The Study On The Fault Structure And Its Sealing Ability Of Chepaizi Uplift

This article detailed the fault Characteristics and its accumulation-controlling mechanism in the West Wing of Chepaizi Uplift to guide petroleum exploration.Based on the analysis of seismic and well logging data,faults in the west wing of Chepaizi Uplift were created in three stages and can be devided into upper and lower parts bounded by the unconformity on the top of cretaceous,the upper part consists of normal faults and the lower part consists of thrust faults.Lower faults controlled the formation of upper faults and the deposition of Jurassic in which sand formations and faults are the main migration pathways.According to tectonic evolution study,faults were activitive from Triassic to early Jurassic,and hydrocarbon started to generate in cretaceous,faults play an important role in oil and gas migration and accumulation.Based on the devision of the fault belt structure,the scale of faults is related to the fault belt structure,and when fault is buried deeper,its structure will be more apparent.Based on the analysis of seismic and well logging data,relation of cross-fault lithology juxtaposition and some other factors,Faults have high sealing ability in Shaer formation while have low sealing ability in Shayi and Jurassic formation in which mainly act as migration pathways in Chepaizi Uplift and Aika fault belt have good sealing ability at present,and the sealing ability decreases from the middle to both ends.While during accumulation period,faults have low sealing ability and increases from the middle to both ends.The sealing ability of Badaowan formation is lower than Sangonghe formation,the hanging wall's sealing ability is higher than footwall which resulted into the oil accumulation at hanging wall,and according to the analysis of the fault sealing ability.During reservoir-forming stage,the pressure on the fault surface is relatively low,rock deformation effects are not strong enough to close the fault belt and also resulted into the low shale smear and filling effects,so fault sealing ability during reservoir-forming stage is lower than present as a whole.And because of the similar lithology,shale smear and filling effects are of little difference between hanging wall and footwall,which result into the similar fault sealing ability.Based on the analysis of faults' accumulation controlling mechanism,faults play different roles in different area,and controlled the trap effectiveness,and also act as migration pathways,connected the lower and upper oil,even controlled the distribution of reservoirs.Taking all factors into consideration,Three migration pathways and three types of accumulation model resulted into the formation of the dominate stratigraphic and lithologic reservoir,which has the character of “migrating low,accumulating high”.