Stress emission of helium and argon in coal seams Stress emission of helium and argon in coal seams

Stress emission of helium and argon in coal seams

  • 期刊名字:中国科学D辑
  • 文件大小:469kb
  • 论文作者:朱铭,周瑞光,尹代勋,高玉生,张福松,成彬芳,刘强,罗信华
  • 作者单位:Institute of Geology and Geophysics,Nantong Mining Bureau,Tianjin Investigation
  • 更新时间:2020-06-12
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论文简介

Vol 46 No 6SCIENCE IN CHINA(Series D)June 2003Stress emission of helium and argon in coal seamsZHU Ming(朱铭), ZHOU Ruiguang(周瑞光), YIN Daixun(尹代勋),GAO Yusheng(高玉生), ZHANG Fusong(张福松),CHENG Binfang(成彬芳), LIU Qiang(浏刘强)& LUO Xinhua(罗信华1. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China2. Nantong Mining Bureau, Chongqing 630802, China3. Tianjin Investigation, Design and Research Institute of Water Resources and Hydropower, Tianjin 300022, ChinaCorrespondenceshouldbeaddressedtoZhuMing(email.Zhmyr@sohu.com)Received December 17. 2002Abstract In the Yutianbao Mine, the Nantong Coal Field, Chongqing a lot of gas samples weremeasured and analyzed. It has been found in these samples that helium is sensitive to stress concentration, while argon is sensitive to stress release. Compared with the flowing out of gas itself, thecombination of helium and argon can be more suitably used as an indicator to predict gas outburstIn a mining area of this mine, both 8 He 30 and 8 Ar <-0.97 can be used critically to define thedangerous area. Also, the contour maps of 8 He, 8 Ar and CH can provide a guidance for engineering monitoringKeywords: helium, argon and its isotope, stress emanation, prediction of gas outburst, contour map, engineering geologyThe relationship between inert gas and geologic stress has been paid attention to by seis-mologists in the recent twenty years. Recent studies of seismic belts show that changes ofgeological stress can lead to emanation of inert gas from geological bodies F. In the studiedemanation of radon in a granite sample under stress in 1981, Holub et al. l found that it emitted alarge number of radon just under 1/2 o. In 1983, Honda et al. studied release effect of heliumand argon from various rocks under a uniaxial stress, concluding that the degas of squeezed sam-ples should primarily depend on new surfaces produced by expansion. These results show that therelease effect of helium and argon is only related to physical process of stress changes. Accordinto Ozima, the emanation of inert, such as helium and argon, due to a geologic dynamic process,is called stress emanation. Of course, an earthquake is a larger scale geological dynamic processThen, can the stress emanation be found in engineering geological scale? It is the problem to bediscussed in this paperIn engineering geological studies, one of the most interesting and important tasks is to evalu-ate and predict geological disasters threatening engineering projects. For this reason, monito中国煤化工)mw,theCNMHGSOft rock, kata-rock and clay rock. Moreover, even in hard rock, it is difficult to know real stress changesCoal is a soft rock and contains a lot of radiogenic helium and argon that had long beenSCIENCE IN CHINA (Series D)VoL 46accumulated owing to decaying of radioactive elements U, Th and K. In addition, a certainamount of non-radiogenic helium and argon (including the atmosphere-derived different geologi-cal periods ) could be trapped, therefore, the abundance of He and the isotopic ratio of Ar are farhigher in coal and gas than in atmosphere. In coal mining process, since the stress state and itschange in different mining positions are sometimes known, it is possible to establish the relation-ship between the stress state and the inert gas emanation. In the Longtan coal system, South Chinathere are a plenty of the suction holes, favorable for gas sampling in this study. Therefore, a coal-an ideal natural laboratory for studying the relationship between stress and helium andargon emanation in soft rockGeological background, sample location and analysis techniqueThe work area is located in the yutian bao mine of the nantong coal district. about 130 kmsouth of Chongqing City, China. In the Nantong Coal District the outbursts of coal and gas havebeen very serious. Since 1955, such accidents have happened more than 1200 times, includingtimes of bursting out 500-1000 t coal and twice of more than 1000 t. The Longtan coal system ofPermian ages here contains 7 bed coals, in which coal seams No 4 and No 6 are exploitable beds2.5-3.2 m and 1.5 m thick, respectively. In coal seam No 4 as the mainly mined bed, the coaland gas outbursts are frequent and serious, while in No. 6 they are accidentalMost part of the Yutianbao Mine is located in the Bamianshan syncline and its east and westflanks belong to the Yaqueyan shear fold zone and the Yutangjiao shear fold zone, respectively.Huge outbursts accidents have been focused near Fault Fl through the central part of the Bamianshan syncline and in the Yaqueyan shear fold zone. In order to decrease the danger of coal and gasoutbursts coal seam No. 6 has first been mined to relieve stress in coal seam no. 4. with miningof coal seam No 6, a different stress state occurs in coal seam No 4 (and it can usually be dividedinto four zones: the initial geo-stress zone (normal stress zone), the stress concentration zone, thetransitional zone, and the stress relieving zone). But as the further mining of the underlying coalseam No 6, the stress state in the overlying coal seam No 4 continued to vary. Although someng measures were adopted, the danger of coal and gas outburst accident has not beenreduced yet. In order to reduce such a danger as much as possible and to utilize gas as fuel, theextracting channels between No 4 and No. 6 were dug in a certain density, and then from thesechannels, the suction holes were drilled toward coal seam No. 4. A gas-extracting system was setup to utilize gas. It is the suction holes that provide us a good chance to collect gas samplesThe samples used in this study were collected from mining areas No 2602(30 m level) andNo, 3601(100 m level) of the Yutianbao Mine. In mining area No 2602 samples were collectedtwice, with an interval of 8 days. In addition, gas was t中国煤化工 machine channelNo3602 of the Yutianbao mine and airway No 2603 ofCNMHGAll samples of He and Ar were measured in site by a modified LZL-902 Quadrupolectrometer. The measurement technique had been described by Zhao Dongzhi et al.[s].TheNo 6STRESS EMISSION OF HELIUM ARGON IN COAL BEDAr contents and argon isotope in the local atmosphere were used as their standards. The measuredresults were calculated by the following formulasδHe=(He3Hea/HeδAr=( Ar-Ar2A8(40Ar/Ar)=[(Ar/6Ar)-(Ar/bAr)1/(40Ar/where s and a represent sample and air, respectively2 He, Ar and CH, in gas from exacting holes2.1 Strong emanation of helium in the stress concentration zoneHelium has two isotopes ' He and"He. The former is an ancient component and has a lowerbundance, only with an order of 10-6. He is transformed from the a proton emitted by decayinU and Th at the different stages. In fact, it is usually called He. Because U and Th are abundant incoal systems like in oil-gas fields, a lot of radiogenic helium could be formed, generally with anabundance of 10order, much more than its atmospheric abundance (5.24x10). Therefore, themixed atmosphere helium can be ignored. Helium has 4 protons and effective diameter of 0.2 nm,so it has a unique penetration and escape capabilityIn the previous work, some connection of stress with helium anomalies had been noted inthese coal mines 9, 10. From a three-dimensional picture(fig. 1 and table 1)based on 8 He valuesSampling siteCoal sean destressed I No 4)Suction helestress relieving zoneTransitional zoneExtractinchannelStress concentrition zoneDestressing coal seam (No,hInitial goo中国煤化工Undigged coal areaCNMHGSCIENCE IN CHINA (Series D)VoL 46of the first collected samples from the suction holes in mining area No 2602 in the YutianbadMine, it can be seen clearly that an obvious helium anomaly occurs at the stress concentrationzone of coal seam No 4, which is just above a stopping face of coal seam No 6. The second sam-pling and measuring in the same mining channel show that the peak value of 8 He moves with thestress concentration zone(table 1). For example, in hole 6-4 of coal seam No. 4, the measuredvalue was 49.12%, but after 8 days it decreased to 37. 12%. At the same time, the measured valuein hole 7-1 increased from 15. 43% to 56.24. It clearly shows that the helium anomaly of coalseam No 4 is progressively migrated with the stopping face of coal seam No 6(table 1). Theeak value migrated for 10 m, and at the same time the distance of the stopping face of coal seamNo. 6 is just about 9.6 m that is very close to the distance of two peak valuesTable 1 Measurements of helium, argon and coal gas from the extracting channels in the Yutianbao and Donglin coal Mines, NantongHole ch4(%)δ He SAr CH(%)δHeδ Ar Hole CH(%)δHeδArCH(%)δHeδAr0.0080.003.26-09107-20.001.42-0.1504-3100.003.170.88100.003.260.8907-34465.004.40-0.80.000.500.12090.002930.7407-520.001180-0.14042003980.1304596.003.00-093100.00240-0.850760.005.58-0.026100.002.33-0.3607-70.12016.003,40-0.044740.001.850.407-80.090.0480.000.61-0.0775-180.004.850.85100.002430.3208-140.00-0.32-0.0805-330002.890.72-0.0280.000.35-0.0645401284560180085-691000.9098000960.7108-50.001.08-0.09620360.9896.004.69-0.8808-746.000.520.0014.060.3408-80.003820.1506445.0049.12_0.4715.0037.160.4509-1850063.80-0.8706-660.0012.300.5520.00717-0.2309-21000010580-0.6006-7100.003.31-095100003.41-0.8509-392.00259104407-112.0015.43-0.2378,0056.24-0.660941000063.90-0.81047960.279-243.000.83-0.508.350.994-6100.0067.050969-50.000.04-0.0100.003.75-0.979-675.00148-0.762.30_0.879-72.000.10-.083-4I00.0034.74-0.918-172.00468-0.852-1100.001.400.478-260.0021.82-0.628-33.00778-0.121508-49.00489-0.111-295.002.15-0.8434.20-0.09中国煤化工145.002910.45CNMHGo compare the results from other extracting holes, a series of contour maps of helium, argonand methane are reproduced in fig. 2. The distribution of helium anomalies varies in the differentNo 6STRESS EMISSION OF HELIUM ARGON IN COAL BED551mining districts. For example, it can be seen that the helium anomaly occurs not only in a stressconcentration zone, but also in the stress restoring zone(fig. 2-d3) moving 150-200 m apart fromthe stopping face.ArAr75oHe50物圖2602(1)2602(2)360Fig. 2. Contour maps of SHe, 8 Ar and CH, from the extracting channels in Nantong Coal Field. bl, cl, dl, A-A'correspond toA-A-A""/in fig. l, but in al AA passes through the peak of argon2.2 Argon's composition and isotopes as an indicator of stress release degreegon in coal gas is an important composition to p中国煤化he stress state inthe coal body as well. It consists ofISotopes bAr. 32Ar 3 Ar are twoCNMHGnon-radiogenic and ancient components of the Earth andgullit Conponent decayedby 4K. At the early stage of the Earth, 40 Ar was scarcely accumulated. According to the nuclear552SCIENCE IN CHINA (Series D)VoL 46synthesis theory, Cameron gave a40Ar/Ar ratio of 2 x104. Based on isotope argon dating dataof meteorites, Wang Songshan! 2 3 gave an average initial 40 Ar/6Ar ratio of 0.94 4, approximating to 0.83 from lunar samples by Turner. et al. 5 and Pepin et al. b. Therefore, it is reasonable that the initial+Ar/Ar ratio at the Earths early stage is considered to be smaller than 1. Notonly the theoretical models about atmospheric evolution by Ozima!, Hamanoll8, and Hart!l9,butalso the laboratory study by Wang Songshan UI show that for long earth history has continuouslybeen producing #Ar, a part of which entered into the atmosphere, making the 4 Ar/Ar ratio in itincrease from less than I to 295.)As in natural gas, argon in coal and gas is of multiple sources 21. There are mainly three resources,radiogenic argon, a product of decaying of K in potassium-bearing minerals in the coalsystem; inherited argon, which had been contained in the detrital minerals before coal deposition;atmospheric argon, in which coal has trapped from ancient air and modern air influenced by mining and sampling. Here, for convenience, air before mining and sampling is called ancient air, andthat after mining and sampling called modern airTherefore. we havergrr++Ar:+40ArAr=36Ar +36A1where g, r, i, and aa represent gas in coal gas, radiogenic source, inheriting source, ancient atmospheric source, respectively. In fact, expectation for radiogenic 4Arr, both inherited; and ancient atmospheric 4 Ara are non-radiogenic argon, which is indicated by subscript o. So formulas(4)and(5)can be rewritten intorg=Ar。+ArThrough formula(6)divided by formula(7), we have an isotopic argon ratio in coal and gas(Ar/Ar)g=(Ar/Ar)o+Ar/ArIn fact, the component of argon in the samples from the gas extracting holes is the mixture ofgas in coal and modern air. Thus, we haveArs=Arg+Arewhere s, g, ae represent samples, gas in coal and modern air, respectively. Because the abundanceof argon is much more in modern air(0.93 x10-2)than in coal (1010), that mixed in informula(9)has a significant effect on the total argon Ars in a sample. The smaller the atmosphericargon, the smaller the sample Ars. Hence, the sample Ars is substituted into formula( 2 ), and 8 Ar issmaller too(more on the negative side). On the contrary, if what extracted from the suction hole ismainly modern and contains smaller gas, the Ars value. X Ar ic larger too(more on the中国煤化工positive side).According to formula(9), we haveCNMHGNo 6STRESS EMISSION OF HELIUM ARGON IN COAL BEDArs=3Ar2+“Araeand finally(0Ar/6Ar)=(0Ar/36Ar)+(4Ar/6Ar)Due to the value of the isotopic ratio(Ar/Ar)ae= 295.5 in modern air, it can be known frorformula(12) that the more the gas in the suction hole, the less the argon mixed in modern air, thecloser the (40Ar/bAr)s approximates to (Ar/bAr)e, and the higher the (40Ar/bAr)s(The accumulation of the radiogenic 40Ar makes the isotopic ratio of (Ar/6Ar) in coal much more than 295.5in modern air), and vice versaFrom fig 2-al, bl, and cl, it can clearly be seen that the high value area of (o Ar/6Ar), thelow value area of 8 Ar, and the high value area of coal gas are identically located in the part ofstress release areas. Therefore, the composition and isotopes of argon are indicators of stress release degree2.3 Helium, argon and methane in different stress zonesIn initial geo-stress zone(the normal pressure zone), coal has a poor gas permeability because of scarce fractures, so the concentration of gas is very low in the suction hole, and the samplargon is mainly from air in the suction hole, resulting in a larger value of 8 Ar(toward to O)and alower isotopic ratio. In this situation, the emanation of helium is also weak. If the environmentwas completely closed, 8 He, 8 Ar and CH all would approximate to zeroIn the stress concentration zone, coal has some fractures and releases a certain gas, so thesamples exacted may have relativelymuch Ar and CHa. The effectiveSHediameters of helium, argon and500methane are 0.2. 0.28 and 0.32 nm(Ar1Ar)1400respectively. The penetrating capabilityof helium is the strongest. when fractures do not permit argon and methane0.0100to pass, helium anomalies may occur.0.2In the transitional zone and therelieving stress zone, the concentration40of gas from coal is very high in the-0.8 CH4suction hole so ar. mixed in the sam-ple is smaller. When CH4 in the sampleDal(CHa in-Stress concen- Transitionalstress zone tration zonecreasing from 40% to 100% in fig. 3),argon in the sample is also comp letely Fig3.Ema中国煤化工curves are macC N MH Gf fig I and in AAArg. Consequently, the isotopic ratio of in fig. 2.Theare from 36, -85 to 36, 85 for SHe, SAr, and CH.( Ar/Ar)g has the highest value and and from 25,-85 to 25.85 for("Ar/"Ar),SCIENCE IN CHINA (Series D)VoL 46S Ar varies from 0 to -1, which is to some extent what the initial radio should be shown. alsobecause helium is first released in the stress concentration zone, it decreases apparently in thesetwo zones(fig. 2-d1, d2 and d3)8 He, 8 Ar, (Ar/Ar)s and CH in different stress states are shown in fig 3. It shows that theemanation of helium is obvious in the stress concentration zone, but the peak of isotope argon isexhibited in the stress released zone. The relationship between argon( Ar) and methane is netively correlated2.4 Distribution of 8 He, 8 Ar and CH4 in contour mapsIt is generally thought that the normal stress zone(initial geo-stress zone), the stress concen-tration zone, the transitional zone, and the relieving stress zone should be distributed in order. Butfig. 2 shows that their distribution is not so simple. Distribution characteristics are as follows(1) There is a good correspondence between the gas concentration area and the argon concentration area, as shown in fig. 2-b1. b2. b3 and fig 2-c1. c2 c3(2)The distribution of He, Ar and Ch is heterogeneity in coal. Sometimes, although theyoccur in the stress concentration zone, yet it just has the features of the normal stress zone. In fi2-c2, for example, in coal seam No. 4 there is a strip oblique block with the stopping face and cha0 area. This position is just in the stress concentration zone, but its low CH4 should have theharacteristic of the normal stress zone Therefore all of these suggest that in coal body the realstress state is very complex and its complication may be shown in the contour maps of HeCH4( The axis and boundaries of closed contour lines in the contour maps have certain directivity, as shown in fig. 2. Typically, such an axis is oblique to the stopping face, forming an"Xpattern. This directivity means that the distribution of He, Ar and CH, may be controlled not onlyby the stress derived from the mining process, but also by the original stress so that their distribu-tion reflects the effect of the original stress. Similar cases have been seen in contour maps of heli-um and argon of oil-gas fields 23 He and Ar in gas from drilling holes of the stopping face3.1 He and Ar in the compressed tectonic areaMining area No 3206 is just located within the Bamianshan broad syncline. a bland fault Flwith the fault displacement of 2-9 m passes through this mining area. According to geomechanics, the upper part of the syncline is in a compressive state, while the lower part is in a tensileburst of 13 t occurred at the place 85中国煤化工 the west side ofFl, and after 6 days the second coal outburst occurredCNMHGat the place 3ing from the east to the west thtotal headway of 10 holes is 120 m, with sampling once l m apart. At every sampling site, theNo 6STRESS EMISSION OF HELIUM ARGON IN COAL BEDfollowing items were observed or measured: gas flow @(/min), drill cuttings S(kg/m), coal tensile intensity o(MPa), temperature t(C), helium and argon Their average values of each hole arelisted in table 2 Plots of helium and argon against other parameters are shown in fig 4Table 2 Averages of He, Ar, drill cuttings(S), coal tensile strength, gas flow(@), temperature(n) measured at districts 3602 and 2603of the yutianbao mine8He(%)8Ar(%)S/kg/mMPa0.21189726.9519.050.796.962345678901234567890.765.5217.84640.740.9432.146.l0.6431.7516.180.3232.350,480.41330.1331.560.419.26040.670.850.4124.470.740.550.870.7616.1223.300.380123456780.824.4112.990.432.461.670.540.8318The following relationships can be seen from fig. 4(1)8 He with 8 Ar is of a negative correlation(fig. 4-1)(2)Drill cuttings(S)with 8 He are of a positive correlation, but these with 8 Ar are correlatedin a quadratic curve(fig. 4-2a, 2b)(3) Temperature(t)with 8 Ar is of a good positive correlation, but that with 8 He is correlat-ed in a quadratic curve(fig. 4-3a, 3b)(4)Gas flow(@) with helium is correlated in a quadratic curve, and so are the gas flow andargon(fig. 4-4a, 4b)中国煤化工Again from the two-and three-dimensional diagraCNMH Ge seen thatδHand 8 Ar are medium values when the gas flow(@)is maximum. This is a very important phenomenon. For a long time in the current prediction of gas outburst, the gas flow has first beenSCIENCE IN CHINA (Series D)VoL 46Oar(%)0.6SHe(6S/kgSAr(%o)SHe(%)4-3b「3043a1241.0d He644a5SAr%)oHe(%o)1.24-5a4-5b‰0.4Ar(%)SHe(%)Fig 4. Correlation plots of He, Ar, with drill cuttings (S), temperature(n), gas flow(@), tensile strength(o) from the compressive tec-tonic areachosen to utilize as a predictable indicator but to do so often leads to troubles. Sometimes, the gasflow exceeded the dangerous threshold, but no accident occurred. However, the gas flow was verylow, but a huge disaster happened. This problem could not be explained for a long time. Now theabove study can give an updated explanation. The study shows that the position of the outburstaccident of coal gas is the very place where the stress中国煤化 y moment justbefore gas outburst, the coal body is not brokenCNMHG3). Only after the stress is released, a large amount of ga2, c3 and fig. 3)Unfortunately, in the past, as helium in coal seams cannot be measured in coal mining processNo 6STRESS EMISSION OF HELIUM ARGON IN COAL BEDpeople know a little about the real relationship between the coal gas flow and the stress while At isaround the crack of the coal body, therefore, people do not pay attention to the significance ofsmall gas flow before the energy suddenly released, Hence this is the reason why small gas flowcan result in large, even huge accident. It shows that it is certainly unreliable to use gas flow @)as an indicator to predict the outburst accident. Helium reflects the stress better than the gas flowAs a sensitive indicator to predict the outburst of accident, Helium is obviously superior.(5)Correlations of coal tensile intensity (o)with other parameters are weak(fig. 4-5a, 5b)The above discussion indicates that the parameters of helium, argon, temperature and flowquantity of detritus can be used as the main marks for predicting the outbursts of coal and gasWhile the flow quantity of coal gas is only a reference mark, and it seems that to work out theension intensity of coal is rather difficult3.2 He and Ar in the tensile tectonic areaAirway No 2603 was previously thought to be located in a compressive area of the Yaqueyanshear fold belt. The huge coal and gas outbursts happened 9 times there. This airway has longbeen considered so dangerous as to forbid mining. At the beginning, therefore, our work indeedtook grave risk, but we soon found out the following phenomena that surprised us(1) The gas flow is much higher than that in mining area No 3602 as a compressive tectonicarea, but no gas outburst occurred in spite of the gas flow in many holes exceeding any criticallevel(table 2)(2)Helium is much lower than that in a compressed tectonic area or even lower than itsatmospheric abundance, therefore 8 He is negative(table 2, fig. 5)(3) Argon and helium have a very good correlation(4)The temperature of coal is higher.Open tensile systemUnstable Menacing dangerousHole No. 1 a Hole No. 2 A Hole No. 3 o Hole No 4for channel No 3602v Hole No5 x Hole No 6 Hole No. 7 Hole No 8 Hole No 9 w Hole No 10FIxed lineThe boundary of the points testedfor channel No 2603中国煤化工Fig. 5. Dangerous degree-based division of a stopping faceCNMHGAll of them show that it is impossible for the abrupt gas outburst to occur at any rate. Ittrue during the month of our work. We took this month to complete 18 holes and drill down 120 mSCIENCE IN CHINA (Series D)VoL 46The data observed and measured are listed in table 2. At the same time we observed in this airwaythat there are well-developed fractures and crossed calcite veins in coal, showing characteristics ofa tensile tectonic area. Later we found that this airway is actually located in a tensile part of thehinge of a small recumbent fold (on the tensile side of the center of the fold ) Therefore, there aremany different features of the parameters from compressive area. In tensile tectonic position thereare many passage good channels so that a lot of coal gas flows from near rich coal gas sectionDue to a lot of coal gas pass there the pressure in coal body is higher than that around air envronment,so atmospheric component cannot pour back to coal gas system of coal body. At thesame time, as mass of helium is smaller than methane, helium can diffuse easily to atmosphere. Atthe end, helium in coal gas is smaller than that in atmosphere for a tension area3.3 Significance of helium and argon in gas used as indicators to predict gas outburstAll of discussions above show that the technique of determining helium and argon will playan important role in predicting coal gas outburst accident. Helium is a sensitive detector to stresschanges whereas digging process and argon are other marks to estimate the releasing degree ofstress and broken coal body. However, it is possible to establish the indicators to predict the sud-den outburst accident by utilizing helium and argon methodsThe site of the first sampling hole in mining area No3602 is only 3 m apart from the point ofa gas outburst and hence the values of 8 He and 8 Ar from this hole have especial warning signifi-cance S He is from 23. 4% to 28.6%, averaging 24.7% and S Ar is from -0.83% to-097%, averaging -0. 88%(table 2). These values are either maximum or minimum compared with those fromother holes. Moreover, the drill cuttings(10.1 kg/m)and the temperature(2021 C)from this hole(table 2) have extreme values too. Therefore, it is reasonable to choose such values of 8 He and8 Ar to define the menacing area of gas outburst( For rounding, the range of 30<8 He 22.5-0.97>8Ar>-08 is used ) Hence the values of 8 He>30 and 8 Ar<-0.97 can be consideredas the indicators of a dangerous area(table 3). For the most holes, the values of 8 He and 8Arfrom holes Nos. 2, 3, 4, 5, 6 and 9 are in a range of 22 5-12. 5 and -0 5---0.8 (fig. 5). In somepoints, values of S He lager than 22.5 are in the threatened area and others smaller than 12.5 are infe area, so the area is ascribed to an unstable area. The rest of compressive areas and all of thetensile tectonic areas can be ascribed to the safe area(fig. 5)In conclusion, the relationship between the values of 8 He and 8 Ar and the outburst accidentof coal gas in the different tectonic areas is described in table 3Table3 Value ranges of helium and argon used to divide different areas of danger degree in the different tectonic areatectonic area SecurityGas outburst中国煤化工 dangerous degreedangerous area095Closed pressed areaCNMHG5-0.5-0.812.5areaOpen tensioneakage area0-0.1-09—0No 6STRESS EMISSION OF HELIUM ARGON IN COAL BED4 Conclusions(1) In the stress concentration zone in coal, helium emanation is the strongest. The locationof helium emanation moves as stress changes and the intensity of helium emanation is related tothe stress size(2)The composition and isotopes of argon are sensitive to stress release(3) Helium and argon can be more suitably used as indicators to predict gas outburst than gasself(4) The contour maps of helium, argon, and methane can provide information on local stressstate favorable for engineering monitoringAcknowledgements When working in the Nantong Mine, we got help from Senior Engineers Li Zongjian, XieMengzhang, and Lei Shaoyun, and Engineers Luo zhaolin, Cai Chunxiang, Wang Xiaochun, Li Qiulin, Zhao Supping, ChenZongqin, Zhao Shengfang, and Huang Jingwei of the Nantong Mine Bureau. During 1986-1990, Senior Engineer ZhaoDongzhi and postgraduate Tan Jun in the Institute of Geology, CAS, participated in early work and finished a lot of measurementand basic examination. 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