奈曼北部义县组烃源岩地球化学特征及研究意义

奈曼凹陷北部发育有一套膏盐岩和厚层泥岩,针对该套层位归属不明确、泥岩地球化学特征认识不清等问题,应用古生物孢粉化石鉴定、地层测井与地震特征对比、饱和烃色谱-质谱分析等方法对膏盐岩和厚层泥岩的地层特征、泥岩的烃源岩特征进行研究。研究结果表明:膏盐岩和泥岩属于义县组火山喷发间歇期的沉积产物,泥岩厚度为50～400 m,分布面积约为130 km²,有机碳含量平均为3.40%,有机质类型为Ⅰ、Ⅱ₁型,深度为1 880.00 m处实测R_o平均值为0.5%,处于低成熟—成熟的演化阶段;义县组烃源岩生排烃期早于九佛堂组烃源岩,更有利于油气运移聚集。该研究证实了义县组具备良好的生烃条件,对奈曼凹陷北部深层油气勘探具有重要意义。

Geochemical Characteristics and Research Significance of Source Rocks of Yixian Formation,Northern Naiman

In view of the problems of unclear stratigraphic attribution and unclear geochemical characteristics of the set of gypsum salt rocks and thick mudstones in northern Naiman Sag,the stratigraphic characteristics of gypsum salt rock and thick mudstone and the characteristics of mudstone source rock were studied by means of paleontological sporopollen fossil identification,stratigraphic logging and seismic characteristics comparison,saturated hydrocarbon chromatography-mass spectrometry and so on.The research results show that the gypsum salt rock and mudstone were the sedimentary products of Yixian Formation in volcanic eruption period,with mudstone thickness of 50 to 400 m,distribution area of about 130 km²,3.40%average organic carbon content,Type I andⅡ1 organic matters,and the average measured Ro value of 0.5%at about 1880 m,indicating that they were in low-mature to mature evolution stage.The hydrocarbon generation and expulsion period of the source rocks in Yixian Formation was earlier than that of the source rocks in Jiufotang Formation,which is more conducive to hydrocarbon migration and accumulation.This study proves that Yixian Formation has well developed for hydrocarbon generation,which is of great significance for deep oil and gas exploration in the northern Naiman Sag.