准噶尔盆地北部石北凹陷天然气地球化学特征及成因  

Geochemical characteristics and origin of natural gas in Shibei Sag,northern Junggar Basin

作　　者：李园园 曲彦胜 王圣柱[1] 熊峥嵘 吕铁良[1] LI Yuanyuan;QU Yansheng;WANG Shengzhu;XIONG Zhengrong;LÜTieliang

机构地区：[1]中国石化胜利油田勘探开发研究院

出　　处：《海相油气地质》2023年第2期178-185,共8页Marine Origin Petroleum Geology

基　　金：国家科技重大专项课题“准噶尔盆地碎屑岩层系油气富集规律与勘探评价”(编号:2016ZX05002-002);中国石化科技攻关项目“石炭系领域油气成藏规律及目标评价”(编号:P17001)联合资助。

摘　　要：准噶尔盆地北部乌伦古坳陷历经40余年油气勘探尚未实现工业突破,2016年在石北凹陷准北1井三叠系首次获得天然气发现,因而厘清天然气成因和气源岩对于评价油气勘探潜力和规模意义重大。系统收集了乌伦古坳陷及周缘的天然气地球化学数据,基于天然气碳同位素、轻烃组成认识准北1井天然气特征及类型,基于3个石炭系、1个二叠系烃源岩样品的封闭体系生烃模拟实验结果开展准北1井气源对比分析,并结合地震剖面、区域磁力异常等资料对天然气成因机制作了探讨。结果表明:①准北1井天然气具有甲烷含量低、干燥系数低、氮气含量较高、乙烷碳同位素偏重(δ^(13)C_(2)为-26‰)的特征,轻烃中甲基环己烷含量较高(63.6%),属于腐殖型热解气。②石北凹陷北部发育区域性大断裂,沿断裂发育的闪长岩侵入体造成的岩浆脱气作用是准北1井天然气中氮气含量较高的主要原因。③准北1井天然气与下石炭统滴水泉组烃源岩生烃模拟产物的碳同位素特征相似,表明两者具有一定亲缘性,推断天然气主要来自于滴水泉组海陆过渡相成熟烃源岩。紧邻滴水泉组烃源岩的圈闭是乌伦古坳陷天然气藏勘探的重要方向。After more than 40 years of oil and gas exploration,it has not yet made a industrial breakthrough in Ulungu Depression,northern Junggar Basin.In 2016,the first natural gas reservoir was found in the Triassic system of Shibei Sag.Therefore,it is of great significance to clarify the origin of natural gas and gas source rocks for evaluating the potential and scale of oil and gas exploration.The geochemical data of natural gas in Ulungu Depression and its surrounding areas are systematically collected.The characteristics and types of natural gas in Well Zhunbei-1 are recognized based on the analysis of compositions of natural gas,carbon isotope and light hydrocarbon.Based on the results of closed system hydrocarbon generation simulation experiment of three Carboniferous and one Permian source rock samples,the gas-source rocks correlation in Well Zhunbei-1 is carried out with the carbon isotope compositions of methane,ethane and propane,and the genetic mechanism of natural gas is analyzed in combination with seismic profile,regional magnetic anomaly and other data.The results show that:(1)The natural gas of Well Zhunbei-1 is characterized with low methane content(54.5%-73.9%),low drying coefficient(<0.95),high nitrogen content(11.1%-32.7%),heavy ethane carbon isotope(-26‰),and high content of methyl cyclohexane(MCC6)in light hydrocarbons(63.6%),belonging to humic pyrolysis gas.(2)Several regional large faults are developed in the north of Shibei Sag.Influenced by the diorite intrusions,organic matter was thermally catalyzed,and nitrogen-rich natural gas was formed by magmatic degassing.Combined with regional analysis,it is considered that the magmatic degassing caused by diorite intrusions developed along the faults is the main reason for high nitrogen content in natural gas of Well Zhunbei-1.(3)The carbon isotope characteristics of the natural gas in Well Zhunbei-1 are similar to those of the hydrocarbon generation simulation products of the source rocks of the Lower Carboniferous Dishuiquan Formation(withδ^(13)C_

关 键 词：天然气 氮气 成因 生烃模拟 石炭系 石北凹陷 乌伦古坳陷 准噶尔盆地 

分 类 号：TE122.1[石油与天然气工程—油气勘探]