采矿学王庄煤矿论文设计

第第页英文原文DevelopmentandapplicationofreservoirmodelsfortheevaluationandoptimizationoflongwallmethanecontrolsystemsC.Ö.Karacan,W.P.Diamond,S.J.Schatzel&F.GarciaABSTRACT:Methaneexplosionshavehistoricallybeenoneofthemajorcausesoffatalitiesandinjuriesinundergroundcoalminingoperations.Advancednumericalmodelsandpredictivemodelingapproacheshavethepotentialtoofferoptimizedmethanecontrolsolutionsforgeneralmineplanningpurposesandtoaddressspecificmethane-relatedoperationalproblems.Thispaperdescribesthedevelopmentofreservoirmodelsforthelongwallminingenvironmentandtheirapplicationforinvestigatingtheinfluenceofvariouscompletiondesignparametersonthemethanedrainageeffectivenessofgobgasventholes.TheinfluenceofincreasinglongwallpanelwidthontheeffectivenessofcurrentgobgasventholecompletionandplacementstrategiesinthePittsburghCoalbedwereevaluatedandoptimizeddesignsdevelopedtocapturetheexpectedincreaseinmethaneemissionsonthelargerpanel.1INTRODUCTIONComprehensiveassessmentsoftheneedforadditionalmethanecontrolcapacitybeyondventilationoftenrequirebothanempiricalandtheoreticalapproachforanadequateortimelycontrolofincreasedmethaneemissionlevels.Thus,thepredictionofmethaneemissionsandoptimizationofmethanecontrolsystemspriortostartinganewminingoperationwillbeamajorimprovementtowardseliminatingtheexplosionsintheundergroundworkplace.Duringlongwallmining,thecavingofimmediatestrataandstressreliefcreatehorizontalfracturesalongbeddingplanesandverticalfracturesinthestrataoverlyingthecavedzone.Thesefracturesprovideanextensivepathwayforgasmigrationfromthesurroundingcoalbedsandothergasbearingstrataintothelongwallminingenvironment(Fig.1).ThethickNessofthefracturedzonecanvaryupto100timestheheightoftheminedcoalbed(Palchik2003).Thefracturedandcavedrockmassleftbe-hindtheadvancinglongwallfaceisgenerallyreferredtocollectivelyas“gob”(Fig.1).Themethanethatoriginatesandaccumulatesinthegobabovethemined-outlongwallpanelisthemainsourceofpotentialgasemissionsduringlongwallmining.GobgasextractionintheNortheasternU.S.isalmostexclusivelyaccomplishedusingventholesthataredrilledfromthesurfacetowithinashortdistance[typically10-15m(30-45ft)]ofthecoalbedbeingmined(Diamond1994).Commonly,thebottomsectionofthewellcasing[generallyabout60m(200ft)]isslotted.Thegobgasventholesgenerallybecomeproductiveonlywhenthemining-inducedfracturesarecreatedasminingadvancesundertheventhole(Diamond1994).Figure1Schematiccross-sectionviewofsubsidedstratazonesandmethanecontrolsysteminfluencezonesabovemined-outlongwallpanel(Muchoetal.2000).Numericalmodelsoffereffectivecapabilitiesforpredictingmethaneemissions,anddesigningdrain-agesystemsaccordingly.Therehavebeenreportedstudiesusingcomputationalfluiddynamics(CFD),boundaryelementandfiniteelementmodeling(FEM)techniquestobettercharacterizetheparametersforgasemissionprediction[Ren&Edwards(2002),Lunarzewski(1998),Tomitaetal.(2003)].Reservoirsimulatorsdevelopedovertheyearscanrepresentthecomplexreservoirflowmecha-nismsincoalbeds(King&Ertekin1991).However,acomprehensivereservoirmodelcapableofrealisticallyrepresentingvariousaspectsofminingoperationsandproductionfromgobgasventholeshasnotpreviouslyexisted.Inonestudy,Zuber(1997)modeledthefaceandribemissionsduringdevelopmentmining.Karacanetal.(inprep.,2005)andEsterhuizen&Karacan(2005)havedeveloped“dynamic”reservoirmodelsthatincludethesubsidedstrataabovetheminedpanelduringlongwallminingtoevaluatemethaneemissionsandvariousgobgasventholedesignfactorsfortheiriMPactongasdrainageefficiencies.2MODELDEVELOPMENTThemodelssummarizedinthispaperweredevel-opedforminesitesoperatinginthePittsburghCoal-bedintheSouthwesternPennsylvaniasectionoftheNorthernAppalachianBasin.ThereservoirmodelswereconstructedusingComputerModelingGroup’s(2003)GEMcompositionalreservoirsimulator.2.1GeneraldescriptionoftheminesitesOverburdendepthsinthearearangebetween152and274m(500and900ft).Longwallpanelsintheoldminingdistrictsofthisminewerearound253m(830ft)wideandwereincreasedto305m(1000ft).Inthenewdistricts,thepanelwidthswereoriginally430m(1250ft);however,thefirst480m(1450ft)widepaneliscurrentlybeingmined.Thus,allthepanels,particularlytherecentones,aresuper-critical,whichresultsinamorecompletecavingoftheoverburdenstrataintotheminevoid.AgeneralizedstratigraphicsectionforthestudyareaisshowninFigure2.SeveralcoalbedswithacombinedthickNessofalmost3m(10ft)arepresentinthe26m(85ft)ofstrataimmediatelyabovethePittsburghCoalbed.Withinthisinterval,thethickestcoalbedistheSewickley,whichisabout25m(75ft)abovethePittsburghCoalbed.Betweenthesetwomajorcoalbeds,therearecoMParablythinPittsburghridercoalsandthediscontinuousRedstoneCoalbed,whicharecontainedinthecavedzoneafterpanelextraction(Fig.1).Thegasemissionsassociatedwiththecavedzonereporttothebleederventilationsystem(Muchoetal.2000).InsomepartsofthestudyareaasandstonepaleochannelreplacestheshaleunitusuallypresentabovethePittsburghCoal-bed.ThethickNessofthepaleochannelvariesbe-tween0-13m(0-40ft).Regionally,theSewickleyCoalbedmaysplitintotwoseparatebenches,anditsheightabovethePittsburghCoalbedmayvary.Gascontainedinthefracturedzone(Fig.1),inparticular,gasintheSewickleyCoalbed,primarilyreportstothegobgasventholes,iftheyarepresentandopera-tional(Muchoetal.2000).Figure2.AgeneralizedstratigraphicsectionofthestrataabovethePittsburghCoalbedinthestudyarea(Muchoetal.2000).2.2GridmodelgenerationforlongwallsitesInordertomodelthelongwallminingprocessandanalyzetheassociatedmethanecontrolsystems,athree-dimensionalgridmodeloftheminesitehastobecreated.Thehorizontaldimensionofthegridmodelswereusuallydeterminedbasedontheproblemtypeandthetotalareaofinterest.ThenumberofverticallayersandtheirthickNesseswerebasedongeneralizedstratigraphicsectionsfortheminesite.ThePittsburghCoalbed(mining)layerwasconstructeddifferentlyfromtheotherlayersinthegridmodeltohostboththeminedandunminedPitts-burghCoalbed,andtheentriessurroundingthelongwallpanels.AnexampleshowingthisstructureforoneofthestudysitesisgiveninFigure3.Figure3.PittsburghCoalbedlayerasrepresentedinthemodels.2.3Gobgasventholesandthepseudo-ventilationsystemAsimplifiedversionoftheventilationsystemwasincorporatedintothemodel.Foreachpanel,asetofwellsinjectingairintotheentrieswitharateconstraintof1700m³/min(60,000cfm)representedtheairintakepartoftheventilationsystem.Theexhaustingbleederfanatthetopofa1.8-m(6-ft)diameterairshaftwasmodeledwithalarge-diameterverticalwellonthetailgatesideofthepanelandoperatedwithabottom-holepressureconstraintof1.36KPa(0.2psia)negativepressure.Thelocationsofgobgasventholesinthemodelweredeterminedbasedontheirlocationsonthestudypanels,andtheywereconfiguredbasedontheiractualreportedcompletiondata.Theventholesareusuallydrilledtowithinabout12-13m(40-45ft)ofthetopofthePittsburghCoalbedatthisminesite,and17.8-cm(7-in)casing,with61m(200ft)ofslottedpipeonthebottomisinstalledasshownforVentholeA,Figure1.However,insomecase,theventholesweredrilledclosertothemininghorizonandintothecavedzone(VentholeB,Fig.1),whichaffectstheirperformance,aswillbediscussedinthefollowingsections.2.4GeomechanicalcalculationsforstrataresponseandpermeabilitychangesThegeomechanical,fastlagrangiananalysisofcon-tinua(FLAC)model(IthascaConsultingGroup,Inc.2000)wasusedtoevaluatetheeffectsoflongwallminingonthesurroundingrockmassandtocalculatemining-relatedpermeabilitychanges.CalculationofpermeabilitychangeswasaccomplishedusingthefinalstressandrockfailuredistributionsfromtheFLACmodelruns,andemployingempiricalrelations[Ren&Edwards(2002),Lowndesetal.(2002)].Detailsofthemodeldevelopment,permeabilitycalculations,andgeomechanicalanalysisaregiveninEsterhuizen&Karacan(2005).2.5Simulationandmodel-calibrationstrategyDuringlongwallmining,thestratadisturbancesandtheonsetofproductioninsuccessivegobgasventholesmovealongwiththeface,Thisleadstoamoving-boundaryprobleminmodeling,whichwasaddressedwith“restart”models.Eachmodelrestartrunwasperformedsothatitwouldprogressuptoeitherthenextventholelocationortoadefinedlocationonthepanelforthedistanceandtimecharacterizingtheinterveningfacemovement(Karacanetal.inprep.).Thereservoir-parameterchangeswereincorporatedintothemodelasthefacewasadvancedbetweenrestartsduringcalibrationandpredictionruns.3MODELAPPLICATIONSFigures4and5showthetwogridmodelsconstructedforthisstudy.Inbothfigures,onlythecoal-bedsaredepictedtoimprovethevisualization.Themodelswerecalibratedbymatchingthemeasuredgasproductionrates,methaneconcentrationsintheproducedgasstream,andtheflowingbottom-holepressures.Figure4.StudymineCase-1,gridmodelofamulti-panelminingsite,PittsburghCoalbed.Figure5.StudymineCase-2,gridmodelofanewmin-ingdistrict,PittsburghCoalbed.Case-1(Fig.4)wasdevelopedforaprevious,multi-panelminingdistrict,andwasusedtoevaluatetheinfluenceofvariousgobgasventholecompletionparametersonmethanecapture.ThegridmodelshowninFigure5(Case-2)wasdevelopedforthenewminingdistrictthatstartedwith381m(1250ft)-widepanels,butwouldbeswitchingto442m(1450ft)-widepanels.ThefocusoftheCase-2studywastoestimatetheincreaseinexpectedmethaneemissionsandtoinvestigatealternativegobgasventholecompletionandplacementscenariosonthelargerpanel.3.1Case-1,Evaluationofgobgasventholecompletionparameters3.1.1Effectofslotted-casingdiameterThestandardcasingdiameterforthegobgasventholesinthestudyareawas17.8cm(7in).Theeffectsofdifferentslotted-casingdiameters[25.4cm(10in)and10.2cm(4in)]onmethaneproductionwereevaluated.ThelengthoftheslottedcasinganditssettingdepthabovethetopofthePittsburghCoalbedwereheldconstantattheiroriginaldesignvalues,61m(200ft)and12m(40ft),respectively.ThemodelingresultsgiveninTable1forthesimulatedminingperiod(910days)predictthatthecumulativemethaneproductionusingthe25.4cm(10in)casingwillincrease4.9%,ascoMParedtothe17.8cm(7in)standarddiametercasing.Theamountofmethaneproducedwiththe10.2cm(4in)casingwasabout6.7%lessthanthatproducedwiththe17.8cm(7in)diametercasing.However,theamountofmineairproducedwiththe10incasingwas12.3%more,whichresultedinalowerpredictedmethaneconcentration.Conversely,theamountofmineairproducedwiththe10.2cm(4in)diametercasingwas15.2%less,ascoMParedtothestandardcasing,whichresultedinhighermethaneconcentrations.Thepredictedincreaseincumulativemethaneproductionwiththelargerdiameterwellborewasduetotheincreaseintheopen-to-flowareaofthewellbore.Also,withlargerdiameterwellbores,thecalculatedpressurelosseswerelesscoMParedtosmallerdiameterwellbores.Thepredictedreductioninmethaneconcentrationwiththe25.4cm(10in)diametercasingismostlikelytheresultofmoremineair.However,sincethetotalpredictedgasproduction(methaneandair)washigherforthe25.4cm(10in)diametercasing,itstillresultedinhighercumulativemethaneproduction,eventhoughthemethaneconcentrationwasless.3.1.2EffectofslottedcasinglengthToevaluatetheinfluenceofthelengthofthecompletionintervalongobgasventholeperformance,thelengthoftheslottedcasingsectionwaschangedinthemodelto30.5m(100ft)andto76.2m(250ft),ascoMParedtotheoriginal61m(200ft)length.Thecasingdiameterwaskeptat17.8cm(7in),andthesettingdepthof12m(40ft)abovethetopofthePittsburghCoalbedwasmaintained.Themodelingresultspredictthatthecumulativemethaneproductionwillincreasewithincreasesinslottedcasinglength(Fig.6).Themethaneproductionwith76.2-m(250-ft)ofslottedcasingwas459.4MMscf,ascoMParedto391.8MMscfwiththestandard61-m(200-ft)ofslottedcasing.Thisdifferencecorrespondstoa9.5%increaseinmethanecapturefromthefourpanelsmodeledinCase-1(Fig.4).However,whentheslottedcasinglengthwasshortenedto30.5m(100ft),thepredictedmethaneproductiondecreasedto314.7MMscf.3.1.3Effectofslotted-casingsettingdepthTheeffectofcasingsettingdepth(distancefromthetopofthemininglayer)ongasproductionwasinvestigatedbymodelingalternativecompletiondepthsof19.8m(65ft),7.6m(25ft)and4.6m(15ft),ascoMParedtotheoriginal,12m(40ft)depth.Inthesealternativecases,the7.6m(25ft)completiondepthgenerallycorrespondedtoacloseproximitytothecavedzone,whichwasmodeledas7.3m(24ft)abovethePittsburghCoalbedfortheCase-1studysite,andthe4.6m(15ft)depthcorrespondedtocircumstanceswheretheventholewasdrilledintothecavedzone.The19.8m(65ft)completiondepthcorrespondsstratigraphicallytoadepthslightlybelowtheSewickleyCoalbed(Fig.2).Forthesescenarios,thecasingdiameterandslottedcasinglengthswerekeptattheiroriginaldesignvalues,17.8cm(7in)and61m(200ft),respectively.Raisingtheslottedcasingsettingdepthto19.8m(65ft),ascoMParedto12m(40ft),abovethePitts-burghCoalbedresultedina4%predictedcumulativemethaneproductionincrease.Thepredictedcumulativemethaneproductiondeclinedbyabout5%and29%whenthecasingwassettowithin7.3m(25ft)and4.6m(15ft)ofthetopofthemininglayer,respectively.Inthe15ftsettingdepthscenario,thelowerslotsofthecasingwereinthecavedzoneinfluencedbythemineventilationsystemwhereflowresistancewassmall.Therefore,theventholespulled74%moremineair,ascoMParedtotheoperator’sstandard~12m(~40ft)settingdepth.Sincemostoftheproducedgaswasmineairatthe4.6m(15ft),theaveragemethaneconcentrationinthecumulativeproducedgasattheendofminingwasabout40%,asopposedto60-70%averagemethaneconcentrationcalculatedforotherdepths.4SUMMARYReservoirmodelinghasbeenshowntobeavi-ableapproachforevaluatingmethaneemissionandcontrolissuesinthelongwallminingenvironment.Thisapproachisfarsuperiortothetraditionaltrial-and-errormethods,andhasthecapabilityofaddress-ingunexpectedmethaneemissionproblemsastheyevolve.

中文译文长壁工作面瓦斯抽采模型的开发和应用摘要：瓦斯爆炸历来一直是地下采煤工作的主要伤亡事故。先进的数字模型和预测建模方法有很大的潜力为一般矿区的规划和解决特殊的瓦斯相关的操作问题来提供最佳的瓦斯控制解决方案。本文介绍了储层模型的发展对于长臂采煤的环境及其应用来调查在采空区瓦斯排放孔的瓦斯抽放效果的各方面参数的影响。增加了长臂面板宽度的影响对于匹兹堡煤层目前的采空区瓦斯排放孔的完成和布局策略的评估和优化设计来捕获瓦斯排放量较大的面板上的预期增值。1介绍对于额外的超出通风设备能力的瓦斯控制需要综合评估，往往需要充足的经验和理论上的方法来控制瓦斯排放水平的增加。因此，预测瓦斯排放和瓦斯控制系统的优化来开始一个新的采煤方法之前将是朝着消除地下爆炸的主要改善工作来进行。在长臂采煤期间，直接顶的垮落与水平裂隙和垂直裂隙在沿层理方向上的应力消除造成上覆地层的塌陷。这些裂隙为长臂采煤环境中的煤层瓦斯移动及其他含气地层提供了一个广阔的途径。断裂带的厚度可以使开采煤层的高度变化达到100倍。裂隙和塌陷的岩体留下的长臂工作面一般称为“采空区”。瓦斯在采空区上方的产生和积聚是长臂开采过程中潜在的气体排放的主要来源。在美国东北部，采空区的瓦斯抽取几乎完全是通过地表与开采煤层之间短距离的通风孔进行排放。通常，井底的套管底部是有开槽的。采空区瓦斯通气孔产生作用一般只有才采动裂隙是产生在气孔挖掘的发展上。图1陷落底层采空区瓦斯控制系统剖面图数值模型预测的瓦斯排放量提供有效的能力，并以此设计相应的排水系统。有研究报道指出，采用计算流体动力学、边界元和有限元建模技术能更好的描述瓦斯涌出量的预测参数。储层模拟器多年来可以表示复杂的煤层储层流动机制。然而，一个能够实际的代表在采空区瓦斯通气孔进行采矿作业和生产等多方面的储层模型在以前是不存在的。他们开发了动态的储层模型，包括塌陷地层上方的长臂开采来评价瓦斯排放和各种采空区瓦斯通气孔设计因素对瓦斯抽放效率产生的影响。2模型的发展本文中介绍的模型总结了阿巴拉契亚盆地北部、宾夕法尼亚西南部的匹兹堡煤层的发展。这个储层模型是用计算机组成模型建立的储层模拟器。2.1开采地点的描述埋深的覆盖区域范围在152到274m之间。该矿区的老采区长臂工作面从253m增加到305。在新的采区，工作面的长度是430m，同时，第一个480m宽的工作面目前正在开采。因此，所有的工作面，特别是最近的，都是超临界的，从而导致上覆岩层空隙的更彻底的垮落。研究区的一个广义的地层剖面图如图2所示。一个近3m厚的煤层组合在匹兹堡煤层上方的26m处。在这个区间，最后的煤层是位于匹兹堡煤层上方25m出的煤层。这两大煤层之间，有同等的稀少的煤和不连续的煤层，这是包含在采空区中的。气体排放与报告中采空区通风系统有关。在匹兹堡煤层上方的研究区砂岩河道通常代替页岩单元。河道的厚度变化在0-13m之间。Sewickley煤层可能分裂成两个独立的煤层，和上面的匹兹堡煤层高度不同。破碎带所含的气体，特别是Sewickley煤层中的气体，主要是采空区瓦斯通气孔的排放。图2匹兹堡煤层上方岩层剖面图2.2长臂采煤法网格模型为了模拟和分析长臂开采过程及相关的瓦斯控制系统，创建一个三维的矿山现场网格模型。网格模型的水平尺寸通常是根据问题的类型和面积来确定的。煤层位置的垂直层数和厚度是根据广义的地层剖面来确定。匹兹堡煤层的网格模型是根据几层不同的已开采或者未开采的长臂工作面及周围的条带数目来建立的。图3显示了这种建构的研究基地。图3匹兹堡煤层层位模型2.3采空区瓦斯通气孔和伪通风系统模型中采用了一个简化版的通风系统。在每一个工作面，通风系统的进气部分是一组速度在1700m³/min的压入式通风。抽风机是放在一个建立在大直径竖井的挡板侧的直径1.8m的风井之上，与井底造成的负压是1.36kPa。根据他们在相关位置确定了采空区瓦斯通气孔在模型中的位置，并根据他们实际完成的数据报告进行配置。端口通常打在匹兹堡煤层顶部12-13m处，并在61m的长管底部安有17.8cm的套管，如图1所示。然而，在某些情况下的通气孔，钻孔接近开采煤层及塌陷区，会影响他们的作用，这些将在下面的章