雪峰山西侧地区下寒武统牛蹄塘组烃源岩特征与油气地质意义

    Characteristics and hydrocarbon significance of the source rocks of Lower Cambrian Niutitang Formation on the western side of the Xuefeng Mountain

    • 摘要: 通过对雪峰山西侧地区下寒武统牛蹄塘组烃源岩的系统观测、采样和有机地球化学研究,总结了烃源岩的分布规律、有机质母质类型、烃源岩形成与沉积环境的关系、有机质成熟度等。牛蹄塘组烃源岩具有高有机碳、低氯仿沥青“A”、低生烃潜能的特征,有利烃源岩主要分布在黔北遵义、黔东天柱—城步、渝东南—湘西酉阳—麻阳一带及鄂西咸丰—张家界一带。干酪根镜下鉴定表明,有机质以腐泥组为主(75%~93%),饱和烃/芳烃占0.84%~27%,平均5.77%,牛蹄塘组烃源岩有机质类型为Ⅰ型。干酪根δ13Corg较轻,为-34.99‰~-25.36‰,平均-31.80‰,显示沉积母质以浮游生物及海洋性自养菌为主,部分样品有机质来源以藻类为主,结合Pr/ph分析,烃源岩主要形成于缺氧且通常是超盐度的环境中。沥青反射率为2.23%~4.32%,平均3.45%,等效镜质体反射率为1.84%~3.23%,平均2.43%,表明大部分样品已达到过成熟阶段。

       

      Abstract: Based on systematic observation, sampling and organic geochemical studies of Lower Cambrian Niutitang Formation source rocks on the western side of the Xuefeng Mountain area, this paper summarized such problems as source rocks distribution, organic matter types, the formation of source rocks and sedimentary environment, and the maturity of organic matter. Source rocks of Lower Cambrian Niutitang Formation are characterized by high organic carbon, low chloroform bitumen "A" and low hydrocarbon generation potential. The favorable source rocks are mainly distributed in Zunyi area of northern Guizhou, Tianzhu-Chengbu area of eastern Guizhou, Youyang-Mayang area of southeastern Chongqing-western Hunan and Xianfeng-Zhangjiajie area of western Hubei. Microscopic examination of kerogen reveals that organic matters are mainly sapropelinite(75%~93%) and saturated hydrocarbon/aromatic hydrocarbon(0.84%~27%, 5.77% on average), and the black shale organic matters are of type I. The values of Kerogen δ13Corg is relatively low, varying from -34.99‰ to -25.36‰, -31.80‰ on average, suggesting that the sedimenatry parent materials are mainly marine plankton and maritime bacteria, with marine algae being the source of part of the organic matter. In combination with Pr/ph analysis, the source rocks of Niutitang Formation were mainly formed in an anoxic and hypersaline environment. The bitumen reflectance values vary from 2.23% to 4.32%, 3.45% on average, and the vitrinite reflectance equivalent values vary from 1.84% to 3.23%, 2.43% on average, implying that most of the samples reached the overmature stage.

       

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