FORMATION AND DISTRIBUTION FEATURES OF LARGE-MEDIUM OIL-AND-GAS FIELDS IN MAIN FAULT DEPRESSIONS IN THE SONGLIAO BASIN

More than 30 Mesozoic fault depressions develop in the center of the Songliao Basin.The discovered large-medium oil-and-gas fields mainly locate in the petroleum-rich deep fault depressions named Xujiaweizi,Shiwu and Changling on the two sides of the NNE oriented Sunwu-Shuangliao lithospheric fracture in the center of the basin.Study of the petroleum generating geologic condition of deep fault depressions and the distribution characteristics of large-medium oil-and-gas fields shows that,large-medium oiland-gas fields mainly locate in the EW oriented inherited nose-like structures in the central fault horst zone,the gentle slope break zone,the gentle slope horst zone and the steep slope break zone around hydrocarbon generating center of half-graben deep faults and the lithospheric overlapping pinch and lithologic traps.The central uprising belts between two deep fault depressions are usually where large oil-and-gas fields can be found.The future exploration should be focused on the above-mentioned regions in deep fault depressions.