黄骅坳陷板桥地区湖相滩坝砂体内部隔（夹）层成因机制与分布样式

摘要

黄骅坳陷板桥地区古近系沙河街组沙二段具有典型的湖泊滩坝沉积特点，其砂体内部主要发育泥质、钙质和致密粉砂质3种类型的隔夹层。利用构型分析法，将滩坝砂体分为复合坝、单一坝和坝内增生体3个构型要素，将内部隔（夹）层分为单一坝间隔层和单一坝内夹层2个级别。单一坝间隔层具有3种成因机制：（1）基准面波动造成单一坝叠置区分布的细粒沉积；（2）风暴作用形成的滞留泥砾沉积；（3）坝后水动力低能区域形成的泥质沉积。单一坝内夹层则是波浪能量衰减形成的细粒沉积，岩性以粉砂质泥岩、泥质粉砂岩为主。通过分析夹层的井上识别特征，结合青海湖、岱海现代沉积的原型地质模式，对单一坝进行内部构型解剖。结果表明，夹层厚度为0.1～1m，靠近岸线近水平分布，向湖中心方向以低角度倾斜，倾角为2°～5°。不同级次与成因的隔（夹）层在滩坝砂体中都有特定的发育部位，其分布规律和空间配置关系不仅可以反映不同隔（夹）层的沉积时间顺序，还可以依此来推测滩坝的沉积规模与展布形态。隔（夹）层会导致含油气性的差异，认识隔（夹）层分布规律是提高滩坝储集层油气采收率的关键。%The Member 2 of Paleogene Shahejie Formation in Banqiao area of Huanghua Depression developed typical lacustrine beach-bar deposits with three kinds of inter (inner)-layer in sand bodies, i.e.,muddy,calcareous and compact silty inter (inner)-layer.The beach-bar sand bodies can be divid-ed into three architecture elements using the reservoir architecture analytical method:Compound bar,sin-gle bar,and the inner accretion of single bar.The inter (inner)-layers in the beach-bar reservoir can be subdivided into two hierarchieInter-layer between single bars and inner-layer in single bar.There are three genetic mechanisms of inter-layer between single bar①Fine-grained sediments developed in a re-gion superimposed by two-phase single bars sand bodies caused by base-level change;②Retention mud-gravels drawn by storm activities;③Mud deposit in a low wave energy behind bars.The fine-grained in-ner-layers in single bar are formed by the attenuation of wave energy, and mainly consists of silty mud-stone and argillaceous siltstone.Further research is to dissect architecture inner single bar through well-log facies recognition and modern beach-bar prototype geological models in Qinghai Lake and Daihai Lake.It is found that the muddy inner-layers in single bar with thickness about 0.1~1m are nearly horizontal close lakeshore and inclines in low angle towards the center of the lake,with 2°~5°dip angle.Each hierarchy and genetic inter (inner)-layer is found in a certain region in a single bar sand body.The relative posi-tion and distribution pattern of each inter (inner)-layer can not only reflects the order of deposition in a single bar,but also be used to predict the scale and morphology of beach-bar.The inter (inner)-layers can lead to the diversity of oil-bearing properties,therefore it is important to reveal the distribution of inter (inner)-layers in beach-bar reservoirs,which is the key to raise oil and gas recovery ratio.