Abstract: In order to accelerate the exploration and development process of deep tight sandstone gas in the southern Songliao basin, the formation mechanism of tight sandstone reservoir and the main controlling factors of reservoir formation are studied. At present, the discovered deep tight gas can be divided into three types: Stable thick sandstone, sandstone-mudstone interbedding, and muddy wrapped sandstone according to the petrological characteristics of tight sandstone. The physical properties of the reservoir are generally poor, the main porosity is below 6%, and the main permeability is less than 0.10×10^-3 μm², which belong to ultra-low porosity and ultra-low permeability reservoir. Based on the mineral composition and microscopic characteristics of typical tight reservoirs, it is found that the formation of effective reservoirs of tight sandstone is mainly controlled by three factors: First, chlorite enclaves are developed in the early diagenetic stage, which effectively inhibit the occurrence of intergranular calcareous cementation and siliceous cementation during the middle and late diagenesis, and protect the original residual intergranular pores; Second, secondary pores are formed by the dissolution of volcanic rock debris; Third, hydrocarbon generation pressurization produces a large number of micro fractures, which improves the seepage characteristics of the reservoir. The controlling factors of tight sandstone gas reservoir formation  are summarized as followings, the sufficient gas source, the sandbody controlled by slope paleo-valley and fault, the reservoir controlled by secondary dissolution and microfracture, the enrichment controlled by fault activity and stable cap rock.

Key words: southern Songliao basin, deep tight sandstone gas; effective reservoir, main controlling factor of reservoir formation