非洲Melut盆地北部不同地区原油有机地球化学特征及意义  

Organic geochemical characteristics and significance of crude oils in different areas in the northern Melut basin,Africa

作　　者：史忠生[1] 程顶胜[2] 白洁[1] 庞文珠 陈彬滔[1] 薛罗[1] 马轮[1] Shi Zhongsheng;Cheng Dingsheng;Bai Jie;Pang Wenzhu;Chen Bintao;Xue Luo;Ma Lun(PetroChina Research Institute of Petroleum Exploration and Development-Northwest,Lanzhou,Gansu 730020,China;PetroChina Research Institute of Petroleum Exploration and Development,Beijing 100083,China;China national oil and gas exploration and development corporation,Beijing 100034,China)

机构地区：[1]中国石油勘探开发研究院西北分院,甘肃兰州730020 [2]中国石油勘探开发研究院,北京100083 [3]中国石油国际勘探开发有限公司,北京100034

出　　处：《地质学报》2023年第5期1598-1609,共12页Acta Geologica Sinica

基　　金：国家科技重大专项“海外重点探区目标评价与未来领域选区选带研究”(编号2016ZX05029005);中国石油天然气集团有限公司“南苏丹-苏丹重点盆地勘探领域评价与目标优选”项目(编号2019D-4306)联合资助的成果。

摘　　要：为了明确Melut盆地北部不同地区原油母质来源、沉积环境及亲缘关系,采用饱和烃色谱及色谱-质谱方法,开展了盆地北部不同地区原油地球化学特征分析及对比。研究表明,盆地北部各地区原油正构烷烃无明显奇偶优势,Ts/Tm值1.36~3.47、C_(31)升藿烷22S/(22S+22R)比值0.54~0.60、αααC_(29)20S/(20S+20R)与C_(29)αββ/(ααα+αββ)比值大于0.4,总体表现为成熟原油;伽马蜡烷指数普遍小于0.1,C_(21)三环萜烷具有明显优势,Pr/Ph值0.97~2.31,均值1.61,指示其烃源岩形成于弱还原-弱氧化的淡水湖相环境;生油母质为Ⅱ~Ⅲ型混合型。不同地区原油母质来源及成熟度有差异:Moleeta次凹东坡原油为单峰后峰态分布,高碳数正构烷烃含量占优势,C_(24)TeT/C_(23)TT平均值大于1,具有明显的陆源高等植物贡献,原油成熟度较低,发育重质—中质油;Jamous次凹深洼区原油为前峰优势的双峰态分布,C_(24)TeT/C_(23)TT值小于1,生烃母质除有陆源高等植物贡献外,水生生物也有重要贡献,原油成熟度较高,发育中质—轻质油;Palogue油田位于两个生烃次凹之间,具有混源特征;AYT(Abyat)油田原油主要来自Jamous次凹深洼区,同时有原地烃源岩的生烃贡献。Jamous次凹斜坡中部翘倾断裂带的发育,将次凹分割成两个次级断陷,为斜坡东部AYT地区烃源岩的发育提供了构造条件。翘倾断裂带使Jamous次凹斜坡中部抬升变浅,局部发育弱氧化环境下的浅水砂泥互层沉积。In order to clarify the source,depositional environment and genetic relationship of crude oils in different areas in the northern Melut basin,the geochemical characteristics of crude oils in different areas were analyzed and correlated by means of saturated hydrocarbon chromatography and chromatography-mass spectrometry.The results showed that then-alkanes of crude oils in the northern Melut basin have no obvious odd-even predominance,the Ts/Tm values range from 1.36 to 3.47,the C31hopane 22S/(22S+22R)ratios are from 0.54 to 0.60,and the ratios ofαααC_(29)20S/(20S+20R)and C_(29)αββ/(ααα+αββ)are more than 0.4,all of which indicated that the crude oils in the northern Melut basin are mature oils.The gammacerane index is generally less than 0.1,the C_(21)tricyclic terpanes have obvious predominance,and the values of Pr/Ph range from 0.97 to 2.31,with an average value of 1.61,all of which indicated that the source rocks of these crude oils were formed in the environment of weak reduction-oxidization freshwater lacustrine and developed typeⅡ-Ⅲorganic matter.The source and maturity of crude oils in different areas in the northern Melut basin are different.The crude oils in the eastern slope of the Moleeta sub-sag have a unimodal and post-peak distribution of n-alkane,with a predominance of high carbon number n-alkane and an average value of C_(24)TeT/C_(23)TT being more than 1,which showed that the source rocks of these oils are dominated by terrestrial higher plants.The maturity of crude oil is low,and the heavy-medium oils are generally developed in the eastern slope of the Moleeta sub-sag.The crude oils in the deep area of the Jamous sub-sag have a bimodal distribution ofn-alkane,with a pre-peak predominance,and the value of C_(24)TeT/C_(23)TT is less than 1.In addition to the contribution of terrestrial higher plants,the aquatic organisms also have an important contribution to the source rocks.The maturity of crude oil is relatively high,and the medium-light oils are generally developed in the deep

关 键 词：地球化学特征 生物标志物 原油对比 Melut盆地 

分 类 号：P618.13[天文地球—矿床学]