摘要
鄂尔多斯盆地东缘大宁–吉县地区二叠系山西组山_(2)^(3)亚段海陆过渡相页岩是未来非常规油气勘探的重点目标,通过野外露头观察、岩心描述、薄片鉴定,结合全岩衍射、特征微量元素测试等手段,划分出硅质页岩相、硅质黏土质页岩相、钙质硅质(或硅质钙质)页岩相、黏土质页岩相4种页岩岩相类型。岩石学特征、地球化学指标表明,山_(2)^(3)亚段继承了太原组沉积晚期地形平缓的陆表海格局,大规模海侵导致本区在山_(2)^(3)沉积早期快速演化为海湾环境,沉积环境由氧化转为还原,水体盐度接近正常海水,有机质保存有利,形成了该亚段下部富有机质页岩相,其中钙质硅质(或硅质钙质)页岩相是相对优质的富有机质页岩岩相,具有高有机质含量、高脆性矿物含量、低黏土含量的特点,为页岩气开发有利层段。进入山_(2)^(3)沉积晚期,区内逐渐演化为障壁岛沉积体系,在潟湖、滨岸沼泽环境中发育硅质黏土质页岩相、黏土质页岩相,虽多次受海侵影响,但海水影响程度总体上逐渐减弱,水体盐度呈降低趋势,沉积环境趋于氧化,有机质的保存条件变差,导致有机质含量总体偏低,同时脆性矿物含量偏少,不利于勘探开发。
The Shan_(2)^(3)Sub-member transitional facies shale of the Permian Shanxi Formation in the eastern margin of the Ordos Basin is a crucial target for future unconventional oil and gas exploration.Based on field outcrop observation,core description and thin-section identification,combined with X-ray diffraction,trace elements test and other analyses,four types of shale lithofacies were identified,including siliceous,siliceous-argillaceous,calcareous-siliceous(or siliceous-calcareous)and argillaceous lithofacies.The petrological characteristics and geochemical indicators show that the depositional environment of the Shan_(2)^(3)Sub-member inherited the epicontinental sea pattern with relatively gentle topography of the late Taiyuan Epoch.The large-scale transgression led to the rapid evolution of the study area into a bay environment in the early depositional stage of the Shan_(2)^(3)Sub-member.Thus,the sedimentary environment changed from oxidation to reduction.The salinity of the water body was close to normal seawater,and the preservation conditions for the organic matter were favorable,forming organic-rich shale lithofacies in the lower part of the Shan_(2)^(3)Sub-member.The calcareous-siliceous(or siliceous-calcareous)lithofacies are relatively high-quality organic-rich shale lithofacies with high TOC,brittle minerals,and low clay content;and are favorable for shale gas development.In the late depositional stage of the Shan_(2)^(3),the study area gradually evolved into a barrier island depositional system.Siliceous-argillaceous and argillaceous lithofacies developed in lagoon and coastal swamp environments.Though affected by multi-stage marine transgressions,seawater’s influence gradually weakened,water salinity decreased,the sedimentary environment tended to be oxidized,and organic matter preservation conditions worsened.
作者
孙越
蒋裕强
熊先钺
李星涛
李树新
邱振
孙雄伟
SUN Yue;JIANG Yuqiang;XIONG Xianyue;LI Xingtao;LI Shuxin;QIU Zhen;SUN Xiongwei(School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China;Unconventional Reservoir Evaluation Laboratory,PetroChina Key Laboratory of Unconventional Oil and Gas,Chengdu 610500,China;PetroChina Coalbed Methane Company Limited,Beijing 100028,China;PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China)
出处
《煤田地质与勘探》
CAS
CSCD
北大核心
2022年第9期104-114,共11页
Coal Geology & Exploration
基金
中国石油-西南石油大学创新联合体项目(2020CX030101)
国家自然科学基金项目(51674044)。
关键词
海陆过渡相页岩
岩相
沉积环境
地球化学指标
二叠系
山西组
鄂尔多斯盆地东缘
marine-continental transitional shale
lithofacies
sedimentary environment
geochemical indicator
Permian
Shanxi Formation
eastern Ordos Basin
