Caoqiao-Guangrao Buried hill is situated in the south section of the south slope of Dongying Depression and developed in late Indosinian stage.The buried hill is in structural culmination

faults and unconformities developed well in the buried hill

so it has favourable migration pathways.Ordovician sediments are the main reservoir rocks

fractures

solution cavities and pores are the major preserving spaces;Sha 4 submember-Kongdian Formation mudston is regional cap rock.Solution

buried hill structural pattern and cap rock distribution were the controlling factors of oil pool forming.Now top and inside oil pools have been discovered in the buried hill.