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近年来,柴达木盆地英西地区深层E_3~2油气勘探获得了重要发现。基于岩心观察、系统的微观岩石学、结构构造分析以及地球化学分析,研究柴达木盆地英西地区白云岩储集层特征及发育的主控因素。泥晶白云岩为英西地区E_3~2的主要有效储集岩,具有“低孔—特低渗”的物性特征,储集空间类型以白云石晶间孔为主,含部分微裂缝,这类孔径较小而数量极多的晶间孔储油是英西地区油藏稳产的重要控制因素。储层地球化学特征研究结果显示,白云岩储层为成化条件下的准同生交代成因类型,主要证据包括:①微观孔隙结构特征;②高Ca/Mg摩尔比值的非理想状态的成分组成;③“低锰”的元素地球化学特征;④“碳偏负氧偏正”的同位素地球化学特征及其反映的低温成因;⑤成核结晶速度较快的不稳定环境造成的低有序度结构特征。这类特殊成化环境下因晶格内部离子交换造成体积变化形成的收缩晶间孔,其孔径大小受控于当时的Mg~(2+)丰度,进而决定着储集层的物性,且这类晶间孔具有较强的抗压实能力,在深层、超深层依然能保存完好。准同生交代成因模式决定了白云岩在平面上分布广泛,因此这一研究成果在平面展布上和纵向深度上均拓展了柴西地区湖相白云岩勘探新领域。
In recent years, important discoveries have been made in deep E_3 ~ 2 oil and gas exploration in the western and western parts of the Qaidam basin. Based on core observations, systematic micro-petrology, structural tectonics and geochemical analyzes, the main dolomite reservoir characteristics and developmental controlling factors in the western and western Qaidam basin are studied. The dolomite dolomite is the main effective reservoir rock of E_3 ~ 2 in the western and western regions, and has the characteristics of “low porosity-ultra low permeability”. The type of reservoir space is dominated by dolomite intergranular pores with some microcracks The smaller pore size and the larger number of intercrystalline pore oil reservoirs are important controlling factors for stable oil production in western and western regions. The geochemical characteristics of the reservoirs show that the dolomite reservoirs are the genesis of the quasi-homologous metasomatism under the conditions of metamorphism. The main evidences include: (1) the microscopic pore structure characteristics; (2) the composition of non-ideal components with high Ca / Mg molar ratio ; ③ The elemental geochemical characteristics of “low manganese”; ④ The isotope geochemical characteristics of “carbon partial oxygen partial positive” and its reflection of low temperature genesis; ⑤ The unstable environment with high nucleation and crystallization speed Low degree of order structural features. The pore size of the shrinkage intergranular pore formed by the volume change caused by the ion exchange in the lattice in this kind of special formation environment is controlled by the abundance of Mg 2+ at that time and further determines the physical properties of the reservoir, Such intercrystalline pores have a strong anti-compaction ability, in the deep, ultra deep layer can still be preserved intact. The genesis of quasi-simultaneous generation determines that the dolomite is widely distributed in the plane. Therefore, this research result expands the new exploration area of lacustrine dolomites in the western Qaidam basin both in the plane distribution and in the longitudinal depth.