黑色页岩氧化还原条件与有机质富集机制——以昭通页岩气示范区A井五峰组-龙马溪组下段为例

doi:10.11743/ogg20170512

摘要/Abstract

摘要： 五峰组-龙马溪组下段为昭通示范区页岩气勘探开发的主要目的层段，基于A井样品有机碳、微量元素及稀土元素的系统测试，结合岩石学及测井资料，系统分析A井黑色页岩相关元素地球化学参数的变化特征，揭示黑色页岩形成的氧化还原条件，探讨有机质富集机制。研究结果表明：昭通页岩气示范区五峰组-龙马溪组下段Ⅰ亚段TOC含量最高，平均为3.13%，向上含量逐渐降低，且相关元素富集程度与TOC含量相关。微量元素及稀土元素等氧化还原参数指示：五峰组-龙马溪组下段，纵向上水体整体由厌氧还原环境向次氧化环境过渡，Ⅰ亚段为贫氧-厌氧环境，Ⅱ亚段为贫氧环境，Ⅲ亚段为贫氧-富氧环境。其中，Ⅰ-1小层、Ⅰ-3及Ⅰ-4小层水体还原性强于Ⅰ-2小层与I-5小层。在高古生产力背景下，五峰组与龙马溪组黑色页岩有机质富集的氧化还原环境形成机制存在差异。五峰组为水体滞留形成厌氧-贫氧环境使有机质有效保存，龙马溪组底部则主要由于海平面上升形成厌氧环境而使有机质有效保存富集。五峰组-龙马溪组下段I亚段有机质最为富集，为页岩气开发的最优层段。

关键词: 氧化还原条件, 有机质富集, 微量元素, 稀土元素, 页岩气, 黑色页岩

Abstract: The Wufeng-lower Longmaxi Formations are the main exploration targets of the Zhaotong shale gas demonstration area.Based on systematic tests of organic carbon,trace elements and REE (rare earth elements) upon samples from Well A in the area,as well as petrological and logging data,we analyzed the variations of geochemical parameters of relevant elements in black shale samples from Well A and tried to reveal the redox conditions of black shale and discuss the possible mechanisms of organic matter enrichment in the area.The results show that the sub-member I of the Wufeng-lower Longmaxi Formations in the area have the highest content of TOC,which is averaged at 3.13% and displays an upward decreasing trend.The enrichment of relevant elements is also observed to be connected with TOC content.Redox parameters such as trace elements and REE indicate that the Wufeng-lower Longmaxi Formations had once experienced anaerobic redox water body turning to a suboxidizing water body with the sub-member I in an anoxic-anaerobic environment,the sub-member Ⅱ in an anoxic environment and the sub-member Ⅲ in an anoxic -oxygen enriched environment.Among them the water body reducibility of layers I-1,I-3,and I-4,is stronger than that of layers I-2 and I-5.And there were still disparities in the forming mechanisms of redox environment for organic matter enrichment in black shale of the Wufeng and Longmaxi Formations against a high paleo-productivity in the area.For the Wufeng Formation,it was a stagnant water body that preserved the organic matter in an anaerobic-anoxic environment,and for the lower Longmaxi Formation,it was sea level rising that kept a rich organic matter in an anaerobic environment.The sub-member I at the Wufeng-lower Longmaxi Formations has the richest TOC and thus is regarded as the best target for shale gas development.

Key words: redox condition, organic matter enrichment, trace element, rare earth element, shale gas, black shale

中图分类号:

TE121.1

王鹏万,张磊,李昌,等. 黑色页岩氧化还原条件与有机质富集机制——以昭通页岩气示范区A井五峰组-龙马溪组下段为例[J]. 石油与天然气地质, 2017, 38(5): 933-943. doi: 10.11743/ogg20170512 Wang Pengwan,Zhang Lei,Li Chang,et al. Redox conditions and organic enrichment mechanisms of black shale:A case from the Wufeng-lower Longmaxi Formations in Well A in Zhaotong shale gas demonstration area[J]. Oil & Gas Geology, 2017, 38(5): 933-943. doi: 10.11743/ogg20170512

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