惠民凹陷大芦家地区馆陶组三段沉积微相类型及空间展布

Sedimentary Microfacies Types and Space Distribution of the Third Member of Guantao Formation in Dalujia Area of Huimin Sag

针对惠民凹陷大芦家地区各断块地层单元划分不一致,沉积相认识存在分歧等问题,依据旋回级次、旋回性质等,将馆陶组三段划分出2个四级旋回、4个五级旋回、16个六级旋回;并以岩芯及室内分析资料、测井资料等为主要依据,综合分析岩石类型、粒度及结构特征、垂向粒序变化、层理构造类型及自然电位曲线形态等。结果表明:惠民凹陷大芦家地区馆陶组三段主要发育冲积扇及辫状河;冲积扇主要发育辫流砂岛、辫流沟道、辫流带、漫流席状砂、远端砂丘等微相;辫状河主要发育心滩,辫状河道充填,天然堤、漫滩和道间洼地沉积,泛滥平原沉积,废弃河道等微相;2个四级旋回的沉积相类型及空间展布特征相似;第Ⅰ五级旋回在研究区中偏西部属冲积扇沉积,主要发育辫流砂岛、辫流沟道、辫流带微相,在东部属扇前平原沉积;第Ⅱ五级旋回早期以辫状河沉积为主,河道规模较大,仅在第Ⅱ1六级旋回的东北部位见冲积扇的辫流砂岛及辫流沟道微相;第Ⅱ五级旋回中期属辫状河沉积,河道规模减小,2个河道群自NW向SE方向流动;第Ⅱ五级旋回晚期河道规模更小,逐渐向曲流河沉积过渡。

On the issues of the inconsistent of stratigraphic division of blocks in the third member of Guantao Formation in Dalujia area of Huimin sag and the differences of understanding on sedimentary facies,according to the order and characteristics of cycle,the third member of Guantao Formation was divided into two forth-order cycles,five fifth-order cycles and sixteen sixth-order cycles;according to the core data,laboratory analysis,log information,etc.,rock type,particle size and textural characteristics,change of vertical particle size,type of bedding structure and shape of spontaneous potential curve were comprehensively analyzed.The results show that alluvial fan and braided river develop in the third member of Guantao Formation in Dalujia area of Huimin sag;for alluvial fan,the main microfacies types include braided stream sand island,braided stream channel,braided stream belt,overland flow sheet sand,distal sand dune,and so on;for braided river,the main microfacies include river island,braided channel filling,floodplain sedimentary,abandoned channel,and the sedimentary of natural levee,floodplain and interchannel mud,and so on;the sedimentary facies types and space distribution of two forth-order cycles are similar;the fifth-order cycle I in the middle-westward of the study area belongs to alluvial fan sedimentary,the microfacies including braided stream sand island,braided stream channel and braided stream belt develop,and the fifth-order cycle I in the eastern part belongs to fan front plain sedimentary;in the early of the fifth-order cycle Ⅱ,braided river sedimentary mainly develops,river channel is large,and the microfacies including braided stream sand island and braided stream channel develop only in the northeastern part of the sixth-order cycleⅡ1;in the middle of the fifth-order cycle Ⅱ,braided river develops,and river channel decreases,two river channel groups flow from NW to SE;in the late of the fifth-order cycleⅡ,river channel decreases further,and gradually transforms into meandering river sedimentary.