Pressure Evolution and Hydrocarbon Migration-Accumulation in the Moliqing Fault Depression,Yitong Basin,Northeast China

The Yitong（伊通） basin is a Late Mesozoic and Cenozoic continental sedimentary basin in Northeast China.On the basis of well tests and seismic data,we use the 2D modeling technique to rebuild the pressure evolution and hydrocarbon migration in the Moliqing（莫里青） fault depression of the Yitong basin.Based on the modeling results,four conclusions are drawn as follows.（1） The Eocene Shuangyang（双阳） Formation within the Moliqing fault depression had entirely undergone three epi-sodic cycles of pressure accumulation and release in geological history,and the three tectonic move-ments since the Middle Eocene played important roles in the episodic changes of excess pressure.（2） The present formation pressure distribution is characterized by normal pressure in almost the entire fault depression with some residual overpressure.The differential distribution of pressure results mainly from the difference in rock facies,sedimentation rate,hydrocarbon generation,and fault activi-ties.（3） The hydrocarbon migration is more active during the release of pressure in the Moliqing fault depression,which happened mainly in the Middle-Late Oligocene and provided the driving force for hydrocarbon migration.（4） The hydrocarbon migration was mostly directed to the Shuangyang For-mation within the Jianshan（尖山） uplift and the Kaoshan（靠山） sag.With the superior condition ofhydrocarbon accumulation and the higher de-gree of hydrocarbon concentration,the north-west part of Kaoshan sag is considered a favor-able area for oil and gas exploration in the Moliqing fault depression.