Abstract: The Carboniferous-Permian in Gubei area is relatively less eroded away compared to other areas in Jiyang exploration area, which has favorable self-generating and self-reserving coal-formed conditions. The Permian reservoir rock is dominated by gritstone and pebbled gritstone with quarter minerals. The storage space of reservoir occurs in primary intergranular pore, secondary pore, intercrystal micro-pore and fracture, dominated by secondary pore and fracture, belonging to low-porosity and low-permeability reservoir. The Upper Shihezi formation is of the best reservoir quality, while the Shanxi formation is of the poorest one of the Permian. And sedimentation, diagenesis and tectonization are the three factors controlling the reservoir quality, of which tectonization is the main controlling factor. The Permian reservoir in Gubei area is divided into four types for evaluation. The results indicate that the Upper Shihezi and the Lower Shihezi reservoirs belong to high-quality ones of type I and type II, and Gu-3 Wellblock in Gubei area is a central area for petroleum reservoir.

Key words: coal-formed gas, Permian, Gubei area, reservoir characteristic, secondary pore