Distribution and characteristics of lacustrine tight oil reservoirs in China

摘要

Lacustrine tight oil resources in China are significant exploration targets, similar to the marine tight oil resources in North America, while there are clear differences in terms of the forming environment, as well as reservoir properties of these two systems. In this study, the geological characteristics of lacustrine tight rocks are discussed, including the distribution, petrology, storage space, and movable fluid saturation. The tight rocks are consisted of tight sandstone, tight carbonate rock, tight peperite, and tight sedimentary tuff, in which inter-granular pores and dissolved pores with the dimensions of 30-900 nm are mainly dominated by the storage space. The oil saturation typically exceeds 50% and the oil mobility is basically controlled by pore-throats with diameter less than 1 mu m. These four types of reservoirs show different potentials for tight oil, in which tight sandstone plays in the Ordos Basin and the Songliao Basin are taken as the preferred targets into account for exploration and development. Although the distribution area, physical properties, and mobility of lacustrine tight oil in China are not as good as those of tight oil in North America, the lacustrine reservoirs are often stacked in multiple layers, resulting in a great thickness, and possess relatively high oil saturation, making them pro-ducible and commercially viable. Fluid properties are critical to effectively recovery of tight oil, and more comprehensive geological evaluation on fluid mobility should be undertaken.