1、Designation: D7569 10Standard Practice forDetermination of Gas Content of CoalDirect DesorptionMethod1This standard is issued under the fixed designation D7569; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes methods for the direct determi-nation of the gas content of coal by desorption using samplesobtained by
3、drill coring methods from the surface. It sets outguidelines for the equipment construction, sample preparationand testing procedure, and method of calculation.1.2 Indirect methods for the determination of the gas con-tent of coal (not covered in this practice) are based on either thegas absorption
4、characteristics of coal under a given pressureand temperature condition or other empirical data that relatethe gas content of coal to such other parameters as coal rank,depth of cover, or gas emission rate.1.3 This practice covers the following two direct methods,which vary only in the time allowed
5、for the gas to desorb fromthe core, or sidewall core, before final crushing:1.3.1 The slow desorption method in which volumetricreadings of gas content are taken frequently (for example,every 10 to 15 min) during the first few hours, followed byhourly measurements for several hours, and then measure
6、-ments on 24-h intervals until no or very little gas is beingdesorbed for an extended period of time.1.3.2 The fast desorption method in which after initialdesorbed gas measurements to obtain data for lost gas calcu-lations, the canister is opened and the sample is transferred tothe coal crusher. Th
7、e remaining gas volume is measured on acrushed sample.1.4 This practice is confined to the direct method using core,or sidewall core obtained from drilling. The practice can beapplied to drill cuttings samples; however, the use of cuttingsis not recommended because the results may be misleading anda
8、re difficult to compare to the results obtained from coredesorption. The interpretation of the results does not fall withinthe scope of the practice.1.5 UnitsThe values stated in either SI units or inch-pound units are to be regarded separately as the standard. Thevalues stated in each system may no
9、t be exact equivalents;therefore, each system shall be used independently of the other.Combining values from the two systems may result in noncon-formance with the standard.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibili
10、ty of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D121 Terminology of Coal and CokeD167 Test Method for Apparent and True Specific Gravityand Porosit
11、y of Lump CokeD1412 Test Method for Equilibrium Moisture of Coal at 96to 97 Percent Relative Humidity and 30CD2799 Test Method for Microscopical Determination of theMaceral Composition of CoalD3172 Practice for Proximate Analysis of Coal and CokeD3173 Test Method for Moisture in the Analysis Sample
12、ofCoal and CokeD3174 Test Method for Ash in the Analysis Sample of Coaland Coke from CoalD3176 Practice for Ultimate Analysis of Coal and CokeD3180 Practice for Calculating Coal and Coke Analysesfrom As-Determined to Different BasesD3302 Test Method for Total Moisture in CoalD5192 Practice for Colle
13、ction of Coal Samples from CoreE1272 Specification for Laboratory Glass Graduated Cylin-ders2.2 Australian Standard:AS 3980 Guide to the determination of gas content ofcoalDirect desorption method31This practice is under the jurisdiction of ASTM Committee D05 on Coal andCoke and is the direct respon
14、sibility of Subcommittee D05.21 on Methods ofAnalysis.Current edition approved Sept. 1, 2010. Published October 2010. DOI: 10.1520/D756910.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
15、 information, refer to the standards Document Summary page onthe ASTM website.3Available from Standards Australia Limited, 286 Sussex St., Sydney, NSW,2000, Australia, GPO Box 476, Sydney, NSW, 2001 Australia or via the website:www.standards.org.au.1Copyright ASTM International, 100 Barr Harbor Driv
16、e, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.3 ISO Standard:ISO 6706 Plastics laboratory wareGraduated measuringcylinders42.4 DIN Standard:DIN 12681 Plastics laboratory wareGraduated measuringcylinders53. Terminology3.1 DefinitionsFor additional definitions of terms used inthis
17、practice, refer to Terminology D121.3.1.1 absolute permeability, npermeability of a rock to aparticular fluid when the rock is 100 % saturated with theflowing fluid. (1)63.1.2 absorbed gas, ngas that is molecularly dissolvedwithin a liquid phase or has penetrated into the lattice structureof a solid
18、. (1)3.1.3 actual lost gas time, nlost gas time determined fromthe time at which the sample being recovered reaches a depthwhere the hydrostatic pressure of the drilling fluid columnequals the original (immediately before sampling) reservoirpressure in the sample to the time at which the sample is s
19、ealedin a desorption canister.3.1.3.1 DiscussionEssentially, the actual lost gas time isthe amount of time between when the core starts its trip to thesurface and it is sealed in the canister. (1)3.1.4 adsorption, nattachment, through physical orchemical bonding, of fluid phase molecules to an inter
20、facialsurface.3.1.4.1 DiscussionThe adsorbed phase molecules are se-questered at the interfacial surface in a metastable equilibriumstate, the stability of which is strongly affected by changes intemperature and pressure. (1)3.1.5 adsorption isotherm, nquantitative relationship, atconstant temperatu
21、re, describing how the concentration ofadsorbed phase molecules at an interfacial surface varies as afunction of increasing system pressure. (1)3.1.6 as-received basis, nanalytical data calculated to themoisture condition of the sample as it arrived at the laboratoryand before any processing or cond
22、itioning.3.1.6.1 DiscussionIf the sample has been maintained in asealed state so that there has been no gain or loss, theas-received basis is equivalent to the moisture basis assampled. (D3180, D5192, D1412, D3302)3.1.7 canister, ncontainer that can be sealed into which acoal sample is placed to all
23、ow desorption to occur.3.1.7.1 DiscussionThe reduction in pressure to atmo-spheric pressure (at surface) causes the sample to release gasinto the canister. By measuring the amount of gas released andthe weight of the sample, the gas content can be determined.Gas content is conventionally reported in
24、 units of cubiccentimetres/gram (cm3/g), cubic metres/tonne (m3/ton), orstandard cubic feet/ton (scf/ton). (1)3.1.8 continuous coring, vrefers to continuous coringwith wireline recovery. (1)3.1.9 conventional core, n“large” diameter core (8.9 cmor 3.5 in. diameter or larger) in which the core barrel
25、 isrecovered to the surface after drilling a fixed interval by pullingthe drill string. (1)3.1.10 core, nin drilling, a cylindrical section of rock(coal) that is usually 5 to 10 cm in diameter taken as part of theinterval penetrated by a core bit and brought to the surface forgeologic examination, r
26、epresentative sampling, and laboratoryanalyses. (D121, D5192)3.1.11 cuttings, nin drilling, rock fragments that breakaway because of the action of the drill bit and are transportedto the surface by the drilling circulation system (mud or air).3.1.11.1 DiscussionCuttings may be screened and col-lecte
27、d from the circulation medium for lithologic characteriza-tion or analytical tests. (2)3.1.12 delivery tube, nflexible tube connecting a desorp-tion canister to a volumetric displacement apparatus. (1)3.1.13 desorption, ndetachment of adsorbed moleculesfrom an interfacial surface (see adsorption). (
28、1)3.1.14 desorption data analysis software, nsoftware usedfor analyzing desorption data. (1)3.1.15 desorption rate, nvolumetric rate at which gasdesorbs from a sample. (1)3.1.16 diffusion, nprocess whereby particles of liquids orgases move from a region of higher to lower concentrationindependent of
29、 the pressure gradient. (1)3.1.17 diffusivity, nratio of the diffusion coefficient to thesquare of a typical diffusion distance. (1)3.1.18 direct desorption method, nmethod for represent-ing desorption of gas from coal or other materials in which gasstorage as a result of adsorption is significant.3
30、.1.18.1 DiscussionIt mathematically presumes constanttemperature diffusion from a sphere initially at uniform gasconcentration. The solution of the basic equation adoptedsuggests that the measured desorbed gas volume is propor-tional to the square root of time since the start of desorption(time zero
31、). The direct method is the most widely used methodfor estimating lost gas volume. (1)3.1.19 dry, ash-free basis, ndata calculated to a theoreti-cal base of no moisture or ash associated with the sample.3.1.19.1 DiscussionNumerical values as established byTest Methods D3173 and D3174 are used for co
32、nverting theas-determined data to a moisture- and ash-free basis.(D3180)3.1.20 fast desorption method, nafter initial measure-ments to obtain the basis for lost gas calculations, the canisteris opened and the sample is transferred to a coal-crushingdevice that is modified so that the remaining desor
33、bed gasvolume from the crushed coal sample can be measured.(AS 3980)3.1.21 free gas, nunabsorbed gas within the pores andnatural fractures. (1)3.1.22 gas-in-place, namount of gas present in a seam oran interval of discrete thickness or in multiple seams or4Available from the International Organizati
34、on for Standardization (ISO), 1, ruede Varemb, Case Postale 56, CH-1211 Geneva 20, Switzerland or via the website:http:/www.iso.org/.5Available from Deutsches Institut fr Normung e. V., 10772 Berlin or via thewebsite: http:/www2.din.de.6The boldface numbers in parentheses refer to the list of refere
35、nces at the end ofthis standard.D7569 102intervals determined from the gas content, bulk density, thick-ness, and drainage area.3.1.22.1 DiscussionEstimates of gas-in-place usually re-flect total gas content, which in addition to methane, mayinclude others gases such as carbon dioxide or nitrogen. (
36、1)3.1.23 gas saturated, advstate in which the gas content(determined from direct or indirect desorption measurements)is equal to the gas storage capacity (determined from iso-therms). (1)3.1.24 gas storage capacity, nmaximum amount of gas orgas mixtures (normalized according to the relevant basis) t
37、hatcan be held by a sample at various reservoir pressures,reservoir temperature, and a specific moisture (water) content.(1)3.1.25 head space volume, nvoid space in a canistercontaining a sample.3.1.25.1 DiscussionCanister desorption measurementsare corrected for the effect of expansion or contracti
38、on of gasesin the canister head space in response to temperature andpressure fluctuations. (1)3.1.26 indirect method for the determination of the gascontent of coal, nmethod based on either the gas absorptioncharacteristics of coal under a given pressure and temperaturecondition or other empirical d
39、ata that relate the gas content ofcoal to such other parameters as coal rank, depth of cover, orgas emission rate.3.1.27 in-situ basis, adja basis in which gas content isdetermined from a plot of gas content versus bulk density(determined from open-hole high-resolution bulk density logdata). (1)3.1.
40、28 isotherm (sorption isotherm), nquantitative rela-tionship, at constant temperature, that describes how theconcentration of adsorbed phase molecules at an interfacialsurface varies as a function of system pressure. (1)3.1.29 lost gas time, ntime between when the sample gaspressure falls below the
41、reservoir pressure during samplerecovery (time zero) and the time when the sample is sealed ina desorption canister. (1)3.1.30 lost gas volume, nvolume of gas that is releasedfrom a sample (generally under conditions of decreasingtemperature and pressure) before it can be placed in a canisterand mea
42、sured (between the time when the sample gas pressurefalls below the reservoir pressure during sample recovery andthe time when the sample is sealed in a desorption canister).(1)3.1.31 macropore, npores in the coal larger than 50 nm.(3)3.1.32 manometer, nsee volumetric displacement appara-tus.3.1.33
43、measured gas volume, nmeasured volume of gasthat is released from a sample into a desorption canister,reported at standard temperature and pressure conditions. (1)3.1.34 mesopores, npores in the coal larger than 2 nm andless than 50 nm. (3)3.1.35 micropores, npores with a width of less than 2 nm.(3)
44、3.1.36 modified direct method, nmodification of the directmethod by the U.S. Bureau of Mines according to Diamondand Levine (4) and Diamond and Schatzel (5) to accountprecisely for changes in the concentration of gaseous speciesduring desorption, with particular applications to situations inwhich sm
45、all amounts of gas are evolved. (1)3.1.37 quick connect fittings, npipe fittings designed foreasy and rapid connection and disconnection.3.1.38 raw basis, nbasis for gas content calculationwhereby the gas volume is divided by the actual sample weightregardless of the moisture content or the presence
46、 of non-coalin the canister sample. (1)3.1.39 residual gas volume, nvolume of the total sorbedgas that remains in the sample after desorption into a canisterhas effectively ceased (after termination of canister desorp-tion).3.1.39.1 DiscussionResidual gas volume, as defined andreported, can be very
47、different for slow desorption and fastdesorption methods. Early termination of desorption followedby sample crushing will obviously lower desorbed quantities ofgas and increase the residual values. Maceral composition,lithotype composition, and the coal bench being sampled mayall affect permeability
48、 on small-scale samples. (1)3.1.40 sidewall core, nsmall diameter core taken down-hole by wireline methods using percussion or mechanicalmethods to drill into the side of the borehole.3.1.40.1 DiscussionThe percussion method cores by ex-plosively firing hollow core barrels into a coal seam and thenr
49、etrieving the coal plug to the surface. The mechanical methoduses hollow rotary drills to core into the coal seam and thenpull the core plugs back into the tool and then they areretrieved.3.1.41 slow desorption method, nvolumetric readings ofcanister gas content are taken frequently (for example, every10 to 15 min) during the first few hours, followed by hourlymeasurements for several hours, and then measurements on24-h intervals until no or very little gas is being desorbed foran extended period of time.3.1.41.1 Discussi
