The major basins of central-western China are rich in tight (sandstone) oil and gas deposits

which are the key exploration and development targets of the petroleum industry.However

the formation and distribution of these resources are complex and has put economic restrictions on their extraction.One way to solve this problem is to evaluate

screen and exploit "sweet spots" (promising reservoirs) to reduce uncertainties.Based on a characterization of tight oil and gas in clastic sequences of these basins

this study focused on classifying sweet spots by analyzing geological factors that controlled the formation and distribution of the sweet spots and by taking into consideration the applicability of prediction technologies to field data

a relative consistency between forming mechanisms and distribution patterns

and an integration of economic and technical strategies.The sweet spots were generally classified into the lithofacies-restrained

fracture-dominated

and unconformity-regulated types.Of which

the lithofacies-restrained sweet spots were controlled by diagenesis during burial and developed inside certain lithofacies; the fracture-dominated sweet spots were controlled by fracture networks and mainly formed in faults and folds with strong structural-deformation; and the unconformity-regulated sweet spots were controlled by leaching layers inside weathering crust and formed during long-term uplifting and strong weathering.The Jurassic "narrow channel" in the east slope of the West Sichuan Depression

the Xujiahe "fault-fractured complex" in Malubei area of northern Sichuan Basin

and the Carboniferous System in Chepaizi area of western Junggar Basin were selected to respectively analyze the formation

distribution and controlling factors of the three types of sweet spots.The results show that the classification by reservoir-forming geological processes and products is helpful for further studying the sweet spots and formulating more suitable geological

geophysical and engineering strategies to better evaluate

optimize and develop the sweet spots.