渤海始新统沙四段层序地层特征及与周边油区的对比

渤海湾盆地始新统沙四段(沙河街组四段)形成时的构造背景特点决定了它的复杂性、多变性和多样性。沙四段在其建组剖面分为沙四上、中和下三个亚段。随着新钻井的增多和研究的不断深入,渤海沙四段层序地层的认识也在不断加深。渤海以前的沙四段基本没有分出亚段,只是分出了南北两种类型。现在认为渤海发育完整的沙四段,分为上下两个亚段,下部为蒸发盐湖相沉积,上部为正常的砂泥岩沉积。南部发育完整的沙四段,北部只钻遇了沙四上亚段,可能缺失沙四下亚段;上下亚段以假整合接触,南北地层是统一的,而不是两种类型。沙四下亚段相当于济阳坳陷典型沙四段中、下两个亚段。沙四段分为继承和残留两种类型,二者有很大的差别。沙四段下亚段不具备生油能力,上亚段发育完整的生储盖组合,可以形成自生自储的油气田,是深层勘探的重要方向之一。

THE CHARACTERISTICS OF THE MEMEBER 4 OF SHAHEJIE FORMATION IN BOHAI BASIN AND ITS CORRELATION WITH NEIGHBOURING OILFIELDS

The complex tectonic background of the Bohai Basin during the deposition of the member 4 of the Shahejie Formation(Sha-4 Member)means that this stratigraphic unit is spatially complex and variable.At its type section in the Jiyang Depression,the member 4 can be divided into the upper,middle and lower sub-members.With increasing borehole data and further investigation,our understanding of the member 4 of the Shahejie Formation has been improved.In the past,the member 4 was not subdivided into submembers and it was recognized as two types in the southern and northern Bohai Basin.With new data and complete successions,the member 4 in the Bohai Basin can be divided into,we can now divide this member into the upper and lower sub-members,which were deposited in very different conditions.The lower sub-member is characterized by evaporitic lacustrine deposits,whereas the upper sub-member is characterized by sandy mudstones.Drill holes in the southern Bohai Basin have penetrated the entire Member 4,whereas drill holes in the northern Bohai Basin only penetrated the upper sub-member and the lower sub-member is probably missing.Regardless,the lithostratigraphy of the Member 4 is comparable in the southern and northern Bohai Basin.The lower sub-member 4 in the Bohai Basin can be correlated with the upper and lower sub-members in the Jiyang Depression.The lower sub-member in the Bohai Basin is not an ideal target for petroleum exploration,whereas the upper sub-member has a suite of cource-reservoir-cap rocks and should be a exploration target.