柴达木盆地西部和北缘天然气中C_(5)—C_(7)轻烃地球化学特征  

Geochemical characteristics of C_(5)-C_(7)light hydrocarbons in natural gas from the western part and northern margin of the Qaidam Basin

作　　者：张臣 张道勇 周世新 李靖 陈克非 周立明 谷宇峰 ZHANG Chen;ZHANG Daoyong;ZHOU Shixin;LI Jing;CHEN Kefei;ZHOU Liming;GU Yufeng(Strategic Research Center of Oil and Gas Resources,Ministry of Natural Resources,Beijing 100034,China;Northwest Institute of Eco-Environment and Resources,Chinese Academy of Sciences/Key Laboratory of Petroleum ResourcesResearch,Gansu Province,Lanzhou 730000,China;PetroChina Research Institute of Petroleum Exploration&Development,Beijing)

机构地区：[1]自然资源部油气资源战略研究中心,北京100034 [2]中国科学院西北生态环境资源研究院/甘肃省油气资源研究重点实验室,甘肃兰州730000 [3]中国石油勘探开发研究院,北京100083

出　　处：《天然气地球科学》2024年第2期344-356,共13页Natural Gas Geoscience

基　　金：国家自然科学基金项目(编号:41872147,42272192,42302168);甘肃省油气资源研究重点实验室开放基金(编号:SZDKFJJ 2023/002)联合资助。

摘　　要：近些年在柴达木盆地西部和北缘油气勘探获得了新进展,但新勘探区块油气来源仍存在较大争议。C_(5)—C_(7)轻烃可作为很好的补充,为判识天然气来源提供新信息。系统采集了柴西和柴北缘主要油气田的天然气样品,分析其中轻烃的组分和单体烃碳同位素。结果显示:柴西天然气的轻烃具有高含量的正庚烷,柴北缘天然气的轻烃具有高含量的甲基环己烷和甲苯。柴西天然气中轻烃的δ^(13)C_(MCC5)值和δ^(13)C_(MCC6)值分别分布在-23‰~-18‰和-24‰~-20‰之间,柴北缘天然气中轻烃的δ^(13)C_(MCC5)值和δ^(13)C_(MCC6)值分别分布在-28‰~-22‰和-26‰~-23‰之间。这些特征反映出柴西地区天然气中轻烃主要来源于古近系—新近系咸水湖相泥岩,柴北缘地区天然气中轻烃主要来源于侏罗系煤系烃源岩。此外,结合天然气和原油地球化学特征,对南翼山和东坪地区油气来源开展了进一步研究。南翼山地区天然气可能有来自侏罗系和古近系—新近系煤系烃源岩的贡献,原油主要来自古近系—新近系烃源岩。东坪地区天然气主要来源于侏罗系煤系烃源岩,轻烃和凝析油主要来源于侏罗系泥岩。In recent years,oil and gas exploration have achieved progress in the western part and northern mar⁃gin of the the Qaidam Basin.But there is still a debate over the source of oil and gas in the new exploration ar⁃eas.C_(5)-C_(7)light hydrocarbons can be used to provide new information on the origin of natural gas.Natural gas samples were collected from the western part and northern margin of the Qaidam Basin.The components and in⁃dividual carbon isotopes of C_(5)-C_(7)light hydrocarbons in natural gas were analyzed.The results show that the light hydrocarbons from the western Qaidam Basin are characterized by a high content of n-heptane,and high carbon isotopes withδ^(13)C_(MCC5)andδ^(13)C_(MCC6)in the range from−23‰to−18‰and−24‰to−20‰,respectively.While light hydrocarbons from the northern margin of the Qaidam Basin are featured by high contents of methyl⁃cyclohexane and toluene,and relatively low carbon isotopes withδ^(13)C_(MCC5)andδ^(13)C_(MCC6)in the range from−28‰to−22‰and−26‰to−23‰,respectively.These characteristics indicate that the light hydrocarbons in the western Qaidam Basin mainly come from the saline lacustrine mudstones in the Paleogene-Neogene formation,and those in the northern Qaidam Basin are mainly generated from the Jurassic coal-bearing source rock.In addi⁃tion,combined with the geochemical characteristics of natural gas and crude oil,the sources of oil and gas in the Nanyishan and Dongping fields are further studied.In the Nanyishan oil and gas field,natural gas may come from the Jurassic coal-bearing source rocks and Paleogene-Neogene source rock,and crude oils are mainly pro⁃duced from Paleogene-Neogene source rock.In the Dongping gas field,natural gas is mainly generated from the Jurassic humic organic matters,while light hydrocarbons and condensate are mainly produced from the Jurassic sapropelic organic matters.

关 键 词：柴达木盆地 天然气 C_(5)-C_(7)轻烃 组分 碳同位素 

分 类 号：TE122.113[石油与天然气工程—油气勘探]