下扬子地区寒武系页岩气成藏条件分析与资源潜力评价
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摘要
下扬子地区寒武系为海相沉积地层,分布面积达13×10~4 km~2,其中下寒武统荷塘组(幕府山组)发育黑色碳质泥岩,厚度达276 m,有机碳含量为0.25%～23.52%,平均含量为4.54%,有机质类型以Ⅰ型为主,页岩气成藏条件十分有利。该区下寒武统地层经历了加里东、华力西、印支、燕山和喜马拉雅期的构造运动及岩浆活动的改造,个别地段已经成为变质岩的一部分;很多地区荷塘组碳质泥岩演化程度较高,镜质体反射率(R_o)最大可达6.32%,完全处于过成熟阶段。该区荷塘组上覆地层较厚,但受构造影响,荷塘组地层埋藏深度变化较大。综合荷塘组碳质泥岩的厚度、埋深、有机碳含量和镜质体反射率等4个方面的指标,开展了下扬子地区寒武系地层的页岩气地质调查和潜力评价,共划分出3个页岩气远景目标区,分布于江西上饶—浙江桐庐、江苏扬州和安徽全椒等地,估算资源量为288 944.4×10~8 m~3。
The Cambrian in the Lower Yangtze region is a marine sedimentary stratum with an area of 130×10~3km~2. The Lower Cambrian Hetang Formation(Makufushan Formation) comprisesblack carbonaceous mudstones with a thickness of 276 m and an organic carbon content(TOC) rangingfrom 0.25%-23.52%, averaging 4.54%. The organic matter is mainly of type I, showing favorable conditions for shale gas accumulation. The Lower Cambrian stratum has experienced tectonic movements and transformation duringmagmatic activityduring the Caledonian, Hercynian, Indosinian, Yanshanian and Himalayan periods, and some individual sections have become part of metamorphic rocks. Therefore, the thermal evolution degree of carbonaceous mudstones is high in the Hetang Formation in many areas of the Lower Yangtze region. The maximum vitrinite reflectance(R_o) is 6.32%, indicating for an over mature stage. At the same time, due to large overburden and structural influence, the burial depth of the Hetang Formation also varies. The thickness, burial depth, TOC content and Ro of the carbonaceous mudstones in the Hetang Formation were applied to construct ageological survey and potential evaluation of shale gas in the Cambrian in the Lower Yangtze region. There are mainly three exploration targets including the region from the Shangrao area in the Jiangxi Province to the Tonglu area in the Zhejiang Province, the Yangzhou area in the Jiangsu Province and the Quanjiao area in the Anhui Province, with an estimated resource of 28894×10~9m~3.
The Cambrian in the Lower Yangtze region is a marine sedimentary stratum with an area of 130×10~3km~2. The Lower Cambrian Hetang Formation(Makufushan Formation) comprisesblack carbonaceous mudstones with a thickness of 276 m and an organic carbon content(TOC) rangingfrom 0.25%-23.52%, averaging 4.54%. The organic matter is mainly of type I, showing favorable conditions for shale gas accumulation. The Lower Cambrian stratum has experienced tectonic movements and transformation duringmagmatic activityduring the Caledonian, Hercynian, Indosinian, Yanshanian and Himalayan periods, and some individual sections have become part of metamorphic rocks. Therefore, the thermal evolution degree of carbonaceous mudstones is high in the Hetang Formation in many areas of the Lower Yangtze region. The maximum vitrinite reflectance(R_o) is 6.32%, indicating for an over mature stage. At the same time, due to large overburden and structural influence, the burial depth of the Hetang Formation also varies. The thickness, burial depth, TOC content and Ro of the carbonaceous mudstones in the Hetang Formation were applied to construct ageological survey and potential evaluation of shale gas in the Cambrian in the Lower Yangtze region. There are mainly three exploration targets including the region from the Shangrao area in the Jiangxi Province to the Tonglu area in the Zhejiang Province, the Yangzhou area in the Jiangsu Province and the Quanjiao area in the Anhui Province, with an estimated resource of 28894×10~9m~3.
引文
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[4] 袁勇,陈建文,梁杰,等.海陆对比看南黄海海相中-古生界的生储盖组合特征[J].石油实验地质,2017,39(2):195-202. YUAN Yong,CHEN Jianwen,LIANG Jie,et al.Source-reservoir-seal assemblage of marine Mesozoic-Paleozoic in South Yellow Sea Basin by land-ocean comparison[J].Petroleum Geology & Experiment,2017,39(2):195-202.
[5] 赵立鹏,王冉,钟方军,等.赣东北重点泥页岩层系地球化学特征分析[J].特种油气藏,2017,24(1):64-69. ZHAO Lipeng,WANG Ran,ZHONG Fangjun,et al.Geochemistry features of key mud shale formations in Northeast Jiangxi Province[J].Special Oil & Gas Reservoirs,2017,24(1):64-69.
[6] 曹涛涛,邓模,罗厚勇,等.下扬子地区中上二叠统页岩有机孔发育特征[J].石油实验地质,2018,40(3):315-322. CAO Taotao,DENG Mo,LUO Houyong,et al.Characteristics of organic pores in Middle and Upper Permian shale in the Lower Yangtze region[J].Petroleum Geology & Experiment,2018,40(3):315-322.
[7] 安徽省地质矿产局区域地质调查队.安徽地层志:前寒武系分册[M].合肥:安徽科学技术出版社,1985. Regional Geological Survey Team of Anhui Provincial Bureau of Geology and Mineral Resources.Stratigraphic records of Cambrian in Anhui[M].Hefei:Anhui Science and Technology Press,1985.
[8] 张飞燕.下扬子地区下寒武统页岩特征及有利勘探方向探讨[J].中国煤炭地质,2017,29(1):25-30. ZHANG Feiyan.Discussion on Lower Cambrian shale features and favorable exploration orientation in Lower Yangtze area[J].Coal Geology of China,2017,29(1):25-30.
[9] 吴浩.安徽省扬子地层区古生界页岩气地质条件与勘探前景[D].南京:南京大学,2014. WU Hao.The Paleozoic shale gas geological condition and prospect in Yangzi stratum area,Anhui Province[D].Nanjing:Nanjing University,2014.
[10] 刘小平,潘继平,刘东鹰,等.苏北地区下寒武统幕府山组页岩气勘探前景[J].成都理工大学学报(自然科学版),2012,39(2):198-205. LIU Xiaoping,PAN Jiping,LIU Dongying,et al.Shale-gas exploration prospect of Lower Cambrian Mufushan Formation in the northern Jiangsu,China[J].Journal of Chengdu University of Technology(Science & Technology Edition),2012,39(2):198-205. (编辑