富(含)CO_(2)煤层气多源多阶成因研究进展及勘探开发启示

Research progress of multi-source and multi-stage genesis of CO_(2)-enriched CBM and the enlightenments for its exploration and development

富(含)CO_(2)煤层气承载着煤层气成因成藏的重要地质信息,与煤层气资源勘探及评价密切相关。在系统总结现阶段煤层气成因研究进展的基础上,通过解剖准噶尔盆地南缘富CO_(2)煤层气藏特殊地质范例,科学分析富(含)CO_(2)煤层气成因机制研究现状,全面梳理煤层气成因研究过程中存在的问题。结果表明,煤层气生成具有多源多阶段性,不同成因煤层气地球化学特征差异显著;现有煤层气成因判识图版及标准存在局限性,有必要建立煤层气成因多因素综合判识方法体系,结合区域地质条件及母质继承性差异,综合解释煤层气成因起源及伴生地质作用过程;富(含)CO_(2)煤层气藏含气构成、同位素组成及成藏过程,与早期煤化作用CO_(2)生成积聚、地下水参与下的CO_(2)差异溶解消耗、运移分馏、微生物后期改造等地球化学和生物地球化学作用息息相关;针对不同成因类型的煤层气藏应建立相应的资源评价指标体系,有效圈定甜点区与甜点层,对富含CO_(2)的煤层气藏需科学建立风氧化带深度界定标准,开展煤层气资源有效性评价。

CO_(2)-enriched coalbed methane(CBM) carries important geological information on CBM genesis and accumulation, and is closely related to the exploration and evaluation of CBM resources. On the basis of the systematic summary of the current research progress of CBM genesis, the current research status of the genetic mechanism of CO_(2)-enriched CBM reservoirs was scientifically analyzed by dissecting the special geological examples of CO_(2)-enriched CBM reservoirs in the southern Junggar Basin, and the problems in the research process of CBM genesis were comprehensively pointed out. The study shows that the generation of CBM has multiple sources and multiple stages, and different genesis of CBM significantly varies in geochemical characteristics. As there are limitations in the current CBM genesis identification charts and standards, it is necessary to establish a multi-factor comprehensive identification system of CBM genesis, and along with the regional geological conditions and parent material inheritance differences, the CBM genesis and the associated geological process are comprehensively explained. The gas composition, isotopic composition, and accumulation process of CO_(2)-enriched CBM reservoirs, are closely related to multiple geochemical and biogeochemical effects, including the generation and accumulation of CO_(2)in the early coalification, the differential dissolution and consumption of CO_(2)with the participation of groundwater, migration and fractionation, and the later transformation of microorganisms. For the different genesis of CBM reservoirs, the corresponding resource evaluation index system should be established to effectively delineate sweet spots and sweet formations. For CO_(2)-enriched CBM reservoirs, it is necessary to scientifically establish a standard for defining the depth of the aeolian oxidation zone and carry out the effective evaluation of CBM resources.