松辽盆地徐家围子断陷沙河子组物源与沉积体系分析

Provenance and Sedimentary System Analysis of the Shahezi Formation in the Xujiaweizi Fault Depression,Songliao Basin

沙河子组是松辽盆地北部深层重要的天然气勘探目的层,复杂多变的物源体系制约了研究区沉积体系刻画和致密气储层预测。综合碎屑岩骨架矿物、砾石成分、重矿物组合和地震反射特征分析,对沙河子组母岩性质和物源方向进行系统研究。结果表明:1)徐家围子断陷沙河子组可分为安达凸起、中央古隆起、徐东斜坡三大物源区和安达、徐西、宋站、徐东四个物源体系;2)不同物源体系的物源方向存在差异,其中安达地区受西北安达凸起物源影响,物源方向以南西向、东西向为主;徐西凹陷受西部中央古隆起物源影响,物源方向以东西向为主;宋站地区和徐东凹陷受东部徐东斜坡物源影响,物源方向以东西向、北东向为主;3)断裂活动影响沉积物充填方式、物源供给决定沉积相发育规模、地貌特征控制沉积体延伸方向,断裂、物源和地貌特征的联合作用,造成断陷西侧陡坡带安达和徐西物源体系以扇三角洲沉积为主,而东部斜坡区宋站和徐东物源体系则主要发育辫状河三角洲。

The Shahezi formation is one of the most important exploration targets in the northern Songliao Basin,where complicated and shifting provenance severely restricts the study of sedimentary systems and the forecast of tight gas reservoirs.We check the properties of the parent rock and provenance direction system,based on the data for the mineral composition of clasolite,conglomerate component,combination of heavy minerals,and seismic reflection features.The result is that there are three provenances,such as the Anda uplift in southwest,paleo-central uplift in the west,and Xudong slope in the east,and the parent rock properties are different from each other.The sedimentary facies in the Anda area are influenced by the Anda uplift in the southwest,while the source direction is mainly south-west to northeast and west to east.The provenance of the Xuxi Sag is mainly from the paleo-central uplift in the west,and the source direction is west to east.The Songzhan area and Xudong sag are influenced by the Xudong slope in the east,and the source directions are mainly northeast to southwest and east to west.The sediments on the western side,which is the steep slope belt of the fault depression,are mainly fan-delta deposits,while sediments on the east gentle slope are mainly braided river delta deposits.The sedimentary system of the Shahezi Formation is a result of the union of fault activity,provenance,and geomorphic features,while the sediment filling system is influenced by fault activi-ty,sediment scale depends on the provenance supply,and sediment direction is determined by geomorphic features.