东营凹陷中始新统上部—上始新统层序地层模式及其石油地质意义

Sequence Stratigraphic Model and Its Petroleum Geological Significance of Upper Part of Middle Eocene Series and Upper Eocene Series in Dongying Depression

通过识别沉积基准面旋回产生的层序界面 ,东营凹陷中始新统上部—上始新统可划分出四个层序。各层序具有相似的成因和体系域构成。其低位域 (LST)发育辫状河、下切水道—浊积扇、扇三角洲、废弃型三角洲和水下扇。湖泊扩张体系域 (EST)发育由深湖泥岩、油页岩、白云岩、滨浅湖组成的湖泊体系、破坏型三角洲及曲流河体系。湖泊萎缩体系域 (RST)发育浅湖、河流三角洲体系及扇三角洲体系。由于同一层序在盆地发育的构造部位不同 ,可以表现出三种层序样式 :A位于构造坡折带之下的深湖—三角洲环境层序样式 ,B、位于构造坡折带之上的下切水道—浅湖环境层序样式和C、位于湖域之外的河流—泛滥平原环境层序样式。并在综合研究的基础上建立了东营凹陷中始新统上部—上始新统层序的成因模式。指出在每个三角洲主朵体的前方同生断裂带及其靠近洼陷一侧是低位砂体的主要发育区 ,也是低位砂体油藏的富集区和寻找隐蔽油藏的主要方向。

By identifying sequence boundary generated by base level cycle, the author have reloghizcd fied four sequences in upper part of middle Eocene series and upper Eocene series of Dongying depression. Every sequence has similar genesis and system tract trait. Lowstand system tract (LST) developed braided fluvial, incised channel -turbidity fans,fan deltas,abandoned deltas and subfan . Lacustrine expanding system tract (EST) developed lacustrine system, consisted of deep mudstone, oil shale, dolomite and shallow lacustrine, destroyed deltas and meandering streams. Lacustrine retreating system tract (RST) developed shallow lacustrine, fluvial- delta system, and fan delta system. Because sequence developed in different sites of the basin, the sequence shows three kinds of sequence style: A, deep lacustrine -delta environment sequence style distributing below structure break. B, incised channel -shallow lacustrine environment sequence style distributing upward structure break. C, fluvial-flooding plain sequence environment style distributing beyond lacustrine. Based on comprehensive research, this paper has built up the genetic model of upper part of middle Eocene series and upper Eocene series in Dongying depression .The model indicates that sequence generation was controlled by third cycle of base level as a function of tectonic movement and climate. Because water volume of lake is finite, tilting and faulting redistributes the lake water toward increased accommodation space area, base level fell to generate lowstand system tract characterized by incised channel and turbidity fan. In the inactive epoch faulting of, base level, affected by climate, rise rapidly to generate lacustrine expanding system tract characterized by lacustrine facies spreading. When the lake level recovering to the situation before faulting, base level arrived at summit and began to fall, because faulting made topography steep, sedimentary supplied enough, lacustrine retreating system tract characterized by delta was generated. Depositing fault zones near depression parts in front of the main lobe of delta distribute mainly lowstand sands, which are the main accumulation zones of lowstand sand reservoir and prospecting direction for exploring shelter reservoir.