煤层气直井压裂效果及其对产能影响——以窑街矿区为例_马代兵.pdf

煤层气直井压裂效果及其对产能影响以窑街矿区为例马代兵1，陈立超2（1.甘肃煤田地质局一四九队,甘肃兰州730020；2.煤与煤层气共采国家重点实验室,山西晋城048204）摘要：煤层气藏作为典型缝控气藏，压裂造缝规模及裂缝充填效果对气井产能具有决定性控制。为探究煤层气直井水力压裂效果对气井产能效果的影响机制，以甘肃窑街海石湾矿区为例，重点报道直井开发形式下煤储层压裂改造效果及其对产能制约方面认识，结果表明：煤层气井破裂压力主要反馈井筒固井水泥环特征而非煤储层力学性能，从该井压裂曲线看破裂压力不明显，表明井筒环空固井水泥环厚度适中，水力压裂期间固井水泥环破裂相对容易，能量消耗低，注入压裂液能量主要用于撑开煤岩裂缝；从压裂曲线看出，该井压裂裂缝延伸压力较高，表明地下煤储层结构较为破碎且发育煤粉源集合体，煤粉对压裂裂缝的延展具有关键制约作用。而且在压裂曲线裂缝延展阶段出现多个波动形态特征，指示多条次级裂缝撑开，整体上该井压裂裂缝形态较为复杂，推测为主干压裂裂缝两侧发育枝状次级裂缝形式；该井注砂后发生严重砂堵，主要原因是煤储层压裂液滤失造成近井地带压裂裂缝内支撑剂脱砂形成楔体，导致后续支撑剂注入困难，同时也与煤储层原生裂缝煤粉源及少量构造煤粉源集合体发育有关；压裂微震监测数据显示该井煤储层主干压裂裂缝走向为 NE50，其中在北东方向上煤岩微震事件更活跃，指示该方向上煤储层天然裂隙系统更发育；结合煤储层压裂裂缝矿井观测结果，提出压裂裂缝有效支撑区、实际破裂区及岩体扰动区的划分方案，认为微震监测得出的压裂裂缝半长实际为岩体扰动范围，难以准确反映储层实际改造效果。综合该井后期产能规律及晋城矿区煤储层压裂裂缝矿井观测结果，认为该井煤储层实际压裂裂缝半长在 20m 以内，有效支撑压裂裂缝半长不足 5m，压裂液注入液量少、压裂液滤失诱导支撑剂脱砂形成楔体以及煤粉聚集造成砂堵等是该井煤储层压裂裂缝较短的主要因素；结合煤层气产能规律，认为该井气藏管控和排采制度较为合理，但煤储层有效支撑压裂裂缝过短，煤储层内煤粉运移导致近井压裂裂缝导流能力快速衰减是气井产能低下的关键制约机制，建议后期煤储层水力压裂加大压裂液注入液量，适当增大压裂液排量，降低支撑剂砂比，重点防控压裂液滤失、防止脱砂楔体形成。该区煤储层埋深大、应力高，实现裂缝大范围加砂是煤储层压裂改造的关键。同时考虑储层干燥，压裂液滤失严重的实际情况，有条件可开展 CO2前置压裂试验。关键词：煤层气直井；压裂效果；天然裂隙系统；压裂液滤失；甘肃窑街矿区中图分类号：TD712;P618文献标志码：A文章编号：02532336（2023）06013007Hydraulic fracturing effect of CBM vertical well and its impact on productivity:a case study of Yaojie Mining AreaMADaibing1,CHENLichao2收稿日期：20220510责任编辑：常琛DOI：10.13199/ki.cst.2022-0539基金项目：山西省煤层气联合研究基金资助项目(2016012007)作者简介：马代兵（1969），男，甘肃天水人，高级工程师。E-mail:通讯作者：陈立超（1985），男，内蒙古赤峰人，副教授，博士。E-mail:第51卷第6期煤炭科学技术Vol.51No.62023年6月CoalScienceandTechnologyJun.2023地球科学与测绘马代兵，陈立超.煤层气直井压裂效果及其对产能影响以窑街矿区为例J.煤炭科学技术，2023，51（6）：130136.MADaibing，CHENLichao.HydraulicfracturingeffectofCBMverticalwellanditsimpactonproductivity:acasestudyofYaojieMiningAreaJ.CoalScienceandTechnology，2023，51（6）：130136.130（1.149th Team,Gansu Coal Geology Bureau,Lanzhou 730020,China;2.State Key Laboratory of Coal and CBM Co-mining,Jincheng 048204,China）Abstract:CBMreservoirisatypicalfracture-controlledgasreservoir,andthescaleoffracturingandfracture-fillingeffecthavedecisivecontrolongaswellproductivity.InordertorevealtheinfluencemechanismofthehydraulicfracturingeffectofCBMverticalwellsontheproductivityeffectofgaswells,takingtheHaishiwanMiningAreaofYaojie,Gansuasanexample,thispaperfocusesonreportingthefracturingeffectofcoalreservoirsundertheformofverticalwelldevelopmentanditsunderstandingoftheconstraintsonproductivity.theresultshows:ThefracturepressureofCBMwellmainlyfeedsbackthecharacteristicsofthewellborecementsheathratherthanthemechanicalpropertiesofthecoalreservoir.Fromthefracturingcurveofthiswell,thefracturepressureisnotobvious,indicatingthatthethicknessofthecementsheathinthewellboreannulusismoderate,andthecementsheathisrelativelyeasytoruptureduringhydraulicfracturing.Theenergyoftheinjectedfracturingfluidismainlyusedtopropupthecoalcracks;Itcanbeseenfromthefracturingcurvethatthepropagationpressureofthehydraulicfractures(HF)inthiswellisrelativelyhigh,indicatingthatthestructureofcoalreservoirisrelativelyfragmentedandcoalfinesaredeveloped.Inaddition,therearemultiplewavemorphologicalfeaturesinthefracturepropagationstageofthefracturingcurve,indicatingthatmultiplesecondaryfracturesareproppedup.Onthewhole,theHFinthiswellarerelativelycomplex,anditisspeculatedthatbranchedsecondaryfracturesdeveloponbothsidesofthemainHF.Serioussandpluggingoccurredaftersandinjectioninthiswell.Themainreasonwasthatthefracturingfluidinthecoalreservoirwaslostduetothelossofthefracturingfluidinthenear-wellborearea,resultingintheformationofwedgesbyproppantde-sandingintheHF,whichmadesubsequentproppantinjectiondifficult.Itisrelatedtothecoalfinesofprimaryfracturesandthedevelopmentofasmallamountoftectoniccoalfines;ThefracturingmicroseismicmonitoringdatashowthatthemainHFofthecoalreservoirinthiswellareNE50,andthecoalrockmicroseis-miceventsaremoreactiveinthenortheastdirection,indicatingthatthenaturalfracture(NF)ofthecoalreservoirismoredevelopedinthisdirection;Basedontheobservationresultsoffracturingandmineback,thispaperproposesadivisionplanfortheeffectiveproppedarea,theactualfractureareaandtherockmassdisturbanceareaofHF.Itisbelievedthattheactualhalf-lengthoftheHFinthecoalreservoirofthiswellislessthan20m,thehalf-lengthoftheeffectivelyproppedHFislessthan5m,andThesmallamountoffracturingfluidinjected,theformationofwedgesbyproppantde-sandinginducedbyfracturingfluid-loss,andthesandpluggingcausedbycoalfinesaccumulationarethemainfactorsfortheshortfracturesinthecoalreservoirofthiswell;Combinedwiththelawofcoalbedmethaneproductivity,itisconsideredthatthegasreservoirmanagementanddrainagesysteminthiswellisreasonable,However,theeffectiveproppedHFinthecoalreservoiraretooshort,andthecoalfinesmigrationinthecoalreservoirleadstotherapiddeclineoftheconductivityofthenear-wellHF,whichisthekeyrestrictingmechanismfortheproductivityofgaswells.Itisrecommendedtoincreasetheinjectionvolumeoffractur-ingfluid,appropriatelyincreasetheflowrateoffracturingfluid,reducetheproppant-sandratio,andfocusoncontrollingfracturingfluidleak-offandtheformationofscreenoutwedgesinthehydraulicfracturingofcoalreservoirsinthelaterstage.Thecoalseaminthisareahas