柴达木盆地扎哈泉地区致密油新类型的发现及其特征

运用沉积学、储层地质学和有机地球化学等手段,对最近在柴达木盆地扎哈泉地区新发现的致密油藏进行研究。扎哈泉地区沉积相以滨浅湖的滩坝砂为主体,为致密油的形成打下了沉积学基础。本区致密油的产状特征是油层薄,与烃源岩呈薄互层产出,为近源自生自储关系,提供了非常有利于致密油形成的源储共生组合条件。致密油储层致密,具有微米级孔隙和纳米级孔隙,储层平均孔隙度为5.8%,平均渗透率为0.45m D,属于典型致密油藏。与致密油储层互层的古近系烃源岩的有机质类型以Ⅰ型和Ⅱ1型为主;Tmax在311~461oC之间,处于低熟至成熟阶段。有机碳含量主要分布在0.29%~4.42%之间,但多数低于1.0%,比现阶段致密油烃源岩的标准明显偏低,属于一种特殊类型。与其他盆地相比,虽然柴达木盆地扎哈泉地区致密油烃源岩有机质丰度偏低,但该地区咸化湖泊环境使其具有生烃转化率高的典型特点,因此,同样可以生成较多的液态烃类,预示柴达木盆地致密油勘探具有很大的潜力。

A New Type of Tight-Oil and Its Feature in Zhahaquan Area of Qaidam Basin

Sedimentology, reservoir geology and organic geochemistry are applied to the research of tight-oil found in Zhahaquan area of Qaidam Basin. The sedimentary facies in Zhahaquan area are mainly beach-bar sand, which becomes a good sedimentary background for tight-oil forming. The occurrence of tight-oil in this area is thin oil layer and source rocks interbed, so the tight-oil is a self-generating and self-preserving reservoir near source. Which provides a favorable condition of reservoir and source paragenesis for tight-oil forming. The reservoir is very tight which has pore of micron and nanometer, and has an average porosity of 5.8% and an average permeability of 0.45 mD, so it is a typical tight-oil reservoir. Type of organic matter in Eocene source rocks is mainlyⅠandⅡ1.Tmax value is 311?461oC, which illustrates that the source rocks are between immaturate and maturation stages. Content of organic carbon falls 0.29%?4.42%, mainly less than 1.0%, which is much less than the source rock indicator for tight-oil. The tight-oil in the area should be a new type. It is believed that the conversion efficiency of the organic matter is higher in the lake environment with high salinization in this area, although the abundance of organic matter in source rock of tight-oil in Zhahaquan area of Qaidam Basin is much less than that in other basins. Therefore, the environment here can also support formation of much liquid hydrocarbon, and there is a good potential of tight-oil exploration in Qaidam Basin.