Characteristics And Main Controlling Factors Of Cretaceous Reservoir In East Flank Of Chepaizi Area

This paper takes the Cretaceous reservoirs in the eastern region of Chepaizi area as the object of study,and applies the hydrocarbon accumulation geology.With the data from drilling,logging,and geochemical experimental analysis,reservoirs types,reservoir-cover assemblage,migration pathway system,fluid properties,temperature and pressure characteristics were analyzed,and the main controlling factors and accumulation model were summarized.It was concluded that the Cretaceous of the eastern region of Chepaizi area is mainly stratigraphic-lithologic and fault-lithologic complex reservoirs.The oil and gas are mainly accumulated above the unconformity at the bottom of the Cretaceous.Longitudinally,the closer to thinning out of strata the thicker the oil layer is.Horizontally,the reservoirs area developed near the thinning out of strata is large,while the size and shape of the reservoirs at the faults are different.The complex migration pathway system composed of unconformities,faults and sands is the main controlling factor for the formation of Cretaceous oil and gas in the eastern region of Chepaizi area.The unconformity determines the communication with the oil source,and the HMIe is generally greater than 0.7.The effective transmission thickness corresponds to the three types of migration channels,and oil and gas can be migrated with the unconformity surface.The size of the faults controls the reservoirs size and there are differences in the confinement of the faults,which affects the oil and gas filling.The Rm is 0.45-0.8,and the K is generally greater than 2.5.The Cretaceous beach bar sand body and fan delta sand body have poor connectivity and control the lateral adjustment of oil and gas migration,while the Jurassic top blanket sand generally has oil and gas and connects with the Changji depression and connects with the unconformity at the bottom of the Cretaceous.It is concluded that the Cretaceous reservoirs in the eastern region of Chepaizi area have reservoirs forming characteristics such as lateral hydrocarbon supply,long-distance migration of oil and gas,two-stage fillings,complex migration,biodegradation and multiviscosity,and multi-step reservoirs formation.