东营凹陷王家岗孔店组油气成因解析

Origin of the Deep Oils from Kongdian Formation, Dongying Depression, Bohai Bay Basin

东营凹陷南斜坡东段王家岗地区孔店组原油特征明显不同于沙河街组为主的上部层系。孔店组原油具有高含蜡量、低含硫特征;多项生物标志物成熟度指标一致显示其成熟度高于上部层系,反映母源岩相对较高的成熟度。同区沙河街组原油具有相对低蜡、高硫、低熟—中等成熟等相反的特征,表明研究区内孔店组、沙河街组原油为不同成因原油。油—油、油源对比显示孔店组原油既有沙四段烃源岩的典型特征(如高含量伽玛蜡烷),也有沙四段烃源岩不具备而孔店组烃源岩具备的特征(如C29-规则甾烷优势)。正构烷烃单体烃同位素δ13C值揭示孔店组原油与沙河街组原油有别,与深层孔店组烃源岩接近。综合研究认为,王家岗地区孔店组原油具有混源性,油气主要来自深层沙四段、孔二段烃源岩。研究区孔店组油气的发现及其与以往发现油气的不同表明深层另一套烃源岩的存在及广阔的深层油气勘探前景。

The oils from Kongdian Formation of Paleogene in the Eastern Dongying South Slope are quite different from the overlapped Shehejie and Guantao Formation. The oils of Kongdian Formation are characterized by high concentration of wax （28.85 - 31.70% ） ,low content of sulphur （0.04 -0.44% ） with the ratios of C29ααα20S/（20S ± 20R） and C31 hopane 22S/（22S ＋22R） of 0.46 -0.52 and 0.6 -0.65 ,respectively, suggesting relative high maturity. On the contrary, the overlapped Shahejie and Guantao Formations have features of relative low content of wax while high sulphur content with marginal to middle mature maturity. The differences between Kongdian and Shahejie Formations suggest different source rocks of the oils. Results of oil-source rock correlation show that the oils of Kongdian bear typical features of both Es4 and Ek2 source rock, i.e. high Gammacerane concentration of Es4 and predominant C29-steranes of possible Ek2. We suggest that the oils of Kongdian are mixed oils sourced from deep Es4 and Ek2. The oils discovered from Kongdian Formation show the existence of another one set of deep source rock at least and good prospect of deep oils in the study area and the Dongying Depression.