Abstract:To study the oil and gas distribution regularities of downward migration in petroleumbearing basin , based on the correlation of oil and gas flowing backward migration and conventional oil and gas migration, we mainly researched the forming conditions of oil and gas flowing backward migration and distribution area forecasting method. It turned out that according to the direction of transportation, the oil and gas flowing backward migration can be divided into two forms of vertical migration and lateral migration. The former occurs when oil-migrating faults develop close to the source reservoir with a certain pressure difference, and the latter occurs as oilmigrating faults develop in a regional caprock sealing area. Through a certain pressure difference between the adjacent source reservoir and oil source fracture overlap, and regional cap covered area and oil source fracture distribution overlap, we established a set of forecasting methods of oil and gas verticaland lateral flowing backward migration patterns in range of distribution, then use them in the forecasting of oil and gas vertical flowing backward migration patterns in range of distribution from oil generated in source of K1qn1 in Sanzhao depression of Songliao basin to Fuyang reservoir, and in the forecasting of gas lateral flowing backward migration patterns in range of distribution from Nanpu depression in Bohai Bay basin along oilmigrating faults to Ed1 reservoir. The result shows that the vertical migration patterns ranges of distribution of oil generated from source of K1qn1 in Sanzhao depression flows backward to Fu Yang reservoirs, distributing in the depression except in local region and edge, and gas transporting to source of K1qn1 in Nanpu depression along oilmigrating faults lateral flowing backward migration patterns in range of distribution mainly spreads in the southwest of the depression, separately consistent with found reservoir distribution of Fuyang reservoir in Sanzhao depression and discovered distribution of gas pools of Ed1 in Nanpu sag at present. It shows that it is feasible to apply two methods separately to predict oil and gas vertical and lateral flowing backward migration patterns in range of distribution.