断陷盆地斜坡带三角洲前积型层序精细对比方法——以渤海SZ油田东营组二段下亚段为例

Delta progradational fine sequence correlation method for the slope belts of fault basin:A case study of the lower second Member of the Palaeogene Dongying Formation in Bohai SZ oilfield

断陷盆地斜坡区地形坡度变化较大,地层厚度有一定差异,实现层序等时对比有一定困难。以渤海SZ油田东营组二段下部I、Ⅱ油层组为例,基于高分辨率层序地层学、沉积学、地震沉积学等,利用测井、地震、岩心等资料,识别出研究区目的层为三角洲前缘前积型层序;通过分频解释与地震正演模拟等,确定了前积层类型为无顶积层型。在标志层的控制下,通过地震反射轴形态将SSC1、SSC4短期旋回平面上划分为单相位轴、复相位轴、分叉单相位轴与分叉复相位轴等4个区域,提出了分区域前积角度计算方法,即在目的层顶部标志层拉齐的情况下,通过地震剖面与井间剖面相结合,依据前积层井间厚度变化确定各区域前积角度;由于单相位轴区域近似等厚,采用了近水平模式对比。按照不同级次基准面旋回的变化,将研究区目的层划分为2个中期(MSC)、14个短期(SSC)和26个超短期(SSSC)基准面旋回,建立了中期、短期基准面旋回高分辨率等时地层格架,并完成了超短期旋回的等时对比。

The topographic slope changes greatly and the stratigraphic thickness varies to certain extent in the slope belts of fault basin,which brings difficulty in the sequence isochronous contrast analysis.In the case of the I and II reservoirs of the lower part of the second Member of the Palaeogene Dongying Formation of Bohai SZ oilfield,the target layer of the study area is identified as delta front progradational sequence by using data of logging,seismic and core,and based on high resolution sequence stratigraphy,sedimentology,and seismic sedimentology.The type of foreset bed is determined to be free of topset bed through seismic forward modeling and frequency division interpretation.Under the control of marker layers,SSC1 and SSC4 short-term cycle planes are divided into single-phase axis region,complex-phase axis region,bifurcate single-phase axis region and bifurcate complex-phase axis region according to the shape of seismic reflection axis.The region-based progradation angle calculation method is proposed.In other words,under the condition that the marker layer at the top of the target layer is flush,the progradation angle in each region can be determined by combining the seismic profile with the cross-well section according to the variation of interwell thickness in foreset bed.Because the single-phase axis region is of approximately equal thickness,the near-horizontal mode comparison is adopted.The target layer of the study area can be divided into 2 medium-term base level cycles(MSC),14 short-term base level cycles(SSC)and 26 super-short term base level cycles(SSSC)according to the changes in base level cycles of different grades.The high resolution isochronal stratigraphic framework of medium-term and short-term base level cycles is established,and the isochronous correlation of super-short term base level cycles is fulfilled.