鄂尔多斯盆地靖边地区马家沟组中上组合天然气成因类型  

Genetic types of natural gas from upper&middle assemblage of Majiagou Formation in Jingbian area,Ordos Basin

作　　者：刘二虎 陈志鹏 王起琮 白宁 李晶 廖芸 LIU Erhu;CHEN Zhipeng;WANG Qicong;BAI Ning;LI Jing;LIAO Yun(The No.2 Gas Production Plant,Shaanxi Yanchang Petroleum(Group)Co.,Ltd.,Jingbian 718500,China;School of Earth Sciences and Engineering,Xi’an Shiyou University,Xi’an 710065,China)

机构地区：[1]陕西省延长石油(集团)有限责任公司延长气田采气二厂,陕西靖边718500 [2]西安石油大学地球科学与工程学院,陕西西安710065

出　　处：《西安科技大学学报》2022年第2期324-334,共11页Journal of Xi’an University of Science and Technology

基　　金：陕西省自然科学基础研究计划项目(2021JQ-592);陕西省教育厅科研计划项目(21JK0840)。

摘　　要：鄂尔多斯盆地靖边地区奥陶系马家沟组中上组合近年来相继取得重要油气发现,指示下古生界存在丰富的天然气资源。通过分析延长石油新钻井的古生界天然气组分、碳氢同位素以及流体包裹体等测试手段,分析靖边地区马家沟组中上组合天然气的组分、成因和分布特点,结合构造热演化历史,探讨天然气可能的主要来源。结果表明,马家沟组中上组合天然气自上而下总烃和重烃含量逐渐降低,非烃含量(CO_(2)、H_(2)S)和干燥系数逐渐增加。烷烃碳同位素组成呈现轻微的部分倒转,δ^(13)C_(CH 4)分布在-35.29‰~-34.15‰,δ^(13)C_(C_(2)H_(6))分布在-35.44‰~-33.46‰,δ^(13)C_(C_(3)H_(8))分布在-32.58‰~-30.22‰。马家沟组中上组合天然气整体上表现为油型气与煤成气混源的特征,且向下内幕气源岩的贡献不断增大。流体包裹体分析表明靖边地区马家沟组中上组合主要存在3期天然气充注,主力充注期烃源岩成熟度Ro在1.0%~1.3%,指示上古生界煤成气为主要来源,下古生界油型气也具有一定贡献。Numerous hydrocarbons have been discovered from the upper and middle assemblage of Majiagou Formation of Ordovician in the Central-Western Ordos Basin recently,which indicates that there are plentiful natural gas resources in the Lower Paleozoic.Composition,genesis and distribution characteristics of natural gas in the middle and upper Majiagou Formation in Jingbian area are analyzed based on natural gas components,carbon and hydrogen isotopes of alkanes,and fluid inclusions.Combined with the tectonic-thermal evolution history of Jingbian area,the sources of nature gas are explored.The results show that the contents of total hydrocarbon and heavy hydrocarbon decrease gradually from top to bottom,while the contents of non-hydrocarbon(CO_(2),H_(2)S)and dry coefficient increase gradually.The nature gas from the upper and middle assemblage of Majiagou Formation of Ordovician is characterized by a slight partial carbon isotopes reversal,with theδ^(13)C_(CH 4) ranging from-35.29‰to-34.15‰,theδ^(13)C_(C_(2)H_(6)) ranging from-35.44‰to-33.46‰,theδ^(13)C_(C_(3)H_(8)) ranging from-32.58‰to-30.22‰.It indicates that the natural gas of Majiagou Formation in Jingbian area is mixed by the coal-derived gases and oil formed gas,and the contribution of the lower source rocks is increasing with the depth.The analysis of fluid inclusions shows that there are mainly three stages of natural gas charging in the upper and middle assemblages of the Majiagou Formation in Jingbian area.The source rock maturity Ro corresponding to the main charging period is between 1.0%and 1.3%,indicating that the Upper Paleozoic coal-derived gas is the main source.Lower Paleozoic oil-type gas also has a certain contribution.

关 键 词：天然气成因 流体包裹体 马家沟组 鄂尔多斯盆地 

分 类 号：TE121[石油与天然气工程—油气勘探]