砂质辫状河岩相与构型特征--以山西大同盆地中侏罗统云冈组露头为例

摘要

砂质辫状河沉积具有极好的储集性能，是重要的油气储层。为了阐明砂质辫状河储层的岩相与构型特征，定量表征构型单元的几何属性和物性特征，采用露头实测、精细构型解释以及实验分析等方法对山西大同盆地中侏罗统云冈组砂质辫状河露头进行了系统研究，共识别出7种岩相类型和5种岩相组合。砂质辫状河中发育河道（ CH）、心滩（ CB）、边滩（ PB）、废弃河道（ ACH）及漫溢沉积（ OF）5种典型构型单元，以河道和心滩构型单元为主，两者的累积分布频率高达78％。河道构型单元的厚度介于2.5～6.5 m，宽厚比约为25～30，平均孔隙度为7.1％。心滩构型单元的厚度介于2.5～7.0 m，宽厚比约为30～35，平均孔隙度为7.8％。同一沉积时期，砂质辫状河中存在4种基本构型单元组合，分别为CH－OF，CH／ACH－PB，CH－CB－CH和CH／ACH－PB－OF。不同沉积时期的构型单元空间分布可表示为4种基本组合类型及河道构型单元在垂向和横向的重复或叠加。河道和心滩构型单元为砂质辫状河的主要储层类型，但心滩构型单元的规模和储层物性优于河道构型单元。%Sandy braided river deposits have excellent physical properties ,thus are important oil/gas reservoirs .In order to demonstrate the lithofacies and architectural characteristics of the sandy braided river reservoirs ,and quantify the geo-metric properties and physical properties of architectural units ,a systematic study for outcrops of sandy braided river de-posits in the Middle Jurassic Yungang Formation in the Datong Basin has been conducted on the basis of outcrop observa -tion,detailed interpretation of architectures ,and laboratory analysis.Seven types of lithofacies in five associations have been identified .Five typical architectural units were identified in the sandy braided river deposits , including channel ( CH) ,channel bar ( CB) ,point bar ( PB) ,abandoned channel ( ACH) ,and overflowing sediments ( OF) .Among these architectural units ,the channel and channel bar are the main architectural units with accumulative distribution frequency up to 78%.The thickness of channels ranges from 2.5 m to 6.5 m,width/thickness ratio is about 25 -30,and the average porosity is 7.1%.The thickness of channel bars ranges from 2.5 m to 7.0 m,width/thickness ratio is about 30-35 ,and the average porosity is 7.8%.During the same depositional period ,four basic combination types of the architec-tural units developed in the sandy braided river ,namely CH-OF,CH/ACH-PB,CH-CB-CH,and CH/ACH-PB-OF.The spatial distribution of the architectural units in the different depositional periods is characterized by superposition or repe -tition of these four basic combination types in vertical and lateral .Channel and channel bar are the major reservoir types in the sandy braided river deposits ,but the scale and physical properties of the later are better than the former .