Volcanic Activities and Hydrocarbon-generating History in the Changling Fault Depression,Songliao Basin

The seismic stratigraphy of the well SN109 shows that the Changling fault depression has three relatively large volcanic activities during rift faulting.Under the three hot events,organic matters were in higher thermal evolution environment during the early stage of deposition,which speeded up maturation of source rocks.Shahezi and Yingcheng Fm.began to generate hydrocarbon in about 122Ma(late Denglou Fm.) at a burial depth of 1500m,and the Ro value reached 0.5%,but at that time,there were no effective caprocks.When the Ro value reached 1.3% in 119Ma(late Quantou Fm.) at a burial depth of 2600m,source rocks entered the peak of gas generation and pyrolysis gas stage.At the same time,the caprock of Quan-2 Member had just deposited,natural gas were primarily dispersion.When the Ro value reached 1.3%～2% at 95Ma(late Qingshankou Fm.),the caprock of Quan-2 and Qing-1,Qing-2 Member deposited,and a large quantity of pyrolysis gas and high maturity natural gas accumulated.Now the natural gases in the reservoir are mainly dry gas.The exploratory direction in this area should strengthen the study of paleostructure and gas reservoir at the basin depression and slope.