威宁地区下石炭统祥摆组:一个潜在的薄互层煤系气新层系  

Lower Carboniferous Xiangbai Formation in Weining area:A potential new formation of thin interbedded coal measures gas

作　　者：金军[1,2] 秦勇[1,2] 易同生 高为[2] 颜智华[2] 李耿 JIN Jun;QIN Yong;YI Tongsheng;GAO Wei;YAN Zhihua;LI Geng(Key Laboratory of CBM Resources and Reservoiring Process,China University of Mining and Technology,Xuzhou,Jiangsu,221008;Coal Geology Bureau of Guizhou,Guiyang,550081)

机构地区：[1]中国矿业大学煤层气资源与成藏过程教育部重点实验室,江苏徐州221008 [2]贵州省煤田地质局,贵阳550081

出　　处：《地质论评》2023年第5期1879-1891,共13页Geological Review

基　　金：国家自然科学基金重点资助项目(编号:42130802);贵州省地质勘查基金重点资助项目(编号:黔财建[2019]1号)的成果。

摘　　要：水页1井未压裂煤系高产气流的偶然发现,昭示黔西北威宁及其邻区下石炭统祥摆组可能成为我国西南局部地区煤系气勘查新层系。然而,该区祥摆组前期煤系气地质调查有限,关于资源条件和前景区的认识存在一定差异,且对煤系特点考虑不足。鉴于此,基于近期地质调查进展,结合前人基础地质研究成果,探讨了威宁及其邻区祥摆组煤系气地质条件和勘查前景。结果显示,威宁地区祥摆组是一套典型的薄互层煤系,下段潮坪—潟湖相煤系气显示强烈,但煤系储层总体上具有低孔特低渗的特征。单井研究发现,随埋深加大,祥摆组储层吸附气含量存在一个“临界深度”,一旦超过该深度,煤系页岩吸附甲烷含量快速增高,煤层吸附甲烷含量开始降低但其游离气含量可能增大,导致总含气量可能明显增大。综合分析认为,威宁地区祥摆组在埋深大于1500 m之后可能具有综合开发价值,龙街、羊场、海改地、二都、天星洞、玉龙6个深向斜是下一步勘查的重点构造单元,往东可扩展到黔西地区格目底、晴隆、朗岱等较大规模深向斜构造。同时,逆冲推覆构造对祥摆组煤系气保存条件的影响值得高度关注。基于上述分析,提出了落实祥摆组煤系气勘查战略选区的5条原则性建议。Objectives:The accidental discovery of high-production gas flow from the unfractured coal measures in well Shuiye 1 shows that the Lower Carboniferous Xiangbai Formation in Weining and its adjacent areas in northwest Guizhou may become a new formation of coal measures gas(CMG)exploration in some areas of the Southwest China.However,the previous geological survey of CMG for the formation in this area is insufficient,there are some differences in the understanding of CMG resources and the prospect spots,and the characteristics of CMG are not considered enough.Methods:In view of this,based on the recent geological survey and the previous basic geological research,the geological conditions and exploration prospect of CMG gas in the Xiangbai Formation in Weining and its adjacent areas are discussed.Results:The results show that the Xiangbai formation in Weining area is a typical set of thin-interbedded coal measures,and has strong CMG display in the lower member of the formation formed in tidal flat and lagoon facies,but the coal measures reservoirs are generally characterized by low porosity and low permeability.It is found that with the increase of buried depth,there is a“critical depth”for the adsorbed gas volume of the reservoirs.Once exceeding this depth,the adsorbed methane volume of coal measures shale rapidly increases,and that of coal seams begins to reduce,but its free gas volume in coal seams may increase,resulting in a significant increase in total gas volume.Conclusions:Based on the comprehensive analysis,it is suggested that the Xiangbiao Formation in Weining area may have the value of comprehensive CMG development when the burial depth is more than 1500 m.Six deep synclines,including the Longjie,Yangchang,Haigaidi,Erdu,Tianxingdong and Yulong ones,are the key structural units for further CMG exploration in Xiangbai formation,and the exploration prospect could be extended to some deep synclines in the east,such as Gemudi,Qinglong and Langdai ones.At the same time,the influence of thrust nappe structu

关 键 词：下石炭统祥摆组 薄互层 煤系气 保存条件 战略选区 黔西北 

分 类 号：P618.13[天文地球—矿床学]