二连盆地巴彦花凹陷煤层气成因类型及生气潜力  

Genetic type and gas-generating potential of coalbed methane in the Bayanhua Sag,Erlian Basin

作　　者：孟芹 李玲 李杰 田文广[3] 林海涛 李恒 MENG Qin;LI Ling;LI Jie;TIAN Wenguang;LIN Haitao;LI Heng(Inner Mongolia Coal Exploration Unconventional Energy Co.,Ltd.,Hohhot 010010,China;Inner Mongolia Coal Exploration&New Energy Development Co.,Ltd.,Hohhot 010010,China;PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China)

机构地区：[1]内蒙古煤勘非常规能源有限责任公司,内蒙古呼和浩特010010 [2]内蒙古煤勘新能源开发有限公司,内蒙古呼和浩特010010 [3]中国石油勘探开发研究院,北京100083

出　　处：《煤田地质与勘探》2023年第11期24-33,共10页Coal Geology & Exploration

基　　金：中国石油天然气股份有限公司“十四五”重大科技项目(2021DJ2303);中央引导地方科技发展资金项目(2022ZY0018)。

摘　　要：二连盆地巴彦花凹陷是内蒙古低阶煤煤层气重点开发试验区,但勘探程度相对较低,对煤层气成因认识不足,在一定程度制约了勘探开发进度。通过对巴彦花凹陷煤层气井气样水样开展气体组分、稳定同位素、水化学及放射性同位素定年等测试,并结合经典天然气成因判识图版厘清气体成因,进一步剖析生气潜力,明确生气关键要素。结果显示:C_(1)/C_(1)—5>0.99,CO_(2)-CH_(4)系数[CDMI=φ(CO_(2))/φ(CO_(2)+CH_(4))×100%]基本小于5%,干燥系数(C_(1)/C_(2+))介于104~5540,CH_(4)含量高、重烃及CO_(2)含量低。δ^(13)C(CH_(4))介于-51.80‰~-67.70‰、δD(CH_(4))介于-226.20‰~-291.00‰,δ^(13)C(CO_(2))介于-20.30‰~-37.60‰,为陆相生物成因气特征;判识图版中大部分煤层气样品落在生物成因气区域,甲烷产气途径为乙酸发酵和甲基发酵,CO_(2)主要是微生物产甲烷活动伴生产物。煤层水来源于大气降水,主要为NaHCO_(3)型弱碱性水,δ^(13)C_(DIC)为-2.6‰,δ^(18)O(H_(2)O)为-16.4‰,结合14C定年表明水为第四纪水,非原生水,为现代混合水。结合全区构造和水文地质条件分析认为,巴彦花凹陷径流区利于乙酸发酵产气,弱径流区利于生物气富集成藏。区内低阶煤储层孔渗性较好,地温适宜,水文地质条件优越,利于生物气的生成,承压区水力封堵型生物气藏发育。水文地质条件是本区生物气形成关键,在煤层气勘探选区中应重点关注。The Bayanhua Sag in the Erlian Basin is a critical experimental area for coalbed methane(CBM)development from low-rank coals in Inner Mongolia.However,the relatively low exploration level and the limited understanding of the CBM origin in the sag restrict the CBM exploration and development to some extent.This study tested the gas components,stable isotopes and hydrochemistry of the gas and water samples from CBM wells in the Bayanhua Sag.It also conducted radioisotopic dating for these samples.By combining the classic charts for the identification of natural gas origin,this study clarified the gas origins,further analyzed the gas-generating potential,and identified the critical gasgenerating factors.The results show that the CBM from the sage is characterized by C_(1)/C_(1)-5 ratios greater than 0.99,CO_(2)-CH_(4)coefficient[CDMI=φ(CO_(2))/φ(CO_(2)+CH_(4))×100%]roughly less than 5%,drying coefficient(C_(1)/C_(2+))between 104‒5540,high CH_(4)contents,and low heavy hydrocarbon and CO_(2)contents.Furthermore,theδ^(13)C(CH_(4)),δD(CH_(4)),andδ^(13)C(CO_(2))values of the CBM range from−51.80‰to−67.70‰,from−226.20‰to−291.00‰,and from−20.30‰to−37.60‰,respectively,suggesting the characteristics of continental biogenic gas.In the identification charts,the CBM samples mostly fell within the biogenic gas zone,indicating that methane originated from acetic-acid and methyl fermentation and that CO_(2)is primarily the associated product of microbial methanogenesis.Coalbed water,originating from meteoric water,is NaHCO_(3)type of slightly alkaline water primarily,withδ^(13)C_(DIC) andδ^(18)O(H_(2)O)values of−2.6‰and−16.4‰,respectively.Based on these findings,as well as the 14C dating results,the coalbed water is inferred to be the Quaternary water and modern mixed water rather than primary water.By combining the analysis of the structures and hydrogeological conditions in the Bayanhua Sag,it can be concluded that the runoff areas in the sag are favorable for gas production from acetic

关 键 词：二连盆地 巴彦花凹陷 低阶煤 煤层气 成因类型 生气潜力 

分 类 号：P618.13[天文地球—矿床学]