断陷湖盆同生断层发育区三角洲砂体分布模式

Distribution pattern of deltaic sand bodies controlled by syn-depositional faults in a rift lacustrine basin

以东营凹陷王43地区古近系沙河街组二段湖泊三角洲为例,综合应用岩心、测井、三维地震资料,从构造-沉积响应的角度探索断陷盆地复杂断块区同生断层控制的三角洲砂体沉积构型特征。复杂断块内低级序同生断层分布密集且具有不同倾向,沿同生断层走向活动性分布不均,进而控制了三角洲砂体的沉积过程。受同生断层活动的影响,三角洲分流河道易于从同生断层活动性较弱部位通过,并在同生断层活动性较强部位产生偏转或被限制。在单条同生断层下降盘或微地堑地区,砂体厚度增加,更易连片发育,垂向易形成多期连续型叠置样式。而在同生断层控制的地垒地区,砂体垂向上数量减少,发育间歇型叠置样式。本研究可以为复杂断块油田精细勘探开发地质研究提供新的研究思路和理论依据。

Take the lacustrine delta in the second member of Paleogene Shahejie Formation in block Wang43,Dongying sag,Bohai Bay Basin as an example,the deposition architectural characteristics of lacustrine deltaic sand bodies controlled by syn-depositional faults in complex fault blocks of rift basin are examined from the aspect of structure-deposition response,using cores,well logs and three-dimensional seismic data.The small-scale syn-depositional faults in complex fault blocks are dense and different in dip,the activity along the strike of syn-depositional fault varies in different positions,and all these control the sedimentary process of deltaic sand bodies.Influenced by syn-depositional faults,the deltaic distributary channel is more likely to pass through the position with weak fault activity,and be deflected or limited at the position with strong fault activity.In downthrown side of a single syn-depositional fault or micro-graben areas,sand bodies increase in thickness and planar scale,and sand bodies of multiple stages are likely to stack over each other vertically.In micro-horst areas controlled by syn-depositional faults,the sand bodies decreases in number,and appear in intermittent superimposed pattern vertically.This study can provide new research ideas and theoretical basis for exploration and development geological research of complex fault block oilfields.