最小含氧带和硫化环境控制14亿年前有机质生烃能力  

OMZ and euxinic sulfidic environments dominating hydrocarbon generation poential of organic matter 1.4 billion years ago

作　　者：王晓梅[1] 张水昌[1] 何坤[1] 王华建 米敬奎[1] 苏劲[1] 叶云涛 Xiaomei Wang;Shuichang Zhang;Kun He;Huajian Wang;Jingkui Mi;Jin Su;Yuntao Ye(Key Laboratory of Petroleum Geochemistry,Research Institute of Petroleum Exploration and Development,China National Petroleum Corporation,Beijing 100083,China)

机构地区：[1]中国石油勘探开发研究院,中国石油集团公司油气地球化学重点实验室,北京100083

出　　处：《科学通报》2021年第23期3005-3017,共13页Chinese Science Bulletin

基　　金：国家重点研发计划(2017YFC0603101);国家重大科技专项(2016ZX05004001);中国科学院A类战略性先导科技专项(XDA14010101);国家自然科学基金(41530317)资助。

摘　　要：显生宙沉积有机质富集和生烃潜力受控于初级生产力和保存环境,但元古宙以原核生物为主的广泛厌氧环境对烃源岩发育的控制作用并不清楚.中国华北燕辽盆地中元古界下马岭组发育一套厚达250 m的富有机质烃源岩,主要形成于硫化厌氧和最小含氧带(oxygen minimum zone,OMZ)水体环境,沉积时限约为1400~1360 Ma.选择有代表性的两类黑色页岩样品开展了黄金管热模拟实验,结果表明,14亿年前富有机质页岩的生油气潜力与显生宙优质烃源岩相当,且明显受控于沉积时的海洋水体环境;硫化厌氧环境的沉积有机质,虽丰度略低(TOC 5%),但生油能力明显高于OMZ环境下的沉积有机质(TOC达12%);两类沉积环境有机质的生烷烃气能力却相反.这说明,厌氧环境不但有利于有机质富集,同时保存了对生油更加有效的富氢脂肪结构;尽管OMZ海洋初级生产力很高,在底层水有氧环境下也能够沉积高丰度的有机碳,但氧化作用使其生油潜力明显降低.研究证实,中元古代海洋环境的动态演化对沉积有机质的母源构成、生烃潜力和产物组成具有重要影响,为深入了解并探索中新元古界的烃源岩发育机制和油气资源潜力提供了一个重要窗口.The enrichment and hydrocarbon potential of Phanerozoic source rocks are mainly governed by primary productivity and sedimentary environment.However,the control of extensive anoxic environment on the development of Proterozoic source rocks induced from prokaryotes origin remains unclear.The Mesoproterozoic Xiamaling Formation(1400-1360 Ma)in the Yanliao Basin,North China has a set of organic-rich source rocks or shales with a depth of~250 m.Their chemical environments of water body include oxygen minimum zone(OMZ),anoxic ferruginous(Fe2+-rich)and euxinic sulfidic(H2 S-rich)depositional conditions.They cover almost all the characteristics of marine water environment so far recorded in Mesoproterozoic.The source rocks are enriched in organic matter.Under its low thermal mature,these rocks preserve abundant original biogenic or organic information,which eliminate the influence of loss or insufficiency of original biogenic information caused by thermal alteration in many Archean and Proterozoic basins.In this study,kerogens from two representative black shale samples developed in euxinic and OMZ environments were separated and applied in gold-tube pyrolysis.To obtain the oil and gas potential from primary decomposition or cracking of kerogens,a step-by-step non-isothermal pyrolysis method was conducted.It showed that the deposition and hydrocarbon potential of organic-rich shale at 1.4 billion years ago were evidently dominated by marine environments.Despite the relatively low TOC content(5%)for original shale,the organic matter(kerogen A)preserved in euxinic environment has higher oil potential compared with that deposited in OMZ(kerogen B)(12%TOC for shale sample).The maximum cumulative yield of oil from kerogen A is 499.2 mg/g TOC,which is about 2.5 times of that from kerogen B(201.6 mg/g TOC).In contrast,the OMZ sample has higher potential for hydrocarbon gas generation.The maximum cumulative yields of hydrocarbon gases from primary cracking of kerogen A and kerogen B are 103.8 and 139.6 m L/g TOC,respectively.As

关 键 词：烃源岩 原核生物 厌氧环境 有氧环境 生油气潜力 降解作用 

分 类 号：P618.13[天文地球—矿床学]