湖盆浅水三角洲河道砂体定量表征与控制因素探究及霸县凹陷实例^*

Quantitative characterization and analysis of controlling factors of channel sand bodies of shallow-water deltas in lacustrine basins, and an example from Baxian sag,Bohai Bay Basin,China

摘要

浅水三角洲是含油气盆地中的重要储集层,河道砂体定量表征是高效勘探开发油气资源的基础。本研究定量测量9个现代三角洲的分支河道形态学参数,提出基于分支河道形态学差异可将三角洲分为伸长状、枝状与网状3类,供给沉积物粒度细、低砂地比利于伸长状分支河道形成,供给沉积物粒度中等、砂地比中等、高河流流量利于形成枝状分支河道,供给沉积物粒度相对粗、砂地比高、相对低河流流量利于网状分支河道形成。浅水湖盆背景下形成的霸县凹陷文安斜坡沙河街组一段(简称“沙一段”)浅水三角洲平原砂地比中等(0.34)、河流流量最强,形成枝状分支河道; 内前缘砂地比高(0.51)、河流流量较平原降低,形成网状分支河道。调研7个不同构造背景与供源体系的野外露头,挖掘其定量参数,数据表明供源体系与盆地类型控制河道规模,断陷湖盆扇三角洲分支河道规模最小,坳陷湖盆曲流河/辫状河三角洲分支河道砂体规模最大,分支河道与水下分支河道的厚度与宽度之间呈指数关系,由于外前缘水动力更为复杂,形成的水下分支河道砂体宽深比较平原、内前缘分支河道范围更广; 应用该定量关系得出霸县凹陷文安斜坡沙一段浅水三角洲平原分支河道宽度介于35.5~218.8 m之间,内前缘分支河道宽度介于25.1~138.1 m之间,外前缘水下分支河道宽度介于46.7~235.7 m之间,未受到湖浪等改造而呈现“席状化”的表现。期望以现代沉积和野外露头为基础,建立可适用于地下沉积区定量表征的三角洲河道砂体发育模型,为油气勘探与开发提供依据。

Abstract

Shallow water delta is an important reservoir in hydrocarbon bearing basins. Quantitative characterization of channel sand bodies is the basis for efficient exploration and development of oil and gas resources. In this paper,the morphological parameters of distributary channels in nine modern deltas are quantitatively measured. Based on the morphological differences of distributary channels,the deltas can be divided into three types: elongated,branched and reticular. Fine grained sediments and low sand ratio are conducive to the formation of elongated distributary channels. Medium grained sediments,medium sand ratio and high river discharge are conducive to the formation of branched distributary channels. Coarse grained sediments,high sand ratio and relatively low river discharge are conducive to the formation of reticular distributary channels. The shallow-water delta plain of the first member of the Shahejie Formation in the Wen’an slope of the Baxian sag,developed under a shallow-water lacustrine basin background,exhibits a moderate sand ratio(0.34)and the strongest river flow,forming branched distributary channels. In contrast,the inner front has a higher sand ratio(0.51)and lower river energy,resulting in reticular distributary channels. The seven field outcrops of different tectonic backgrounds and source systems were investigated to extract their quantitative parameters. The data show that the source system and basin type control the scale of distributary channels. The scale of the fan delta distributary channel in the rift lacustrine basin is the smallest,and the scale of the meandering river/braided river delta distributary channel in the post-rift lacustrine basin is the largest. The thickness and width of distributary channels and their terminal branches follow an exponential relationship. Due to more complex hydrodynamic conditions in the outer front,the terminal distributary channel sand bodies are wider and thicker than those in the plain and inner front. Based on this quantitative relationship,in the study area the widths of distributary channels in shallow-water delta plain are estimated to range from 35.5 to 218.8 m,while those in the inner front range from 25.1 to 138.1 m,and the terminal distributary channels in the outer front range from 46.7 to 235.7 m,showing “sheeting” features modified by lake waves. This study aims to establish a delta channel sand body model for quantitative subsurface characterization, integrating modern and outcrop analogs, and to provide a foundation for oil and gas exploration.

关键词

浅水三角洲 / 沉积特征 / 定量表征 / 控制因素 / 霸县凹陷 / 沙河街组 / 沙一段

Key words

shallow-water delta / sedimentary characteristics / quantitative characterization / controlling factors / Baxian sag / Shahejie Formation / First Member of Shahejie Formation

基金资助

*国家自然科学基金项目(编号: 42272110)资助