涠西南凹陷西部古近系流一段三角洲前缘滑塌浊积岩分布规律

Fluxoturbidite distribution for Paleogene Liu-1 Interval West delta front,Wei South-west Depression

涠西南凹陷古近系流一段沉积时期在盆地西部发育了规模巨大的三角洲沉积。根据地震反射特征,结合测井曲线小波变换分析、地震资料时频分析以及测井约束波阻抗反演资料的时间切片和沿层切片分析,建立了西部流一段三角洲高精度层序地层格架,共划分出10个五级层序。根据平均波峰振幅、能量半衰时和瞬时频率等地震属性以及平均波阻抗特征,结合测井约束波阻抗反演剖面,在测井和录井资料的标定下,对10期三角洲—滑塌浊积岩沉积体系进行了识别,发现西部流一段三角洲在发育过程中具有整体持续推进、主体左右摆动、前缘浊积岩发育的特征。由于受三角洲发育过程中前缘斜坡的坡度角变化的影响,滑塌浊积岩主要形成于三角洲发育的中期。西部流一段三角洲斜坡带存在两个明显的地形坡度突然变缓的转折点,是滑塌浊积岩的两个主要集中带。第一集中带滑塌浊积岩邻近三角洲沉积体分布;第二集中带滑塌浊积岩主要分布在流一段三角洲前缘前方2000～4000m范围内,该距离与前缘坡度角存在定量关系。

A very large scale of delta sediment was developed in the west of the basin at the deposition period of Paleogene Liu-1 Interval in Wei South-west Depression.According to seismic reflection characteristics and by joint application of the well logging wavelet transform analysis,the seismic time-frequency analysis,and the analysis of slices and stratigrafic slices of well logging constraint impedance inversion,the high precision sequence stratigraphic framework was established in Liu-1 Interval west delta,10 5th class sequences were classified.According to the characteristics of average peak amplitude,energy half time,instantaneous frequency and other seismic attributes,and the average wave impedance characteristics,and by combining with log-constrained inversion profiles,the 10 stages of the delta-fluxotubidite sedimentary systems were recognized under the calibration of logging data.It was found out that during the delta development process it showed the such characteristics as whole body continuously moving forward,main body wagging and front edge turbidity developing.Due to the influence of the slope angle variation of the foreslope during the delta' development process,the main development stage of the fluxotubidite was in the middle stage of the delta development.In the Liu-1 Interval West delta zone there are two obvious turning points at which the terrain slope suddenly slows,Around the two points are the two major concentration zones for the fluxotubidite.The first fluxotubidite concentration zone neighbors delta sediment distribution,while the second one mainly distributes in the area which is around 2000～4000m from the front of the Liu-1 Interval delta.There is a quantitative relationship between the distance and the front edge slope angle.