羌塘盆地羌地18井上二叠统那益雄组烃源岩地球化学特征及意义

Geochemical Characteristics and Significance of Source Rocks of Upper Permian Nayixiong Formation in QD18 Well, Qiangtang Basin

关键词:  羌塘盆地  二叠系  那益雄组  烃源岩  有机质丰度

Key words:  Qiangtang Basin  Permian  Nayixiong Formation  source rocks  abundance of organic matter

摘要:

为进一步厘清羌塘盆地古生界烃源岩条件及油气勘探前景，以羌地18井钻遇的古生界上二叠统那益雄组黑色泥页岩为研究对象，通过岩石热解、元素分析、干酪根镜鉴，结合饱和烃色谱-质谱分析，评价那益雄组烃源品质，研究烃源岩的发育环境和演化过程，探讨羌塘盆地古生界油气勘探前景。结果表明：(1) 羌地18井那益雄组黑色页岩的TOC介于0.58%～6.74%之间，平均值为1.5%；有机质组成以镜质组为主，部分样品以腐泥组为主，H/C原子比介于0.42～0.81之间，O/C原子比介于0.08～0.28之间，干酪根类型指数TI介于－75.25～38.50之间，干酪根类型属于II₂-Ⅲ型，以Ⅲ型为主；R_O介于1.44%～2.01%之间，T_max值介于455～544℃之间，主体进入高成熟演化阶段，部分达到过成熟阶段，以生凝析油、湿气为主；(2) 生物标志物揭示那益雄组沉积时水体为还原环境，具有混合物源特征。(3) 羌塘盆地二叠系发育有效烃源岩，盆地东部的有机质丰度明显高于盆地西部，羌地18井中有效烃源岩厚度最大，达到212 m，以中等烃源岩为主，部分达到优质烃源岩标准，优质烃源岩共发育4段，累计厚度达51.9 m，具有良好的生烃潜力及勘探前景，可以作为后续羌塘油气勘探的目标层系。

Abstract:

To further clarify the conditions of Paleozoic source rocks and the prospect of oil and gas exploration in Qiangtang Basin, the black mud shale of Upper Permian Paleozoic Nayixiong Formation, which was drilled into QD18 Well, was taken as the research object. Through rock pyrolysis, elemental analysis, kerogen identification, combined with saturated hydrocarbon chromatography-mass spectrometry, the source quality of Nayixiong Formation was evaluated, and the development environment and evolution process of source rocks were studied. The exploration prospect of Paleozoic oil and gas in Qiangtang Basin is discussed. The results show that: (1) The TOC of the black shale of Nayixiong Formation in QD18 Well is between 0.58% and 6.74%, with an average value of 1.5%. The organic matter composition is mainly vitrinite, some samples are mainly sapropelic, H/C atomic ratio is between 0.42～0.81, O/C atomic ratio is between 0.08～0.28, kerogen type index TI is between －75.25～38.50, kerogen type belongs to type II₂-Ⅲ, mainly type Ⅲ. The R_o was between 1.44% and 2.01%, and the T_max was between 455 and 544℃. Most of them entered the stage of high maturity evolution, and some reached the stage of over-maturity, mainly condensate and moisture. (2) Biomarkers revealed that the water body of Nayixiong Formation was a reducing environment with the characteristics of mixture source. (3) Effective source rocks are developed in the Permian of Qiangtang Basin, and the abundance of organic matter in the eastern part of the basin is significantly higher than that in the western part of the basin. The thickness of effective source rocks in QD18 Well is the largest, reaching 212 m. There are four high-quality source rocks developed in total, and the accumulated thickness of high-quality source rocks is 51.9 m, which has very good hydrocarbon generation potential and exploration prospect. It can be used as target strata for subsequent Qiangtang oil and gas exploration.