四川盆地秋林地区侏罗系沙溪庙组二段河流相沉积特征及储集差异性分析

Sedimentary Characteristics of Fluvial Facies and Analysis of Reservoir Differences in the Second Member of Jurassic Shaximiao Formation in Qiulin Area,Sichuan Basin

为阐明四川盆地沙溪庙组河流相沉积特征及相同沉积背景下发育的砂体具有储集差异性的成因机理,首先,通过岩心沉积特征、钻井与地震数据,选取秋林地区侏罗系沙溪庙组二段开展沉积研究。其次,以Ⅳ号砂体和Ⅴ号砂体为例,结合区域地质背景,分别从母岩、沉积、成岩和构造4个角度分析储层差异性的主控因素。结果表明:研究区目的层段发育曲流河沉积,根据沉积构成差异,可划分为常规型曲流河和辫状型曲流河;沉积作用是造成研究区沙溪庙组二段储层差异性的主控因素,高孔高渗储层(Ⅳ号砂体)为辫状型曲流河沉积,中孔低渗储层(Ⅴ号砂体)为常规型曲流河沉积。最后,结合高分辨率层序地层学,可得知基准面旋回控制河型演化,进而影响储层差异。该项研究可为其他具有相似沉积背景的储层评价与预测等提供借鉴。

In order to delineate the sedimentary characteristics of fluvial facies and the mechanism of the reservoir differences developed in the same sedimentary background,firstly,the sedimentary characteristics of cores,drilling and seismic data were used to investigate the second member of Shaximiao Formation in Qiulin area as an example.Secondly,combined with the regional geological background,No.Ⅳand No.Ⅴsand bodies were taken as examples,the main factors influencing the reservoir differences were analyzed from the perspectives of parent rocks,sedimentation,diagenesis and tectonism.The results show that meandering river deposits generally develop in the second member of Shaximiao Formation in Qiulin area,and can be divided into two types:conventional meandering river deposits and braided meandering river deposits.Sedimentation is the main factor influencing reservoir difference in the second member of Shaximiao Formation,the reservoir with high porosity and high permeability(No.Ⅳsand body)is belonged to braided meandering river,while the reservoir with medium porosity and low permeability(No.Ⅴsand body)is belonged to conventional meandering river.Finally,combining with the high resolution sequence stratigraphy,the base-level cycle was concluded to control the evolution of the river patterns,thus affecting the reservoir difference.The study can provide reference for other reservoir evaluation and prediction with similar sedimentary background.