Abstract: The genesis of oil-associated CO₂ and its impaction on the exploration of oil reservoir and the dynamic accumulation for oil and gas have been investigated by studying on the oil-associated gas and the dawsonite-bearing sandstones in Changling depression, southern part of Songliao basin. The characterists for oil-associated CO₂ in southern part of Songliao basin are showing a content of CO₂ between 1.57% and 75.25%(most of which are higher than 20%), with δ¹³C_CO2  values from -9.90‰ to -4.00‰, and R/R_a values in the range of 0.95-4.46. It is suggested that the content of CO₂ in oil-associated gas is high, and most of the CO₂ is mantle-magmatic origin. When there is a large-scale mixed CO₂, a secondary oil reservoir will form owing to the displacement of crude oil by CO₂. The scenario of oil displacement by mantle-magmatic CO₂ has been recored by the typical profiles of oil and gas reaervoir in south of Songliao basin and the primary hydrocarbon inclusions in dawsonite cements. Therefore a new exploration idea is made to looking for the secondary oil reservoirs origined from oil displacement by CO₂ within the place mixing with mantle-magmatic CO₂ and oil reservoir.

Key words: oilasscciated CO2 gas, oil displacement, secondary oil reservoirs, dawsonite, south of Songliao basin, petroleum gas