济阳坳陷古近系二级层序界面厘定及其石油地质意义

Ascertaining secondary-order sequence of Palaeogene in Jiyang depression and its petroleum geological significance

利用地质、地球物理、地球化学和古生物资料,对比分析了沙四段与孔店组、沙四段上亚段与下亚段、沙三段与沙四段界面特征,以及界面上下构造转化、古环境变化情况。结果发现:沙四段上亚段与下亚段不整合特征较沙四段与孔店组、沙三段与沙四段更为明显且分布广泛;在沙四段下亚段—上亚段沉积时期,构造应力发生了较大的转变,断裂活动与盆地伸展特征明显不同,而孔店组与沙四段下亚段、沙四段上亚段与沙三段沉积时期应力背景、构造活动特征相似;温度比值、湿度比值、特征元素比值及化石分布情况也表明,沙四段下亚段—上亚段沉积时期气候环境变化幅度最大。由此认为,济阳坳陷沙四段下亚段与上亚段较沙四段与孔店组、沙三段与沙四段不整合级别高,为二级层序界面;古近系发育3个二级层序,分别对应孔店组—沙四段下亚段、沙四段上亚段—沙二段下亚段、沙二段上亚段—东营组。该认识不仅能够合理解释沙四段上亚段—沙三段岩性变化,而且在该认识指导下部署的多口探井均取得成功,扩展了油气勘探领域。

In order to ascertain the secondary-order sequence boundary of Palaeogene in Jiyang depression, geophysical, geochemical and paleontological data were used to study and compare the feature of three boundaries of upper/lower Es4(the fourth member of Shahejie formation), Es3(the third member of Shahejie formation)/ Es4 and Es4/Ek(Kongdian formation). Tectonic and paleo-environmental changes happened at the three boundaries have been investigated and the results can be concluded as follows: 1unconformity of upper/lower Es4 is more widespread and easier to identify compared with the unconformities of Es3/Es4 and Es4/Ek; 2tectonic stress characteristics indicated by fault activity modes and basin stretch directs were obviously different in the upper and lower Es4 but similar in the lower Es4 and Ek, the upper Es4 and Es3; 3climatic environment change happened at the upper/lower Es4 period was sharper than those happened at the Ek/lower Es4 and the upper Es4/Es3 period. It is ascertained that the order of upper/lower Es4 boundary is a secondary order, which is higher than those of Es4/Ek and Es3/Es4 boundary. Thus, there are three secondary-order sequences in Palaeogene which correspond to lithological stratum of Ek-lower Es4, upper Es4-lower Es2(the second member of Shahejie formation) and upper Es2-Ed(Dongying formation) respectively. The new classification pattern of secondary-order sequence could not only give rational explanation to the lithological change in Es4 but also provide guidance to oil and gas exploration in Es4.