Abstract:

The Lujiabao Depression,situated in the east part of the inner Mongolia withan area of 2500 km²,is one of the two biggest depressions in the Kailu Basin.The basement consists of hypergone metamorphic rocks of the Carboniferous-Permian Systems and the sediments with the total thickness of 5000m inthe basin are mainly made of Upper Jurassic,Cretaceous and few Cenozoic.Its evolution can be divided into two.stages.Fault-subsidence occurred in theLate Jurassic and depression in the Early Cretaceous.The Fuxin,Shahai andJiufotang Formations of the Upper Jurassic are considered as three source beds.The former is a poor one belongs to sapropel type,the latter two are betteror fine ones with abundant organic matter,of which the first two are sapro-pelic and the last belongs to humosapropelic type.In accordance with the ratioof hydrocarbon transformation,and of vitrinite-reflectance and OEP value,oil-generating threshold is determined to be 1400m in depth,lower-maturationstage is in 1400-1780m,and maturation stage in 1780-2200m.It is suggestedthat the Jiufotang and Shahai Formations have reached the oil threshold,andthe valuable thickness of source rocks is about 700m.Sandstones and contem-poraneous faults and secondary structures related to faults are well develo-ped in the depression.The formation time of traps coordinated with that ofoil-gas generation,thus oil show has been discovered in 5 wells there.