四川盆地灯影组藻云岩无机微量元素特征及生烃潜力预测
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摘要
由于我国古老海相碳酸盐岩烃源岩演化程度高,剩余有机碳含量低,因此在应用常规有机地化指标进行评价时存在较大争议。四川盆地广泛分布的震旦系碳酸盐岩的有机碳含量多处于0.1%—0.5%之间,应用不同的评价标准则结果相差很大。应用一些无机地球化学指标如微量元素、碳氧同位素对四川盆地震旦系碳酸盐岩进行了分析。首先进行各元素含量相关性分析,继而挑选与TOC相关性较好的元素进行了古环境和古生产力的恢复,最后将无机与有机地化指标的结合,划分判识有效烃源岩的TOC下限。结果表明,一些无机地化指标在高演化地层,尤其是碳酸盐岩中仍具备较好的判识能力。Ba含量、δ13Ccarb对古生产力,Th/U、Ce/La值对古氧化还原条件的反映效果均较好。综合有机与无机地化指标;将TOC=0.2%作为四川盆地震旦系灯二段碳酸盐岩烃源岩有机质丰度下限,并认为在以后的高演化碳酸盐岩地层中可应用该类无机地化指标。
There are many disputes on applying organic geochemical indicators to assess,as the evolution degrees of ancient marine carbonate source rocks are high and the residual organic carbonates in these rocks are very low.The contents of organic carbonates in Sinian system of Sichuan Basin mostly range from 0.1% to 0.5% and different evaluation criteria result in different conclusion.Some inorganic geochemistry indicators as rare element,carbon and oxygen isotopes are used to analyze the carbonate in Sinan system of Sichuan basin.Firstly the correlation analysis of the content of individual elements were done,and then some were picked out which has good correlation with TOC to recovery the paleoenviroment and paleoproductivity,Lastly inorganic and organic geochemistry index were integrated to classify and identify the threshold value of TOC of effective hydrocarbon source rocks.The results show that some indicators still have good ability of identification in high evolution strata especially carbonate rocks,such as the content of Ba,δ13Ccarb correspond to paleoproductivity,the value of Th/U and Ce/La indicate the ancient redox conditions,which all manifest good result.Therefore,TOC equals 0.2% can be used as the threshold value of organic enrichment of carbonate source rocks in Second Dengying formation of Sinian system of Sichuan basin,beyond that,such inorganic geochemistry indicator could be applied into the carbonate formation which have high evolution degrees later.
There are many disputes on applying organic geochemical indicators to assess,as the evolution degrees of ancient marine carbonate source rocks are high and the residual organic carbonates in these rocks are very low.The contents of organic carbonates in Sinian system of Sichuan Basin mostly range from 0.1% to 0.5% and different evaluation criteria result in different conclusion.Some inorganic geochemistry indicators as rare element,carbon and oxygen isotopes are used to analyze the carbonate in Sinan system of Sichuan basin.Firstly the correlation analysis of the content of individual elements were done,and then some were picked out which has good correlation with TOC to recovery the paleoenviroment and paleoproductivity,Lastly inorganic and organic geochemistry index were integrated to classify and identify the threshold value of TOC of effective hydrocarbon source rocks.The results show that some indicators still have good ability of identification in high evolution strata especially carbonate rocks,such as the content of Ba,δ13Ccarb correspond to paleoproductivity,the value of Th/U and Ce/La indicate the ancient redox conditions,which all manifest good result.Therefore,TOC equals 0.2% can be used as the threshold value of organic enrichment of carbonate source rocks in Second Dengying formation of Sinian system of Sichuan basin,beyond that,such inorganic geochemistry indicator could be applied into the carbonate formation which have high evolution degrees later.
引文
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12 Elderfield H and Greaves M J.The rare earth elements in seawater.Nature,1982;296:214—219
2姚建军,陈孟晋,华爱刚,等.川中乐山-龙女寺古隆起震旦系天然气成藏条件分析.石油勘探与开发,2003;30(4):7—9
3 Hunt J M.Petroleum Geochemistry and Geology.New York:W HFreeman,1979;118—160
4程克明,王兆云.高成熟和过成熟海相碳酸盐岩生烃条件评价方法研究.中国科学,D辑,1996;26(6):537—543
5张水昌,梁狄刚,张大江.关于古生界烃源岩有机质丰度的评价标准.石油勘探与开发,2002;29(2):8—12
6叶连俊.生物有机质成矿作用和成矿背景.北京:海洋出版社.1998:335—352
7腾格尔,刘文汇,徐永昌,等.高演化海相碳酸盐岩烃源岩地球化学综合判识—以鄂尔多斯盆地为例.中国科学,D辑,2006;36(2):167—172
8颜佳新,徐四平,李方林.湖北巴东栖霞组缺氧沉积环境的地球化学特征.岩相古地理,1998;18(6):27—32
9赵振华.微量元素地球化学原理.北京:科学出版社,1997:61—80
10 McLennan S M.Rare earth elements in sedimentary rocks:Influ-ence of provenance and sedimentary processes.In:Lipin B R,McKay G A,eds.Geochemistry and Mineralogy of Rare Earth Ele-ments.Rev Min Geochem,1989;21:169—200
11 Wright J,Holser W T.Paleoredox variations in ancient oceans recor-ded by rare earth elements in fossil apatite.Geochim.et Cosmo-chim.Acta.,1987;51:631—644
12 Elderfield H and Greaves M J.The rare earth elements in seawater.Nature,1982;296:214—219
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