples with different granularity are done and compared. The pressure and stopping water injection, take the sample cellresults show that dry coal sample granularity has no effect. out and weigh the cell when there is no water drops fromand equilibrium moisture sample granularity has few ef. the bottom hole; then send the coal sample for the iso.fects on Langmuir volume but notable effect on Langmuirthermal adsorption experiment within 10 min.pressure and the curve shape of isothermal adsorption ofFor experimental pressure, there are the following threeaspects to be considered: Firstly, the stratigraphic pressurelower pressure portion(Fig. 2). That sample granularity condition should be simulated within the evaluation depthhas no effect on Langmuir volume provides a foundationfor the comparability of experimental results when the ofof coalbed methane resource; secondly, water injectionpressure should be higher than gas injection pressure ofsample granularity increases. But in isotherm experiments, isothermal adsorption experiments to prevent pore distri-the effect of granularity on Langmuir pressure deserves bution of injection water from influence of gas injection;much attention. After summarizing all the analyses thirdly, water should be injected under different pressures,above,the granularities of 5-10 mm(CZI)and 2-5 mm in order to analyze liquid water effect on coal adsorbingCZ2)are chosen as the injection water samplesmethane under the conditions of different pressures and(i) Desiccation and vacuumpumping of coal samples. pore distributions. The experimental apparatus is the elec10 mm and 2-5 mm, CZI and CZ2 in an oven for 2 h at MTS Company in U.S.A.ystem Model MTS815 made bytemperature of 105C, and weigh them; then put the sam-ples in self-made sample tins respectively, seal the tins and 1.3 Isothermal adsorption experiments of the coal sam-attach the tins to a vacuum pump, vacuumize continuously plesfor 8 h at room temperature. Vacuum pump is Model ZX-2The experimental apparatus is Isothermal Adsorp-sliding vane rotary vacuum pump, with 2 litre per second tion/Desorption System Model IS-100 made by Tema Tekof pumping speed, 6x10 Pa of ultimate vacuityCompany in U.S.A., the experimental principles are the(iv) Water immersion at atmospheric pressure. Turn volume method, the single molecule layer adsorptionoff the valve connecting the vacuum pump and the sample model, and the Langmuir equation used to fit isothermaltin, remove the pump; dip the vacuumized tin into distilled adsorption curves and calculate related parameters. Exwater in a vessel; turn on the valve and let distilled water perimental conditions are: temperature 25 C; the maxiflow into the sample tin; immerge the sample for 15 h, and mum initial pressure 12 MPa of dry coal sample and equi-then remove the sample to a self-made sample cell; weigh librium moisture sample isothermal adsorption experithe cell when there is no water dripping from the hole at ments and 8-12 MPa of injection water sample isotherits bottom(the cell's dry weight and wet weight are given). mal adsorption experiments; methane purity of experi-The sample cell is made according to the specimen re- mental gas 99.99%. See ref [3 for detailed experimentalquirements of the Electrohydraulic Servo Rock System, principle and procedure35Dry coal sampleDry coal sample三1.0-C EquilibriummoistureDH- Equilibrium moisturecoal sample中国煤化工Sample granularity/mmCNMHGFig. 2. Effects of coal sample granularity on experimental results of the isothermal adsorption (a) Sample granularity and Langmuirvolume; ( b)sample granularity and Langmuir pressureChinese Science Bulletin Vol 50 Supp. December 2005ARTICLESTable 1 Experimental resultsEquilibrium moisture sampleb(%)(m/(MPa)(h)(MPa)(%)(m/)(MPa)(h)34,103.495-1031.210.3336154725001.8740297230.732644331613.0234893.8643012.13.1332461.5013.072-531.210.3833956829571844001613743569240340123030.751-231210.3228356229551054000531950.151506.2629490851840.3-0531.210.2514170430071.15160Cz601-03307701913556125390641222 Experimental resultsstratigraphic circumstance can increase the adsorbabilityof coal matrix and the theoretical maximum adsorptionThe experimental results of moisture equilibrium ex- and desorption rate coefficient becomes larger than ad-periments, water injecton experiments, isothermal ad- sorption rate coefficientsorption experiments for dry coal samples, equilibriumThe comparison of isothermal adsorption curves for in-moisture samples and injection water samples are shownjection water samples, equilibrium moisture samples andin Table I, where Vi represents Langmuir volume (m/t), dry coal samples(Fig. 4) is as follows: In the portion ofPL Langmuir pressure(MPa), TE adsorption time(h), WE low pressure(<5 MPa), the curves for the injection waterthe amount of equilibrium moisture (%), Pr coal samplesample and the equilibrium moisture sample are close, andwater injection pressure(MPa), Wi the amount of injection the adsorption amount of the injection water sample isThrough further analyses of the isothermal adsorptionexperiment results of Carboniferous-Permian main coalreservoirs in south Qinshui basin, the following knowledge can be got:By comparison of experimental data of the three kinds◆--二二of samples, Langmuir volume of the injection water sam-ple is apparently bigger than that of the equilibrium mois. 5 20:ture sample, and also bigger than or equivalent to that ofthe dry coal sample. Langmuir pressure of the injectionsample is the highest, the equilibrium moisture sample isthe next, and the dry coal sample is the lowest(Fig 3). Inanother word, the liquid water in coal reservoirs unde◆ Dry coal sampleMeasured points for the dry coal samplesa Equilibrium moistureFitted line for the dry coal samplescoal sampleMeasured points for the equilibrium moistureA Injection water coal sicoal samples24Fitted line for the equilibrium moisture coal samplesLangmuir pressure/MPa中国煤化工 ction water coal samplesFig. 3. Distribution and comparison of the isothermal adsorption paCNMHGwater coal samplesrameters of the dry, the equilibrium moisture and the injection water coal Fig. 4. Comparison of the isothermal adsorption curves of the dry, theequilibrium moisture and the injection watersamples( CZ-1)Chinese Science Bulletin Vol 50 Supp. December 2005ARTICLESapproximately equivalent to that of the equilibrium mois- inhabit the adsorption potentialsler surface of theture sample but notably smaller than that of the dry coal coal matrix, which causes the decrease of the adsorbabilitysample; in the portion of medium pressure(S-15 MPa), of the equilibrium moisture sample in respect of the drythe curves for the injection water sample and the equilib- samplrium moisture sample have apparent separation, and the coal pores, the liquid water conquers surface tension toadsorption amount of the injection water sample is bigger wet pore inner surface of the coal matrix and forms waterthan that of the equilibrium moisture sample but smaller film. There is strong Keeson force between coal moleculesthan that of the dry coal sample; in the portion of high and the first layer water molecules, which contributes topressure (15 MPa), the curve for the injection water form a continuous water molecule adsorption layer.Thesample gradually approaches to and finally surpasses that force between coal molecules and the second layer waterfor the dry coal sample, and the adsorption amount of the molecules becomes evidently feeble because of the actioninjection water sample is close to or more than that of the in a reverse direction of hydrogen bond between the firstdry coal sample along with the increase of pressure and layer molecules and the second layer molecules. Andapproaches to the final saturation adsorption; the dry coal forces between coal molecules and outside layer watersample approaches the maximum saturation adsorption molecules become weaker and weaker. Here, the adsorp-volume at pressure 6 MPa, the equilibrium moisture sam- tion potentials of the outer surface of the first waterple at pressure 10 MPa, while the injection water sample molecule layer can be inhabited by methane moleculesat pressure 30 MPa; degree of fitting between isothermal which dissolve and diffuse in liquid water, as methanedsorption curves and experimental data of the injection molecule has no polarity and the direction of the adsorpwater sample is the highest, the equilibrium moisture tion force between coal molecules and gas molecules issample is the next, and the dry coal sample is the worst.the same to that of the acting force between the first layerWhen pressure is above 8 MPa, the measured adsorp- water molecules and gas molecules. It can be found outtion volumes of all the 6 dry coal samples decrease, those that the adsorption force of coal matrix molecules withof three of the 6 equilibrium moisture samples decrease, wetting surface to methane molecules becomes muchbut no similar phenomena occur for the 8 injection water stronger, but the adsorption force of coal matrix moleculessamples (Table 1)to free water molecules decreases apart from the first layerLiquid water has notable influence on coal matrix ad- tied water molecules, so the competition adsorption forceof free water molecules becomes very weak, which induces that the gas adsorbability of the injection water3 Discussionsamples is better than that of the equilibrium moisture3.1 The mechanism of liquid water influencing gas ad- samples. Especially when gas pressure is high and gassorption of coal matrixsolubility and diffusion velocity notably increase, the superiority of the injection water samples adsorbing gases isBasic structural unit of the three-dimensional chemic more remarkable. Compared with the dry coal samples,cross-linking network model of coal macromolecules is the adsorbability of coal matrix of the injection wateraromatic nucleus; coal macromolecule's bridge bond and samples to gas molecules increases a little, while the adcross-linking bond are the second level of the network; a sorption potentials have no evident decrease, so the ad-arge amount of atomic groups around aromatic nucleuses sorbability (Langmuir volume)of the injection waterare the third level, among which some are acid and some samples is equivalent to or a little larger than that of theare alkaline. In coal,'s organic structures, there are con- dry coal samples. But when the gas pressure is lower, duetaminant atoms such as O, N, and S that form many func- to the influence of gas solubility and diffusion velocity intional groups. Many coal macromolecules'atomic groups water, gas adsorption volume of the dry coal samples isand functional groups have polarity 22. When gaseous bigger than that of the injection water samples.Thewater molecules, gas molecules of methane and others crease of adsorption force of wetting coal matrix is thecompete to be adsorbed on the surface of coal matrix, be- main cause to strengthen adsorbability of the injectioncause water molecule has polarity, the priority of Van der water coal sampleswaals force between coal molecule and water molecule isAccording to Sang Shuxun's research in 20045,6,ag-Keeson force. However, the structures of methane( CH4), glomeration-adsorption pores of the coal reservoirs in thenitrogen(N2)and carbon dioxide( CO2), main components south of Qinshui basin relatively develop. Along with gasof coalbed methane, are of spatial symmetry or linear pressure increasing and approaching to saturation steamsymmetry and have no polarity and inhere electric mo- pressure, under the action of capillary force, gas multiment, so the adsorption force between coal molecules and molecly London force and de中国煤化工 glomeration occur inr the isothermal Adforce. Keeson force is stronger than London force and sorptioCNMHG basic method to getDebye force. So gaseous water molecules are prone to adsorption volume is the gas amount injected in sampleChinese Science Bulletin Vol. 50 Supp. December 2005ARTICLEScells minus the free gas amount in sample cell free space bearing saturation calculated and critical desorption presneasured through the helium injection before injecting sure estimated are lower, production estimated is higher,adsorbed gases. When injecting gases under high pressure, production peak comes later, and recovery ratio of coalbedgases agglomerate in the agglomeration-adsorption pores, methane estimated is higher.so the true free space is smaller than that meast(ii)When the pressure of coal reservoirs is less than 5through the helium volume. The experimental system still MPa, the difference above-mentioned is not evident. Foruses helium to measure the free space and to calculate the the experimental samples, the isothermal adsorptionfree gas amount, so the calculated free gas amount is lar- curves of dry coal samples and equilibrium moisture samger than the fact, and the obtained adsorption amount is ples begin to separate from each other at 5 MPa. As tosmaller than the fact, which contributes to the phenome- other regions or coalbed samples, they might separate atnon that the adsorption volume of coal matrix decreases different pressure. Along with increase of gas pressure, thewith gas pressure increasing. When liquid water enters reality of isothermal adsorption experimental data andinto pores of coal matrix, liquid water conquers pore sur-. isotherm adsorption curves of equilibrium moisture sam-face tension and applies work, which makes the gas capil- ples becomes bad, which will bring discrepancy, evenlary surface tension effect decrease of coal matrix pores, false cognition to resource evaluation of coalbed methane.especially of agglomeration-adsorption pores.2. Thus, So isothermal adsorption experiments of injection waterthe gas agglomeration becomes weak greatly, which samples simulating the conditions of coalbed reservoirsrepresents that the experimental data fit the Langmuir are the essential approach to solve the problem.equation better, and the phenomenon disappears that theadsorption volume decreases with the pressure Increasing. 4 ConclusionsThe experimental method has influence on the results tooBy comparative researches on the isothermalGases dissolved in liquid water can result in the in- tion experiments of the injection water samples,crease of the adsorbability of the injection water samples. rium moisture samples and dry coal samples, the follow-But below the pressure of 20 MPa, the amount of wa- ing conclusions can be drawnter-dissolved gases does not exceed I m/t/4.. Evidently( )There are remarkable regulations and differencesliquid water dissolving gases is not the main cause to in- among isothermal adsorption experimental results of theduce the increase of the adsorbability of the injection wa- injection water samples simulating reservoir conditions,the equilibrium moisture samples and the dry coal samplesThe experimental result of the injection water samples is3.2 Research significance of effect of liquid water on more fit to the practical situation than that of the two othcoal matrix adsorbing gasesers. The isothermal adsorption experiment method of theCoal matrix adsorbing gases is one of the basic charac- injection water samples simulating reservoir conditionsteristics of coal reservoirs. According to the adsorp- will hopefully replace the current applied method of thetion/desorption features of coal reservoirs, gas content can equilibrium moisture sample isothermal adsorption exbe predicted, gas bearing saturation can be calculated, criti- perimentcal desorption pressure can be estimated, coal reservoir(ii)Under the conditions of coal reservoirs, liquid watersimulation and production forecast can be done, and the in coal seams has an evident effect on coal matrix adsorbrecovery ratio of coalbed gas can be evaluated. The iso- ing gases, which can make gas adsorbability of coal mathermal adsorption experimental results of injection water trix rise, and makedsorption regtulation answer forsamples indicate that liquid water has a notable effect on Langmuir model better.gas adsorption of coal matrix. Under simulating reservoir (ii) The increase of adsorption force of wetting coalconditions, they are more close to the practical situation matrix is the main cause to strengthen gas adsorbability ofthan dry coal samples and equilibrium moisture samples. the injection water samples. The weakening agglomeraThough Langmuir volumes of injection water samples and tion in the adsorption-agglomeration pores related to theequilibrium moisture samples are almost the same, the dif- liquid water in coal matrix pores, as well as the experiferences of isothermal adsorption curves and gas adsorption mental method, and also has an effect on the experimentvolumes between injection water samples and equilibrium results. However, dissolved gases in water have little inmoisture samples are much smaller under the pressure of fluence on the experimental resultsreservoirs within the evaluation depth of coalbed gas(2000(iv)The results of isothermal adsorption experimentsm). However, compared with equilibrium moisture samples, have notable influence on gas content prediction, gasexperimental results of isothervpcalculation. critical desorption pressuretion water samples also have influence on coalbed methane es中国煤化工n, production potentialresource evaluation and exploitation as follows(i )When the pressure of coal reservoirs is more than or CoallCNMHGOVery ratio evaluationve deviation basedequals to 5 MPa, gas content forecasted is higher, gas results of the isothermal adsorption experiments of equiChinese Science Bulletin Vol. 50 Supp. December 2005ARTICLESlibrium moisture samples12. Busch, A Gensterblum, Y, Krooss, B, Methane and COz sorptionAcknowledgements The authke to thank Shanxi Bureau ofand desorption measurements on dry Argonne premium coals: pureCoal Geology and Jincheng Mifor helps during the work ofsample collection. This workby the National Key Fundacomponents and mixtures, Int. J. of Coal Geol., 2003, 55, 205mental Research and Development Program( Grant No. 2002CB211703)References13. Sang, S, Qin, Y, Fan, B, Features of low rank coal reservoir in1. Zhang, X, Zhang, S, Zhong, L, Coalbed Methane in China (inlimnic basins. Journal of China University of Mining and TechnolChinese). Xi'an: Shanxi Science and Technology Press, 1991, 30ogy( in Chinese,2001,30(4):341-3414. Sang, s, Qin,2. Liu, C, Yang, S, Experimental research on adsorption regulationbed gas in Junggar and Tuha Basins, Geological Jourmal of Chinaof the coal adsorbing methane system, Safety in Coal Mines (inUniversities( in Chinese), 2003, 9(3): 365-372Chinese),1992,22(4):1-5.15. Sang, S, Zhu Y, Zhang, S, Solid-gas interaction mechanism of3. Qian, K, Zhao, J, Wang, Z, Coalbed Methane Exploration andcoal-adsorbed gas(I)-coal pore structure and solid-gas interaction.Development Theory and Experimental Testing Technology(inNatural Gas Industry (in Chinese), 2005, 25( 1): 13-15Chinese), Beijing: Petroleum Industry Press, 1996. 119-142.16. Sang, S, Zhu, Y, Zhang, J, Solid-gas interaction mechanism of4. Nie, B, Duan, S, The adsorption essence of gas on coal surface(incoal-adsorbed gas(In) -physical process and theoretical model ofChinese), Journal of Taiyuan University of Technology, 1998, 29(4)as Industry(in Chinese), 2005, 25(1)5. Zhang, Q, Yang, X, Isothermal adsorption of coals on methane17. Sang, S, Zhu, Y, Zhang, J, Coalbed methane storage and dynamicunder equilibrium moisture, Joumal of China Coal Society (inChinese,l999,24(6:566-570.equilibrium of the three states, Collection in Coalbed Methane6. Zhang, L, He, X, Wang, E. et al., Study of absorptive characteris-Pool-forming Mechanism and Theoretical Base of its Economicaltics of coal, Journal of Taiyuan University of Technology (in ChiExploitation(eds. Sang, Y, Zhang, x)(in Chinese), Beijing: Sci-nese),200l,32(5):449-451ence press. 2004. 90-98.7. Zhong, L. Adsorptive capacity of coals and its affecting factors, 18. Joubert, J, Grein, C, Bienstock, D, Sorption of methane in moistEarth Science-Journal of China University of Geosciences (incoal,Fuel,1973,52:181-185Chinese),2004,293):327-332.19. Joubert, J, Effect of moisture on the methane capacity of American8. Tang, s, Tang, D, Yang, Q, Binary-component gas adsorptionoals,Fuel,1974,53:186-191isotherm experiments and their significance to exploitation of 20. Zhu, L, Surface and Interface Physics(in Chinese), Tianjin: Tian-coalbed methane, Earth Science- Joumal of China University ofUniversity Press, 1992. 124-166Geosciences(in Chinese), 2004, 29(2): 219-22321. Yalcin, E, Durucan, S, Methane capacities of Zonguldak coals and9. Moffat, D, Weale, K, Sorption by coal of methane at high pressure,the factors affecting methane adsorption, Mining Science Tech-Fue,l955,34:449nology,1991,13(2:2l5-22210. Crosdale, P, Beamish, B, Alix, M, Coalbed mcthane sorption re- 22. Nie, B, He, x, Wang, E.et al., Micro-mechanism of coal adsorblated to coal composition, Int J. of Coal Geol., 1998, 35(1-4)ing water, Joumal of China University of Mining and Technologyin Chinese,2004,33(4):379-383I1.Clarkson, C,Bustin,R, Binary gas adsorption or desorption iso- 23. Gregg, S Sing, K Adsorption, Surface Area and Porosity, Londontherms: effect of moisture and coal composition upon carbon dioxde selectivity over methane, Int, J of Coal GeoL, 2000, 42: 241-Academic Press, 1982,(Received March 15, 2005; accepted July 6, 2005)中国煤化工CNMHGChinese Science Bulletin Vol 50 Supp. December 2005