东濮凹陷文留构造东营组油藏油-源对比及注入史研究

Study on the oil-source correlation and charging history of the Dongying Formation reservoirs in the Wenliu Structure of the Dongpu Sag,the Bohai Bay Basin

渤海湾盆地东濮凹陷文留构造古近系东营组主要由一套河流-冲积扇沉积体系的浅棕色砂泥岩组成。饱和烃气相色谱及甾类和萜类色-质分析显示,东营组含油砂岩具有伽马蜡烷含量高、姥鲛烷/植烷比值较低、甾烷C29aaa20S/(20S+20R)等成熟度指标值相对较低等特点。油-源对比显示,东营组原油与沙河街组三段源岩具有较好的亲缘关系。根据有机包裹体均一温度、埋藏史及古地温恢复结果和含油砂岩地球化学特征综合分析,认为东营组油气充注时期为东营组沉积后期到华北运动Ⅱ幕的构造抬升初期,油气持续充注时间约5.6 M a。在构造抬升中、后期,东营组上部近1000 m地层被剥蚀,使东营组储层孔隙中的烃类受到不同程度的生物降解,但是储层中包裹烃的正构烷烃分布基本完整。新近纪以来,东营组埋藏不断增加,油气藏进入调整与保存阶段。

The Dongying Formation in Wenliu structure of Dongpu sag, Bohai Bay Basin, consists mainly of light brown sand-shale of alluvial fan depositional system. Saturated hydrocarbon chromatograms and Terpanes ＆ Steranes mass chromatagrams reveal that the oil-bearing sandstone in the Dongying formation features in high gammacerane, low pristane/phytane ratio, and relatively low ratio of C29aaa20S/（20S ＋ 20R） steranes and other mature indexes. Oil-source correlation indicates that oil from the Formation has a relatively close parentage relationship with the Es^3 source rock. A comprehensive analysis of the homogenization temperature of organic inclusions, burial history and palaeogeothermal reconstruction,and geochemical characteristics of oil-bearing sands suggests that continuous oil charging lasted about 5.6 Ma. During the middle and late periods of tectonic uplifting, about 1 000 meters of the upper part of the Dongying Formation was denuded, causing the crude in the Formation biodegraded to different degrees, but leaving the normal alkanes distribution of inclusions basically intact. Since the Neogene, the burial depth of Dongying Formation has been increasing continuously, and the reservoirs has stepped into the stage of adjustment and preservation.