Study On Petroliferous Conditions Of Gudao Buried-hill In Jiyang Depression, Bohaiwan Basin

Located at Zhanhua sag 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, which stands between the two rich oil source sags of Gubei-Bonan sag and Gunan sag. Therefore, it has the advantageous location and favorable condition for supply and migrationof oil and gas.The low Paleozoic carbonates in the buried-hill have suffered multistage tectogenesis and uplifted, which resulted in extensive karstification and formed karst reservoir. The Guxi, Gunan and Bubei faults, unconformable surface and fracture systems are composed up of the good migration systems for petroleum, and also made the buried-hill be the main area of hydrocarbon migration direction.The source-reservoir-caprock assemblage (SRCA) 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 caprock condition. The most important caprock at the top of the buried-hill is Paleogene 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 straightly contacted with the overlain sandy conglomerate of Guantao formation, which formed escape route way for petroleum. The time of "clerestory window" formation is also the period of Es₃ maturation in Bonan and Gunan sags. It is the escape route way that formed the Gudao Tertiary oil field, the main oil field of Shengli oil field. However, it is also the escape route way that made the main carbonate body of the buried-hill not be large-scale accumulated by the hydrocarbon. Besides, the faults also have the important role at the buried-hill petroleum pool. The movement periods of the faults are also the time of hydrocarbon escape. The vertical unsealing of fault made the lots of hydrocarbon migrate to the overlain Tertiary clastics.Although 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 accumulation. The change of fault sealing can also decide the hydrocarbon migration, accumulation and reservoir formation.