河控型扇三角洲沉积特征及控制因素:以准噶尔盆地玛湖凹陷上乌尔禾组为例*

近年来对扇三角洲相带及沉积模式的研究有力地支撑了油气勘探大发现,因而扇三角洲类型细化研究受到越来越多的重视。依据23口井岩心资料、大量录测井资料、古地貌和地震等资料,分析了准噶尔盆地玛湖凹陷上乌尔禾组河控型扇三角洲沉积特征和控制因素。结果表明: (1)玛湖凹陷上乌尔禾组发育3大类、8亚类、23细类岩相类型,牵引流成因的岩相比例高,砾石间多为砂质充填或是半充填;(2)可分为辫状河道、碎屑流带、水下分流河道、河口坝等10个微相,以辫状河道与水下分流河道微相为主;(3)河控型扇三角洲平面形态多呈长轴扇形,玛湖凹陷上乌尔禾组发育中拐、克拉玛依、白碱滩、达巴松4个长轴形扇体;(4)河控型扇三角洲的沉积受潮湿气候和古地貌因素控制。在此基础上,建立了上乌尔禾组河控型扇三角洲沉积纵向相带序列模式和沉积模式,可为扇三角洲具体类型的判别以及类似盆地的油气勘探提供地质依据。

Sedimentary characteristics and controlling factors of river-dominated fan delta: a case study from the Upper Urho Formation in Mahu sag of Junggar Basin

In recent years,the study of fan-delta is helpful for the exploration of oil and gas,which attracts more attention on the detailed classification of fan-delta. The sedimentary characteristics and controlling factors of the river dominated fan-delta in the upper Urho Formation in Mahu sag of the Junggar basin is analyzed based on the core data from 23 wells,logging data,geomorphology and seismic data. There are 3 classes,8 subclasses and 22 types of lithofacies in the upper Urho Formation. Among them,the lithofacies linked to traction current takes a large proportion and the space between gravels and pebbles are filled or partly-filled by sandy grains. Ten types of microfacies such as braided channel,debris flow unit,subaqueous distributary channel and mouth bar are distinguished and the braided channel and subaqueous distributary channel are the dominated microfacies. The plane morphology of the river dominated fan-delta is usually fan shape with a high length-width ratio. There are four major fan-delta system named Zhongguai,Karamay,Baijiantan and Dabasong in Mahu sag. The sedimentation in the river dominated fan-delta is controlled by humid climate and paleo-geomorphology. According to paleoclimate and paleogeomorphology analysis of the Upper Urho Formation,the depositional sequence model of fan-delta in Mahu sag is established,which can provide the geological basis for the identification of microfacies in the fan delta and the petroleum exploration of similar sedimentary basins.