沉积学报2025，Vol.43Issue(6)：2168-2186,19.DOI:10.14027/j.issn.1000-0550.2024.017
内陆坳陷湖盆远岸砂质滩坝沉积模式
A Depositional Model of a Sandy Beach Bar on the Far Bank of an Inland Depression Lake Basin
摘要
Abstract
[Objective]In the Tainan region of Qinghai oil field,within the middle to upper strata of the Sebei Group,notable beach-bar sedimentary sand bodies form key high-quality reservoirs.The genesis and spatial distribu-tion of these beach-bar sands have long been debated,creating a bottleneck in further exploration and exploitation of the gas field.This scenario underscores an imperative need for in-depth characterization within the Tainan area's beach-bar structures.It's essential to precisely identify the various sedimentary microfacies and to construct an appro-priate beach-bar depositional model,which will significantly enhance our understanding and utilization of these vital geological resources.[Methods]Informed by the principles of sedimentology,this methodology takes into account the varying hydrodynamic conditions prevalent during the formation of beach-bar systems,which consequentially result in differing grain sizes and permeability of the sand bodies.By centering on the median grain size as a pivotal metric,we synthesize a log response template for lithofacies,thereby establishing refined standards and dynamic responses for well-log interpretations of sedimentary microfacies.This advanced approach facilitates a more nuanced and scien-tifically grounded delineation of beach-bar sedimentary microfacies.Leveraging insights from modern sedimentary an-alogues and through a meticulous analysis of sand bodies within regions of dense well networks,the study employs horizontal well and production data to validate the rationality of microfacies classifications.Acknowledging the multi-faceted genesis of beach-bars,influenced by a spectrum of environmental and geological factors,this research culmi-nates in the proposition of a sophisticated beach-bar depositional model tailored for inland rift lake basins.This model reflects a deep integration of complex formation processes and characteristics unique to such environments.[Results]In the Tainan region,nestled within the middle and upper stratifications of the Sebei Group,a remarkable differentia-tion of beach and bar subfacies emerges.These can be intricately divided into distinct microfacies,including the bar core,bar margin,beach core,and beach margin.The bar sands,strategically overlaid on the beach sands,distinctly orient perpendicular to the prevailing northwest winds.Their morphology is characterized by either lens-like or crescent shapes,stretching an impressive length of approximately 1 250 meters and spanning a width of around 250 meters.This results in a linear length-to-width correlation,approximately 5,a ratio that harmoniously aligns with modern sedimentary environments.The beach sands exhibit a seamless,contiguous spread,predominantly extending in a perpendicular fashion relative to the source direction.This pattern becomes particularly pronounced during periods of low water levels.In drawing parallels with the beach-bar deposits found in Tengiz Lake,there is a notable correspondence in the extension direction,distribution patterns,and the critical length-width ratios of the bar sands.This comparative analysis underscores the similarity in sedimentary processes across diverse geographical locales.Furthermore,the abundant supply of source materials lays a robust foundation for the genesis and evolution of these beach-bar structures.A confluence of multifaceted factors,including the nuances of ancient tectonics,the intricacies of paleogeography,the dynamics of ancient monsoons,and the variances in past water depths,collectively weave a complex tapestry that dictates the developmental scale,the morphological characteristics,and the precise geographic localization of these beach-bar formations.[Conclusions]A"shallow lake,wave modification,oblique-arrangement"depositional model for beach-bar systems is proposed,offering theoretical guidance for identifying beach-bar systems in inland rift lake basins.This model encapsulates the dynamic interplay of wind-driven waves and shallow lake environments in shaping the beach-bar structures,emphasizing the importance of understanding both the physical processes and the sedimentological context in these unique settings.This approach provides a comprehensive frame-work for analyzing and interpreting beach-bar systems within inland rift basins,enriching the understanding of their formation and distribution.关键词
台南地区/滩坝/粒度/沉积微相/形成机制/沉积模式Key words
Tainan area/beach-bar/grain size/sedimentary microfacies/formation mechanism/depositional model分类
天文与地球科学引用本文复制引用
LI JiaWei,XU ZhenHua,CHENG LiHua,YIN YanShu..内陆坳陷湖盆远岸砂质滩坝沉积模式[J].沉积学报,2025,43(6):2168-2186,19.基金项目
中国石油大学(北京)科研启动基金项目(2462023YJRC034)[Science Foundation of China University of Petroleum,Beijing,No.2462023YJRC034] （北京）
