渤海湾盆地沧东凹陷孔二段细粒相区有机地球化学特征

Organic geochemistry characteristics of the fine grained sedimentary rock of the second member of Kongdian Formation(Ek_2)in Cangdong Sag,Huanghua Depression,Bohai Bay Basin

渤海湾盆地沧东凹陷孔二段(Ek_2)页岩油勘探取得重要进展,多口井在页岩段获得工业油流,孔二段整体被视为常规烃源岩段,其内部岩性及有机地球化学特征尚未开展过深入研究。为此,从沧东凹陷G108-8井、普通薄片、全岩X-射线衍射、有机碳、镜质体反射率、岩石可溶有机物族组分、饱和烃色谱及饱和烃质谱等多种化验资料出发,对孔二段细粒相区泥页岩岩性及其有机质地球化学特征进行系统评价。研究结果表明:孔二段常规泥页岩段岩石矿物成分复杂,无明显优势矿物存在;孔二段有机质丰度高,干酪根类型以Ⅱ_1—Ⅱ_2型为主,有机质成熟度处于低成熟至中等成熟阶段;烃源岩具有明显的植烷优势,除部分样品伽马蜡烷含量较低外,总体指示强还原沉积环境,C_(29)甾烷含量明显高于C_(27)甾烷和C_(28)甾烷,同时C_(27)甾烷也有相对较强的波峰,孔二段烃源岩高等植物有机质输入占优势,同时也有低等水生生物和藻类的贡献。

Shale oil exploration made great progress in the second member of Kongdian Formation in Cang- dong Sag and several wells got industrial oil flow in the shale segment which was considered as hydrocar- bon source rocks.However, the internal lithologic and organic geochemical features have not been studied in-depth.Based on the analysis of conventional thin secti0n,whole rock X-ray diffraction, organic carbon, vitrinite reflectance, soluble organic components of rocks, saturated hydrocarbon chromatography and satu rated hydrocarbon mass spectrometry, the lithology and organic geochemistry characteristics of the fine grained lithologic of the second member of Kongdian Formation in Cangdong Sag were systematically eval- uated.The evaluation results of the second member of Kongdian Formation shows demonstrate complex rock mineral composition,high abundance of organic matter with Type Ⅱ1 and Type Ⅱ2 kerogen,and lowmedium thermal maturity. Normal alkane extract from source rock contains single peak type and double peak type;source rock has phytane advantage and only few samples have low content of gammacerane,indicating strong reducing environments; C29 sterane content is obviously higher than C27 or C28 sterane,C27 sterane also has relatively strong peaks.The organic matter of the second member of Kongdian Formation in Cangdong Sag is mainly from the higher plant,and also has lower aquatic organisms and algaes.