鄂尔多斯盆地奥陶系颗粒滩白云岩储层特征及主控因素

Characteristics and Main Controlling Factors of Ordovician Grain Beach Dolomite Reservoir in Ordos Basin

基于岩心观察、薄片鉴定、物性分析和地球化学分析,结合岩相古地理研究,认为鄂尔多斯盆地中东部奥陶系盐下发育三套颗粒滩白云岩储层,分别为下奥陶统马家沟组马二段、马四段和马五_(7+9)亚段。马二段颗粒滩环台内洼地分布,马四段和马五_(7+9)亚段颗粒滩环台内洼地以及滩间次级洼地两侧的相对隆起带分布。白云岩储集空间类型主要为粒间孔、晶间(溶)孔、溶蚀孔洞和裂缝。三维CT分析表明,白云岩储层具有优良的储渗性能。颗粒滩白云岩主要为浅埋藏蒸发海水渗透回流交代成因。白云岩储层的发育主要受控于三个因素:层序格架控制的颗粒滩分布,表生岩溶作用,构造裂缝系统。

Based on the data from cores, thin-sections, porosity and permeability, and geochemistry, three sets of grain beach dolomite reservoirs were developed under the Ordovician gypsum salt in east-central Ordos Basin. They were the LowerOrdovician Majiagou Member-2, Member-4, and Submember-Sy＋g. According to the lithofacies palaeogeography, the grain beach usually distributed around the depression （Member-2） and the secondary depression （Submember-Sy＋g） in the platform, especially on the relative uplift belts. The types of dolomite reservoirs are mainly intergranular pores, intercrystalline pores, intercrystalline dissolution pores, dissolution pores and caves, and fractures. 3-D computed tomography shows that the dolomite reservoir has excellent porosity and permeability. The genesis of the grain beach dolomite is mainly the osmotic reflux of evaporative seawater in shallow burial diagenetic environment. The development of the dolomite reservoir is mainly controlled by three factors： the distribution ofthe grain beach under the sequence framework, the karstification, and the fracture system.