陆相湖盆坳陷期源-汇系统的要素特征及耦合关系--以南苏丹Melut盆地北部坳陷新近系Jimidi组为例

Element feature and coupling model of source-to-sink system in depression lacustrine basin:A case study of Neogene Jimidi Formation in Melut Basin,South Sudan

源—汇系统要素特征与耦合关系分析作为当前沉积学领域的研究热点,已成为定量预测沉积体及油气储集体规模的重要思路与手段之一。为了研究Melut盆地新近系Jimidi组沉积期的源—汇系统要素及其耦合关系,开展了钻测井资料分析、高分辨连片三维地震资料和盆缘区二维地震资料解释、表征了各源—汇要素之间的相关性。结果表明:①Melut盆地北部坳陷基岩岩石类型为前寒武系千枚岩和花岗片麻岩,Jimidi组沉积时期发育3个一级汇水单元,存在V型、U型、W型下切谷型以及断槽型四种搬运通道类型。②研究区可划分出3个源—汇系统,其中西北部Kaka—Ruman源汇系统为典型的斜坡型源—汇耦合模式,汇水区发育面积约600 km^(2)的河流-浅水三角洲沉积体系,东北部的Gandool—Wengi源—汇系统和西南部的Tean—Ruman West源—汇系统具有断裂坡折型源—汇系统的特征,盆内分别发育面积约400 km^(2)和112 km^(2)的扇三角洲沉积体系。③研究区源—汇系统要素定量分析显示,湖盆坳陷期盆内沉积物总量与源区汇水面积、地形高差、搬运通道截面积密切相关,汇水单元面积是决定沉积体系规模的首要影响因素,汇水单元面积大,则易于形成大规模沉积体系。该研究成果可预测Melut盆地Ruman地区Jimidi组的物源方向、沉积体系类型以及有利储集砂体展布,对下一步勘探部署具有指导作用。

Characteristics of elements in source-to-sink system and their coupling relationships,as one of the most important method for quantitative prediction in sediments and oil/gas reservoirs,have become the research hotspots in sedimentology.In order to characterize the elements feature and coupling relationships of source-to-sink system during the deposition of Neogene Jimidi Formation in Melut Basin,well drilling and logging data analysis,and interpretation of high-resolution 3D seismic data and 2D seismic data in the basin margins were carried out,and the elements of the source-to-sink system for depression lacustrine basin were characterized.The results show that:①The basement in the north depression of Melut Basin was dominated by Precambrian metamorphic rocks(phyllite)and granitic gneiss.Three first-level catchments were developed in the study area during the deposition of Jimidi Formation,four types of transportation pathways,V-type,U-type,W-type and fault trough type,were found.②Three source-to-sink systems can be divided:Kaka-Ruman source-to-sink system in the northwest was the typical slope-type source-to-sink coupling model,where the river-shallow delta depositional system of 600 m^(2) was developed in the catchment;Gandool-Wengi source-to-sink system in the northeast and TeanRuman West source-to-sink system in the southwest were characterized by fault-slope-break,where fan deltas of 400 km^(2) and 112 km^(2) were developed respectively.③The quantitative analysis for elements of the source-tosink systems in the study area showed that the total sediments inside the basin were closely relevant with area of catchments in the source area,topographic height difference and cross-sectional area of the transport channel during the depression stage in the lacustrine basins.The area of catchments was the primary influencing factor for the scales of depositional systems,and large catchments were favorable for the development of large depositional systems.Based on the results,types of depositional system and direction of sediments source for Jimidi Formation in Ruman area of Melut Basin have been confirmed and the distribution of favorable reservoir sandbodies have been predicted,which will guide the exploration deployment effectively.