柯坪露头区柯坪塔格组河流作用为主的三角洲沉积特征及其油气勘探意义

Sedimentary features of fluvial-dominated delta in the Kepingtage Fm in Keping outcrop area and their significance for petroleum exploration

塔里木盆地志留系海相碎屑岩储层是一套重要的勘探目的层系,在塔中和塔北地区勘探已有突破。但有关这套储层的沉积环境和沉积特征还没有形成统一的认识,不利于下一步的勘探。通过野外露头精细沉积学观察及室内镜下分析,揭示柯坪露头区柯坪塔格组由3个三级层序构成,其内发育以大型河流作用为主的三角洲沉积,主要为三角洲前缘和前三角洲沉积,并进一步识别出水下分流河道、支流间湾、河口坝、远砂坝及前三角洲泥等沉积。同时,层序底界大型下切水下分流河道的发现,预示着深水区可能存在大型深水浊积砂体。柯坪塔格组该类三角洲沉积组合对塔里木盆地志留系碎屑岩油气勘探具有重要的指示意义,较好的油源条件、面状分布的砂体及多套储盖组合构成了较好的油气成藏条件,而其深水区可能存在的浊积砂体也是潜在的油气勘探区。

The Silurian marine clastic reservoir in Tarim Basin is an important exploration play,in which some exploration breakthrough has been made in Central Tarim and North Tarim.However,no consensus has been reached about its sedimentary environment and characteristics,influencing future exploration.Based on the outcrop research and microscopic analysis of thin sections,this paper reveals that the Kepingtage Formation（Fm）in the Keping outcrop area can be divided into three third-order sequences.Large-scale fluvial-dominated delta deposits（mainly delta front and pro-delta deposits）are recognized in the Kepingtage Fm.Further more,several microfacies such as underwater distributary channel,inter-branch channel bay,mouth bar,distal bar and pro-delta mudstone are identified.The existence of large incised channel on the lower boundary of sequence indicates that large-scale deep water turbidite sandbody may develop in deep water.This delta deposits combination in the study area is of great significance for petroleum exploration in the Silurian marine clastic reservoirs in Tarim Basin.Favorable source rock conditions,large sandbody and multiple reservoir-source rock combinations are favorable for hydrocarbon accumulation.The turbidite sandbodies possibly developed in the deep water area are also the potential exploration targets.