柴达木盆地跃进二号油藏沉积相及平面展布

Sedimentary Facies and Planar Distribution of Yuejin No.2 Oil Reservior in Qaidam Basin

跃进二号油田含油层位包括下油砂山组(N21)、上干柴沟组(N1)和下干柴沟组下部(E31)三个主力油组。长期以来,一直认为它是一般的辫状河三角洲沉积,主要砂体类型为分流河道、河口坝和席状砂。笔者在研究过程中,通过岩心观察、测井相分析,并根据沉积物粒度、砂体空间展布规律和现代河流沉积模式类型,认为本区大的沉积背景仍然为辫状河三角洲,但沉积微相类型和砂体成因模式与一般辫状河三角洲不同,即骨架砂体以水下分流砂坝为特征,分流河道和河口坝欠发育。主力油组沉积时期,研究区湖盆水体浅,入湖水流在向湖推进过程中,流水动能强,分流河道主要起输送沉积物通道作用,沉积作用弱,而分流河道之间水体能量相对弱的区域沉积作用强,因而形成了以分流砂坝沉积为主的沉积特征,这种沉积模式打破了传统三角洲沉积以河道和河口坝沉积为主的相模式,建立了以土豆状散布于河道间的分流砂坝为格架的沉积微相新模式。

Yuejin No.2 oil reservoir includes three main oil groups：Xiayoushashan Formation（N21）,Shangganchaigou Formation（N1）,and the lower part of Xiaganchaigou Formation（E31）For a long period of time,it has been considered to be a general braided river delta,with the main types of sandstone being distributary channel,mouth bar,and sand sheet.In our study, through the core observation,log-phase analysis,and in accordance with the sediment grain size,sand body,and the spatial distribution patterns of modern river sediment type,the deposition background of the district is still braided river delta,but the sedimentary microfacies types and causes of sand body model are different from the general braided river delta,which is that the skeleton of sand body is characterized by diversion dams,diverting rivers,and estuaries due to dam development.In the period of main oil groups deposition,the basin is with shallow water,during the water flowing into the lake in advance,kinetic energy of flowing water is strong,diverting rivers play the role of transmission,resulting in a weak sedimentation;while the region among distributary channels with weak water energy has a strong sedimentation,creating a dam to divert sand deposition as mainly sedimentary characteristics.This depositional model broke the traditional delta sedimentary facies model dominated by river and dam and established a new sedimentary microfacies modell of a potato-shaped diversion dam spreading in the river.