早古生代烃源形成的生物组合及其意义

doi:10.11743/ogg20160501

摘要/Abstract

摘要： 早古生代生物的富集和埋藏为油气资源提供了雄厚的物质基础。不同生物对烃类贡献的差异使成烃生物组合成为烃源岩研究的重要内容，也是高演化烃源岩评价的一个新手段。从地质历史生物演化来看，藻类是早古生代最主要的成烃生物先质，按照生活习性，它们可以分为底栖藻类和浮游藻类。底栖藻类主要生活在海岸带，成带状分布，主要受光的强度、基底情况等因素控制；浮游藻类主要生活在表层水体，它们在不同海域的分布主要受藻体大小和风浪强度控制。依据对塔里木盆地北缘4条下古生界露头剖面的7个地层组中成烃生物的辨识及有机质地球化学特征的研究，总体显示以底栖藻类为主的烃源岩的有机碳含量高于以浮游藻类为主的烃源岩，除形成环境的因素外，成源和生烃过程均有影响，但后者对有机质的碳同位素值影响较小。烃源岩干酪根碳同位素值（δ¹³C_干酪根）与成烃生物组合面貌对比研究发现，以底栖藻类为主的烃源岩的δ¹³C_干酪根小于-34‰；以浮游藻类为主的烃源岩的δ¹³C_干酪根大于-30‰。对比塔里木盆地已发现原油的碳同位素值（均重于-30‰），推断其原油主要来源与浮游藻类密切相关，揭示了下古生界具有较低有机碳含量但以浮游藻类为主的源岩具有很大的生烃能力。

关键词: 成烃生物, 有机碳含量, 干酪根碳同位素值, 油-源对比, 早古生代, 塔里木盆地

Abstract: The accumulation and preservation of the Paleozoic organisms provided a solid organic matter foundation for hydrocarbon generation during the Paleozoic.As different types of organisms were considered to contribute differently to hydrocarbon-generation,a study on organism assemblages (HGOs) started to prevail in source rock researches and has been used a new means of assessing the quality of matured source rocks.From geological,historical,and organic evolution perspectives,algae are the most important material providers for hydrocarbon generation during the early Paleozoic.They can be classified into two types according to their living habit:the benthic and the planktonic algae.The former lived near coast in a zonal distribution in accordance with light intensity and nutrient conditions.The latter lived in a photic zone and their distribution was controlled by their sizes and wind wave strength.Study on the HGOs and the organic geochemical characteristics of the source rock samples from seven formations of four Paleozoic outcrop sections shows that the TOCs in the source rocks dominated by benthic algae are higher than those controlled by planktonic algae.Together with depositional settings,the digenesis and hydrocarbon generation processes were all thought to have played some parts in shaping the organic carbon isotopic compositions of the samples.However,the processes seemed to have exerted lesser effect.Comparison of the kerogen carbon isotopic composition and the HGOs assemblages of the samples indicates that the δ¹³C_kerogen values of samples dominated with benthic algae are less than -34‰,whereas the δ¹³C_kerogen values of source rocks dominated with planktonic algae are more than -30‰.Taking the fact that the δ¹³C values (all more than -30‰) of known oil samples in the Tarim Basin into consideration,this article concludes that the crude in the basin is mostly sourced from rocks with planktonic algae and the source rocks with lower TOCs and planktonic algae from the Paleozoic may have greater exploration potential.

Key words: hydrocarbon generating organism, TOC, kerogen carbon isotope, oil-source correlation, Early Paleozoic, Tarim Basin

中图分类号:

TE122.1

刘文汇,胡广,腾格尔,等. 早古生代烃源形成的生物组合及其意义[J]. 石油与天然气地质, 2016, 37(5): 617-626. doi: 10.11743/ogg20160501 Liu Wenhui,Hu Guang,Tenger,et al. Organism assemblages in the Paleozoic source rocks and their implications[J]. Oil & Gas Geology, 2016, 37(5): 617-626. doi: 10.11743/ogg20160501

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