鄂尔多斯盆地陇东地区长9油层组储层沉积学特征

Characteristics of reservoir sedimentology of Chang 9 oil-bearing layer of Yanchang Formation in Longdong area, Ordos Basin,China

通过对36口井的岩心观察描述和108件样品的铸体薄片鉴定、扫描电镜、物性、孔隙结构分析的综合研究,表明鄂尔多斯盆地陇东地区三叠系延长组长9油层组属于浅水三角洲沉积体系,储集岩主要为三角洲平原水上和前缘水下分流河道微相的灰色中-细粒岩屑长石砂岩,储集空间以剩余原生粒间孔为主,次为粒间和粒内溶孔,少量铸模孔,喉道以中、细喉为主,储层物性中等略偏差,属中-低孔、低渗孔隙型储层。储层发育受沉积作用、砂体厚度和成岩作用复合控制,可划分为4类储层,有利于储层发育的沉积微相依次为水下分流河道、水上分流河道及河口坝砂体,好的Ⅰ、Ⅱ类储层主要发育于水下分流河道砂体中。

Based on the core observation of 36 wells and casting thin section, scanning electron microscope, physical property, pore structure and other comprehensive analyses of 108 samples, this paper studies Chang 9 sandstone reservoirs of Triassic Yanchang Formation in the Longdong area. The results show that there are develop the distributary channel and underwater distributary channel sandbodies of shallow-water deltas. The lithology is mainly gray medium-fine-grained lithic arkose sandstone. The space mainly includes primary remanent intergranular pores and intragranular dissolved pores. The major throats are medium-fine and fine. The reservoir properties are mainly worse. The reservoirs have medium-low permeability, and are mainly controlled by the deposition, sandbody thickness and diagenesis. The sedimentary facies control the distribution of reservoir sandbodies, and the compaction, cementation and dissolution control the pore structure and physical property. The reservoir sandstones of Chang 9 oil-bearing layer can be classified into four types. The most advantageous microfacies are distributary channels, underwater distributary channels and mouth bars of the shallow-water delta.