鄂尔多斯盆地三叠系长7段黑色页岩形成环境及其对页岩油富集段的控制作用  

Black shale formation environment and its control on shale oil enrichment in Triassic Chang 7 Member,Ordos Basin,NW China

作　　者：张斌[1] 毛治国[1] 张忠义[2] 袁懿琳[1] 陈小亮 石雨昕 刘广林[2] 邵晓州[2] ZHANG Bin;MAO Zhiguo;ZHANG Zhongyi;YUAN Yilin;CHEN Xiaoliang;SHI Yuxin;LIU Guanglin;SHAO Xiaozhou(Research Institute of Petroleum Exploration and Development,PetroChina,Beijing 100083,China;Institute of Petroleum Exploration and Development of Changqing Oilfield Company,PetroChina,Xi’an 710021,China;China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]中国石油长庆油田公司勘探开发研究院,西安710021 [3]中国地质大学(北京),北京100083

出　　处：《石油勘探与开发》2021年第6期1127-1136,共10页Petroleum Exploration and Development

基　　金：国家科技重大专项(2016ZX05050);中国石油勘探开发研究院科学研究与技术开发项目(2018ycq02)。

摘　　要：基于鄂尔多斯盆地西北缘钻探的三叠系延长组7段全取心井冯75井的地球化学分析,结合区域地质特征,对黑色页岩形成环境及其对页岩油富集的控制作用进行综合研究。自长73亚段到长71亚段黑色页岩中的有机碳含量从5.70%降至3.55%,氢指数从345 mg/g降至269 mg/g,而氧指数从6 mg/g逐渐增高至29 mg/g,指示长72亚段和长73亚段沉积时期为严重缺氧环境。生物标志化合物出现规律性变化,在长73亚段深度为2753~2777 m的井段出现明显“拐点”,指示陆源有机质输入增多。但是,在“拐点”附近出现有机碳同位素组成负向漂移,偏差约为2%,与生物标志化合物结果矛盾。古秦岭地区陆上火山活动所引起的极热和缺氧事件是造成其邻近的鄂尔多斯盆地黑色页岩中有机碳同位素组成负向漂移的主要原因。火山活动导致气温升高,空气污浊,引发极端天气,洪水增多,陆源有机质输入增多,同时形成极度缺氧环境,有利于有机质保存。陆源有机质比水生有机质更有利于形成轻质油,是页岩油富集的重要“甜点”层段。Based on geochemical analysis results of core samples from the Triassic Chang 7 Member of Well Feng 75 drilled in the northwest margin of Ordos Basin,combined with geological characteristics of this region,the formation environment of the black shale and its control on shale oil enrichment are comprehensively studied.From Chang 73 to Chang 71 sub-members,the black shales have organic carbon contents decreasing from 5.70%to 3.55%,hydrogen indexes decreasing from 345 mg/g to 269 mg/g,while the oxygen indexes increasing gradually from 6 mg/g to 29 mg/g,indicating that the sedimentary environment during the depositional period of Chang 72 and Chang 73 sub-members was anoxic.Biomarkers in the black shales change regularly,and have an obvious“inflection point”at the depth of 2753–2777 m in Chang 73 sub-member,indicating that the input of terrigenous organic matter increased.However,there is a negative drift about 2%of organic carbon isotopic composition near the“inflection point”,which is in conflict with the results of biomarker compounds.This is because the extreme thermal and anoxic events caused by continental volcanic activity in the ancient Qinling region caused negative drift of carbon isotopic composition of the black shale in the Ordos Basin.The volcanic activity caused rise of temperature,polluted air,extreme weathers,more floods and thus more input of terrigenous organic matter,and gave rise to extremely anoxic environment conducive to the preservation of organic matter.Terrigenous organic matter is more conducive to the formation of light oil than aquatic organic matter,so these sections in Yanchang Formation are major“sweet spots”for shale oil enrichment.

关 键 词：黑色页岩 三叠系 沉积环境 火山灰 缺氧事件 页岩油 鄂尔多斯盆地 长7段 

分 类 号：TE122.1[石油与天然气工程—油气勘探]