柴达木盆地英东油田N_2~2和N_2~1砂岩储层特征

柴达木盆地英东油田N22和N21砂岩储层具有层数多、单层厚度薄、粒度细的特点,油气分布与储层性质密切相关。根据岩心、铸体薄片、扫描电镜、压汞、X射线衍射等资料,对英东油田碎屑岩储层特征及控制因素作了系统研究。结果表明：①储层主要为细—粉粒岩屑长石砂岩,成分成熟度中等,结构成熟度高,杂基含量低,胶结物以方解石为主,含量中等,成岩作用整体较弱。②储集空间以原生粒间孔占绝对优势,含少量溶蚀孔及粒内裂隙孔,孔隙结构类型主要为中孔-中喉型、大孔-中喉型和大孔-粗喉型。③埋藏浅是研究区优质储层发育的重要前提,沉积微相、原始组构及胶结物含量控制着储层物性差异;压实作用是储层减孔的主控因素,其次为方解石胶结作用。④研究区储层可划分为4类,其中Ⅰ类、Ⅱ类和Ⅲ类储层为有效储层,Ⅳ类储层为无效储层或需要利用改造措施加以改造的储层。根据该区储层特征总结出＂有砂即储＂的规律,并指出其油气勘探的重点在于寻找有利相带及砂体。

Reservoir characteristics of N2^2and N2^1 in Yingdong Oilfield, Qaidam Basin

The sandstone reservoirs of N2^2 and N2^1 in Yingdong Oilfield are characterized by much and thin layers and fine-grained, which play an important part on hydrocarbon distribution. Based on core, thin section, scanning electron microscope, mercury penetration and X-ray diffraction, reservoir characteristics and main controlling factors of N2^2 and N2^1 sandstones in Yingdong Oilfield were systematically studied. The result shows that： （1）N2^2 and N2^1 sandstones are lithic arkose, mainly of fine-grained sandstone and sihstone, with medium compositional maturity and high textural maturity. Matrix content is low, and as the main type of cement, calcite content is moderate. Diagenesis of the sandstone reservoir is weak. （2）The main reservoir space is primary intergranular pore, followed by dissolved pores and intragranular crack. Pore structure of reservoir includes three major types： medium pore and throat, large pore and medium throat, large pore and coarse throat. （3）High quality reservoir in the study area is attributed to shallow burial condition. Microfacies, sandstone texture and cement content are key factors to distinguish good porosity and permeability sandstone. Compaction is the main factor for porosity-losing processes, and calcite cementation comes next. （3）The reservoir in Yingdong Oilfield can be subdivided into four classes, and class I , II and m are commercial, while Class IV is noncommercialand requiring improvements. It is suggested that while there is sandstone there is reservoir, and the key of exploration is searching sedimentary facies of high quality.