基于变分模态分解的米兰科维奇旋回划分厚层砂砾岩地层层序的方法及其应用

Division method and its application for thick glutenite stratigraphic sequence by Milankovitch cycles based on variational mode decomposition

在利用常规测井曲线对厚层砂砾岩储层进行层序细分的过程中,存在界面不清楚、划分标准难以确定的问题,而米兰科维奇旋回作为沉积地层中的一种重要地质事件,在漫长的地质历史时期中具有相对的稳定性,这种特性使得在米氏旋回约束下的层序划分具有更高统一性。利用变分模态分解(VMD)方法对松辽盆地徐家围子断陷营城组四段(营四段)厚层砂砾岩地层中米兰科维奇旋回进行时频分析,提取与米兰科维奇天文周期对应的高频分量,从而实现层序的划分。结果表明:使用变分模态分解(VMD)方法对测井曲线进行处理,对研究区自然伽马曲线进行VMD分解可得到若干个特征分量,通过对比,100 ka周期对应IMF1分量;根据IMF1曲线形态并结合岩性将营四段细分为21个五级层序,并将其组合为6个四级层序,在四级层序界面处,曲线形态发生明显的突变,表现出明显的周期振荡并且有较大的响应幅度。VMD方法在营四段的应用表明,此方法能够对不同尺度的米兰科维奇旋回进行精准识别和划分,并具有较高的精度和可重复性,研究成果可用于砂砾岩地层的高频层序划分。

In the process of sequence subdivision of thick glutenite reservoirs via conventional logging curves,there are problems of unclear boundaries and determination challenge of classification criteria.However,as an important geological event in sedimentary strata,Milankovitch cycle is characterized by relative stability in a long geological history,which makes sequence division constrained by Milankovitch cycles have higher unity.Variational mode decomposition(VMD)method is used for time-frequency analysis of Milankovitch cycles in thick glutenite strata of the fourth member(Ying-4 Member)of Yingcheng Formation in Xujiaweizi Rift of Songliao Basin,and high-frequency components corresponding to Milankovitch astronomical periods are extracted so as to realize sequence division.The results show that,by using VMD method to process logging curves,several characteristics components of GR curve in studied area are obtained by VMD decomposition.The ratios shows 100ka cycle corresponding to IMF1 component.According to IMF1 curve shape and combined with lithology,Ying-4 Member is subdivided into 21 fifth-order sequences,and they are combined into 6 fourth-order sequences.At the boundaries of fourth-order sequences,curve shape has abrupt changes,showing obvious periodic oscillation with large response amplitude.Application of VMD method in Ying-4 Member shows that this method identifies and divides Milankovich cycles with different scales,with high accuracy and repeatability.The research results can be used in high-frequency sequence division of glutenite strata.