Abstract: The Permian Lucaogou Formation in the Junggar Basin is one of the oldest continental shale systems with liquid hydrocarbons in China. It contains diamictite deposits in a paralic salty lake basin, with abundant tight oil and shale oil resources. The Jimsar sag is a typical example with rich liquid hydrocarbons in eastern Junggar Basin. The analysis of actual geologic data of shale systems shows that the Lucaogou shale system has two petroleum systems (upper and lower) characterized by continuous hydrocarbon accumulation in thick self-sourced reservoirs composed of thin interlayers. First, the Lucaogou Formation was deposited in a paralic lacustrine environment, where intermittent seawater invasion caused mass organism die-off, making it possible to accumulate and preserve abundant organic matters. This formation is chiefly composed of fine-grained diamictite deposits, and can be subdivided into 2.5 tertiary sedimentary cycles in 6 layers. Second, the source rocks, with major lithologies of carbonate mudstone and siliceous mudstone, concentrate in the second and fifth members of the Lucaogou Formation (P₂l₂ and P₂l₅). Their TOC contents are mostly higher than 4% and the kerogen is mainly of Type Ⅱ. Their R_o values range between 0.6% and 1.1%, which indicates that they are within oil generation window. Third, the reservoir rocks are generally tight and comprised of carbonate rocks, carbonate sandstone and siliceous sandstone, with the porosity mostly of 6%-12% and the air permeability less than 0.1mD. The pore space is mainly composed of intragranular pores and intergranular dissolved pores which are connected by pore throats with the diameter from dozens of nanometers to hundreds of nanometers. The oil saturation generally ranges between 80% and 90%, thus the oil storage condition is better. And fourth, the formation fluid pressure is normal or slightly abnormally high. The average crude density is 0.8971 g/cm³, and average viscosity at 50oC is 165.2 mPa·s; therefore, the crude oil is the product of low-medium thermal evolution. In stratigraphic conditions, the fluid flowability is poor. The Lucaogou Formation in the Jimsar sag has abundant tight oil and shale gas resources. According to the evaluation results, it has technically recoverable tight oil resources of 0.91×10⁸t, and P₂l₁ and P₂l₄ are the "sweet spot intervals" of tight oil, the sweet spot is mainly in the central sag. Moreover, it has technically recoverable shale oil resources of 1.10×10⁸t, and P₂l₂ and P₂l₅ are the "sweet spot intervals" of shale oil, the sweet spot is also chiefly in the central sag.

Key words: tight oil, shale oil, sweet spot, sweet spot interval, liquid-rich shale, unconventional petroleum, saline lacustrine, fine grain sediments, tight reservoirs