苏里格气田苏6区块盒8段古河道砂体演化规律

Evolutionary process of palaeochannel sandbodies of the 8^(th) member of Shihezi Formation in Block Su6,Sulige Gasfield

苏6区块盒8段是鄂尔多斯盆地苏里格气田主力产气层,但其沉积特征和砂体演化规律有待明确。分析岩性、沉积构造和旋回特征等沉积相标志,认为研究区目的层为河流相沉积,盒8下亚段为辫状河沉积,发育心滩、辫状河道、河漫滩和溢岸微相;盒8上亚段为曲流河沉积,发育边滩、废弃河道、河漫滩和溢岸微相。根据自然伽马测井曲线的多期正旋回特征和切割程度差异,将研究区目的层的正旋回叠置类型细分为加积叠加-强切割式、加积叠加-中切割式、退积叠加-中切割式和退积叠加-弱切割式4类,据此正旋回特征的差异,利用旋回和分级控制的对比方法,自下而上将盒8下亚段细分为2套小层6个单层,将盒8上亚段细分为2套小层4个单层。在此基础上,通过对单期河道的识别和河道构型要素的提取,将研究区河道砂体演化过程分为10期4个阶段,其中1—3期为砾石质辫状河演化阶段,4—6期为砂质辫状河演化阶段,7—8期为砾石质曲流河演化阶段,9—10期为砂质曲流河演化阶段。

The 8^th member of Shihezi Formation in Block Su6 of Sulige gas field is the main gas-producing strata of the Su?lige gas field in the Ordos Basin.However,the understandings on the sedimentary characteristics have long been controver?sial and the cognition for evolution of sandbodies have remained unclear.Based on the data of rock lithology,sedimentary architecture,cycle characteristics and other sedimentary facies indicators,the 8^th member of Shihezi Formation in Block Su6 belongs to the fluvial sedimentary facie.Furthermore,works have been made to that the lower 8^th member of Shihezi Formation is the braided river facies in which microfacies of central bar,braided channel,floodplain and overbank develop;while the upper 8^th member is the meandering river facies in which marginal bar,abandoned channel,floodplain and over?bank develop.According to the characteristics of multistage positive cycle of natural gamma logging curve and the differ?ence in incision degree,the positive cycle superposition in the target layer of the study area can be subdivided into 4 types:aggradation superposition-strong incision,aggradation superposition-medium incision,retrogradation superposition-medi?um incision and retrogradation superposition-poor incision.According to the difference of positive cycle characteristics and a comparison method based on cyclic and hierarchical control,the lower 8^th member can be subdivided into 2 sets of sub-zone and 6 sets of single layer from bottom to up,while the upper 8^th member can be subdivided into 2 sets of subzone and 4 sets of single layer.On this basis,through the identification of single channel and the extraction of channel architecture ele?ments,the evolutionary process of channel sand body in the study area was divided into 10 periods and 4 stages.The 1st,2nd and 3rd periods mark the evolution of the pebbly braided river;the 4th,5th and 6th periods indicate the evolution of the sandy braided channel;the 7th and 8^th periods correspond to the evolution of the pebbly meandering channel,and the 9th and 10th periods are characterized by the evolution of sandy meandering channel.