Study On Petroliferous Characteristic Of Gudao Buried-hill In Zhanhua Depression

Located at Zhanhua depression in the northeast of Jiyang Depression, Bohaiwan basin, Gudao buried-hill is a fault-block buried-hill. The buried-hill is inclined to northeast and controlled by Guxi, Gunan and Gubei faults, it stands between the two oil source sags of Gubei-Bonan sag and Gunan sag, has the advantageous location and favorable condition for supply and migration of oil and gas.The low Paleozoic carbonates in the buried-hill have suffered multistage tectogenesis and uplifted, which resulted in extensive karstification and formed karstic reservoir. The Guxi, Gunan and Bubei faults, unconformable surface and fracture systems are composed of the good migration systems for petroleum and gas, and made the buried-hill be the main area of hydrocarbon and migration direction. The source-reservoir-caprock assemblage of Gudao buried-hill is low source-up reservoir-top caprock. The hydrocarbon pool belongs to "new source to old reservoir".The important factor to control the hydrocarbon accumulation and pool is the condition of caprock. The most important caprock at the top of the buried-hill is Paleocene Dongying formation. However, the Dongying formation at the top of the buried-hill was denuded by the tectonic uplift during the late of Dongying formation. It formed a "clerestory window'' with 1.84 km2. The main body of the buried-hill directly contacted with the overlain sandy block of Guantao formation, which formed escape route for petroleum and gas. The time of "clerestory window" formation is also the period of Es3 maturation in Bonan and Gunan sags. It is the escape route that made the main body of the buried-hill not be large-scale accumulated by the hydrocarbon. The faults play a important part at the petroleum accumulations of The buried-hill. The movement periods of the faults are also the time of hydrocarbon escape. The vertical unsealing of fault made the lots of hydrocarbon migration to the overlain Tertiary era.Therefore, the Gudao carbonate buried-hill is uplifted and located between rich petroleum source sags, it was the main area for hydrocarbon migration but not the most advantageous hydrocarbon accumulation zone. The caprock condition is the most important factor of the buried-hill petroleum and gas accumulation. The change of fault sealing can also decide the hydrocarbon migration, accumulation and reservoir formation.