复合点坝演化模式及成因分析

Evolution Mode and Genesis Analysis of Composite Point Bars

复合点坝是由多期残缺点坝组合在一起形成的复合体,储层内部结构复杂、非均质性强。以往关于点坝的研究,多是从点坝的形态、粒度、规模和水动力成因去分析,极少从点坝形成的“残缺性”做定量研究和成因分析。选取阿尔伯塔盆地下白垩统McMurray组的地震切片、密西西比河New Madrid曲流河段卫星照片、曲流河数值模拟和物理模拟等资料,统计拟合复合点坝演化阶段和复合度的关系,在二维坐标轴投点后,都可以拟合得到一条相似的对数曲线y=−aln x+1。得出复合点坝演化符合以下规律:某一期点坝从形成至被破坏成残缺状态,其残缺程度(复合度)与演化阶段呈对数递减关系。该结论对曲流河理论研究和砂体表征都具有一定价值。

The composite point bar is composed of multi-stage residual bars to form a composite body.The internal structure of the reservoir is complex and highly heterogeneous.In the past,researches on point bars were mostly focused onthe shape,granularity,scale and hydrodynamic force.Quantitative research on and cause analysis on the“incompleteness”of point bars are rare.In this paper,the seismic section of McMurray Formation of early Cretaceous in Alberta Basin,satellite photos of Mississippi River New Madrid meander section,numerical simulation and physical simulation of meander rivers are selected to statistically fit the relationship between the evolution period of composite point bars and the residual degree.A similar logarithmic curve y=−a ln x+1 can be obtained after two-dimensional coordinate axis projection.It is concluded that the evolution of composite point bars is in accordance with the following law:From the formation to the destruction into a defective state of a certain stage point bars,the degree of its defect(composite degree)is logarithmically decreasing with the evolution stage.The conclusion is valuable for the study of meandering river theory and the characterization of sand body.