Abstract:

Songliao Basin is a superposed basin composed of fault-subsidence and depression. The pool forming system of the fault-subsidence was controlled by faulting and subsiding intensity. The source rocks of the basin are mainly type-Ⅲ and type-Ⅱ_B of high thermal evolution. Hydrocarbon generation took place quite early and most of the hydrocarbon is natural gas. Hydrocarbon migrated vertically through faults and fractures associating with lateral migration along T₃, T₄ interfaces. Traps such as contemporaneous, early stage structural and multistage composite traps are favourable for trapping oil and gas. Since the traps are small,source rock are dispersive and posttectonic reworking was intensive, the pool-forming efficiency is quite low. As for the depressed basin, its source rock distribution is stable and extensive, the kerogens are primarily type-Ⅰand type-Ⅱ_A,and on the whole,the evolution degree of organic matter is lower. Hydrocarbon, mainly oil associated with gas, generated late in the depressed basin. Oil and gas in the basin migrated laterally along T₁, T₂ interfaces and reservoirs. Verious kinds of traps superposed on paleo-uplifts and paleo-slopes are more favourable to form oil and gas pools.