陕北地区上三叠统辫状河心滩微观特征

Microscopic characteristics of braided river barof Upper Triassic in Northern Shaanxi

鄂尔多斯盆地陕北地区上三叠统延长组以辫状河沉积为主,发育灰绿色、浅灰绿色砂岩、粉砂岩、灰绿色、浅灰黑色泥岩。为明确陕北地区辫状河心滩砂体微观特征,利用测井相特征、辫状河心滩规模分析心滩类别、发育特征、夹层类别及夹层分布特征。结果表明:陕北地区长2辫状河沉积发育纵向沙坝、横向沙坝、斜列沙坝3种类型心滩,辨析出心滩主体、滩头、滩尾、滩翼4部分;心滩内部夹层根据发育位置分为落淤层、串沟、坝间泥、道坝转换夹层4种类型,落淤层分为纵向落淤层、横向落淤层、斜列落淤层3种类型;心滩发育规模是预测落淤层分布的首要因素,对心滩位置的精准识别,结合心滩长宽比、宽厚比绘制心滩规模平面分布模型,预测井间落淤层分布特征。辫状河心滩微观特征研究是分析辫状河沉积的首要任务,心滩内部夹层发育特征是影响辫状河储层的重要因素,研究成果对辫状河心滩砂体特征研究提供借鉴作用。

The Upper Triassic Yanchang Formation in the Qingpingchuan area of the northern Shaanxi slope of the Ordos Basin is dominated by braided river deposits, with grayish green and light grayish green sandstones, siltstones, grayish green and light grayish black mudstones with plant fossils.In order to clarify the microscopic characteristics of braided river bar sand bodies in Qingpingchuan area, the types, development characteristics, interlayer types and interlayer distribution characteristics of the bar are analyzed by using logging facies characteristics, braided river bar scale.The results show that the Chang 2 braided river in Qingpingchuan area developed three types of bar: longitudinal bar, transverse bar and oblique bar, and the four parts of bar body, beach head, beach tail and beach wing can be distinguished.According to the development position, the interlayer in the bar can be divided into four types: silting layer, cross ditch, mud between dams, and channel dam transition interlayer.The silting layer can be divided into three types: longitudinal silting layer, transverse silting layer, and oblique silting layer.And the development scale of the center beach is the primary factor to predict the distribution of the siltation layer.Through the accurate identification of the location of the center beach and the comparison of the length width ratio and the width thickness ratio of the center beach, the plane distribution model of the center beach scale is completed to predict the distribution characteristics of the siltation layer between wells.The research on the microscopic characteristics of braided river bar is the first step to analyze the braided river sand body deposition.The development characteristics of the interlayer in the bar is an important factor affecting the braided river sedimentary reservoir.The research results provide a reference for characterizing the braided river bar sand body.