奈曼凹陷九上段米氏旋回识别与地质响应

Identification and geological response of Miki cycle in the ninth uppersection of Naiman Depression

奈曼凹陷九佛堂组上段有着巨大的油气资源前景,由于其沉积岩粒度小、层序界面识别不清等难点,制约了油气勘探推进和烃源岩预测。以奈曼凹陷奈17井为例,对九佛堂组上段自然伽马测井数据进行频谱分析和滤波处理来开展旋回地层学分析。结果显示,该套地层保存完好的米兰科维奇旋回,将长偏心率、短偏心率、斜率的滤波曲线分别作为四、五、六级层序划分的参考曲线,划分出17个四级层序、55个五级层序和138个六级层序,地层沉积主要受控于405 ka长偏心率旋回。结合405 ka滤波曲线和对应深度,对九上段顶部和底部的沉积速率进行计算,沉积速率符合地层属性切片的沉积响应,验证了研究区层序划分的科学性,也为该区细粒层序地层学研究和高频层序划分提供参考。

The upper section of the Jiufotang Formation in the Naiman Depression has great prospects for oil and gas resources,but the small grain size of the sedimentary rocks and the lack of identification of the interfaces of the stratigraphic sequences have constrained the advancement of oil and gas exploration and the prediction of the hydrocarbon source rocks.Taking the Nai No.17 Well in Naiman Depression as an example,the natural gamma logging data of the upper section of Jiufotang Formation were analyzed by spectrum analysis and filtering to carry out cyclic stratigraphy analysis.The results showed that the well-preserved Milankovitch cycle of the strata was divided into 17 fourth-order sequences,55 fifth-order sequences,and 138 sixth-order sequences by using the filtering curves of long eccentricity,short eccentricity,and slope as reference curves for the division of fourth-order,fifth-order,and sixth-order sequences,respectively.The geological sedimentation was mainly controlled by the 405 ka long eccentricity cycle.Combined with the 405 ka filter curves and corresponding depths,the sedimentation rates at the top and bottom of the ninth upper section were calculated,and the sedimentation rates were consistent with the sedimentary response of the stratigraphic attribute slices,verifying the scientificity of the stratigraphic sequence delineation in the study area,and also providing a reference for the study of fine-grained sequence stratigraphy and the delineation of high-frequency stratigraphic sequences in the area.