准噶尔盆地南缘部分地区低阶煤储层中CO2的富集，不仅反映了煤层气系统形成和改造过程受多元干预作用，也影响到煤层气资源的品质。为查明该区煤层中富CO2低阶煤层气藏形成机制，基于煤层气排采井气样，开展了煤层气地球化学研究。结果显示：准南地区煤层甲烷碳、氢同位素整体上偏轻，δ13C CH4为-6.82%～-4.38%，δ13D CH4为-29.00%～-30.41%；米泉地区煤层气以生物成因气为主，四工河及玛纳斯地区深部煤层主要发育热成因气，白杨河地区则以混合成因气为主；准南地区煤层气中CO2浓度差异大，多元地质因素干预明显，二氧化碳碳同位素偏重，δ13C CO2为-1.54%～2.51%，CO2来源主要为煤化作用初期热解和微生物成烃伴生。地下水动力条件是决定CO2富集的关键因素，煤化作用初期生烃阶段产生的CO2在滞流条件下聚集，微生物作用伴生CO2在弱径流条件下混入保存；煤层自燃致使烧变岩系发育，进而地表水下渗作用增强所引起的非烃类气体参与煤层气成藏，则符合真正意义上煤层气风氧化作用机制。综合研究认为，差异性地层水溶解消耗作用以及生物成烃改造作用主要影响煤层CO2的分布特征，煤层气成藏过程中存在的CO2干预作用形成了封闭滞流原位型、半封闭扰动型以及开放连通型三类煤层气藏，承载着煤层气成因、煤层气藏赋存特征等信息。

The low-rank coalbed methane（CBM）reservoirs in part of the southern Zhunggar Basin has higher CO2 enrichment degree,which not only reflects the multiple intervention in the process of formation and transformation of CBM system,but also affects the quality of CBM resources.To find out  mechanism on the formation of CO2-enriched coalbed methane reservoirs,geochemical research was carried out based on gas samples from production wells.The results indicate that the carbon isotope （δ13C CH4=-7.83%～-4.06%; δ13D CH4=-29.00%～-30.41%） of methane is generally lighter.The Miquan and Baiyanghe areas are dominated by biogenic gas and mixed causative gas,respectively,while the deep seams in Sigonghe and Manasi areas mainly developed thermally derived gas.There are significant vertical variations in CO2concentration,with obvious multiple geological factors intervention phenomena.Isotope analysis suggested that δ13C CO2 is generally heavier （δ13C CO2=-1.54%～2.51%）.The sources of CO2 are mainly from the pyrolysis at the beginning of coalification and microbial hydrocarbon generation.Hydrodynamic conditions played an important role in CO2 enrichment:the CO2 generated in the early hydrocarbon generation stage of coalification accumulates at stagnant condition.The associated CO2 of microbial action mixed and preserved under weak runoff conditions.The spontaneous combustion of coal seams leads to the development of burnt rocks and the enhanced underwater seepage,which resulted the participation of non-hydrocarbon gases in the formation of CBM.It is in line with the affected of CBM wind oxidation.Comprehensive analysis shows that the differential groundwater dissolution and bio-hydrocarbon reformation affected the distribution characteristics of CO2 in coal seams.CO2 intervention formed the closed-stagnant-in-situ,semi-closed perturbed,and open connected coalbed methane reservoirs,which carries key information such as the origin and the occurrence of coalbed methane resources.