准噶尔盆地南缘(下称准南)蕴含着丰富的中-低煤阶煤层气资源，但勘探程度相对较低，气体成因和气藏形成机理认识不足，一定程度上制约了开发。为探究准南米泉地区中-低煤阶煤层气成因及其富集成藏机理，基于18口煤层气生产试验井的气样及其伴生的煤层产出水样，系统开展了相关样品的稳定同位素、水文地球化学以及放射性同位素定年等室内试验，综合运用经典的天然气识别图版等手段分析数据。结果显示大部分样品点落在图版“生物成因气”、“二氧化碳还原”、“微生物产甲烷伴生CO2”区域；水型表现为Na+·HCO-3·CI-型，煤层水矿化度较高；煤层水放射性同位素3H<1.0 TU及14C< 0.44%(现代碳百分数)。分析认为：准南米泉地区煤层气以生物成因为主，CO2还原为其主要的形成途径，该区异常高浓度CO2与微生物产甲烷活动密切相关。此外，米泉地区水动力场较为停滞，煤层水地质年龄较为古老，没有或较少现今地表水补给，该区现今水文地质条件不利于产甲烷菌生存及其产甲烷活动，现存的生物气资源应大多产生于较早地质历史时期。最后，综合区域构造与水文地质背景，结合古气候资料和煤层埋藏史等，研究提出米泉地区广泛发育封存性次生生物气藏，其形成分别经历了埋藏与成煤、抬升与剥蚀、地表水补给与生物气大量形成、产甲烷作用停止与水动力封存4个地质阶段。

The southern margin of Zhunnggar Basin contains rich resources of medium-low rank coalbed methane(CBM).However,the exploration degree is relatively low,and lack of understanding of gas genesis and gas reservoir formation mechanism restricts the development to a certain extent.In order to explore the genesis and accumulation mechanism of medium-low rank CBM in Miquan Area on the southern margin of Zhunnggar Basin,based on gas samples and associated coal seam water samples from 18 CBM production test wells,this study systematically carried out laboratory experiments of stable isotopes,hydro-geochemistry and radioisotope dating of relevant samples,and comprehensive use of the classical natural gas identification chart and other means to analyze the data.The results show that most of the samples are located in the regions of “biogenic gas”“CO2 reduction” and “CO2 associated with microbial methanogenesis”;the water type is Na+·HCO-3·CI-,and the TDS of coal seam water is high; the radioisotopes of coal seam water are 3H<1.0 TU and 14C< 0.44 pmC.The data analysis shows that CBM is mainly biogenic in Miquan Area and carbon dioxide reduction is the main way of its formation,the abnormally high CO2 concentration in this area is closely related to the activity of microbial methane production.In addition,the hydrodynamic field in Miquan Area is relatively stagnant,the geological age of coal seam water is relatively old,no or little current surface water supply,and the current hydrogeological conditions are not conducive to the survival of methanogens and their methanogenic activities,most of the existing biogas resources should have been produced in earlier geological history.Finally,combining the regional tectonic setting,hydrogeological condition,Paleo-climate data and coal seam burial history,it is proposed that sealed secondary biogenic gas reservoirs are widely developed in Miquan Area,its formation has experienced four geological stages:burial and coal formation,uplift and denudation,surface water supply and biogas formation,methane genesis stopping and hydrodynamic storage.