| The Chepaizi Uplift of the Junggar Basin is located in a favorable tectonic position,and the fracture in the area is extremely well developed,which is one of the favorable areas for the migration of oil and gas in the Shawan Depression.Since the first industrial flow of the Well Che 47 in the Carboniferous volcanic rocks was found in 1986,the prelude to the exploration of volcanic rocks has been uncovered.The scale of oil and gas reserves in the study area is considerable and the exploration potential is large.But compared with the conventional oil and gas reservoirs,the development and distribution of Carboniferous volcanic reservoirs in Chepaizi Uplift are complex and diverse,and their reservoir forming rules are complex,and the reservoir forming conditions and main controlling factors have their own characteristics.In order to make a more systematic understanding of the reservoir characteristics of the Carboniferous volcanic oil and gas reservoirs in Chepaizi Uplift,based on the tectonic evolution characteristics and the stratigraphic background of the study area,this paper comprehensively utilized of data of seismic,well logging,mud logging and geochemistry testing data.The typical volcanic reservoirs were dissected,the reservoir conditions were analyzed,the hydrocarbon accumulation rules of volcanic rocks were summarized,the main controlling factors of hydrocarbon accumulation were analyzed,and the reservoir forming models of volcanic rocks were established.The lithology of Carboniferous Reservoir in Chepaizi Uplift mainly includes volcanic breccia,tuff,andesite and basalt.The reservoir space mainly consists of secondary pores and fractures and other secondary reservoir spaces.The physical properties of eruption facies and volcanic sedimentary facies are favorable,while the physical properties of overflow facies are poor.They are mainly medium porosity and low permeability reservoirs,and the reservoir heterogeneity is strong.The correlation of porosity and permeability,as well as the relationship between physical property and depth,are poor,and the physical property of reservoir is closely related to the distance from the Carboniferous top unconformity.The development of the reservoir is influenced by tectonic movement,lithologic facies of volcanic rocks,and the effect of weathering and leaching.The Chepaizi Uplift mainly developed three sets of potential hydrocarbon source rocks,the lacustrine mudstone in the Permian Fengcheng,Wuerhe and Jiamuhe formations,respectively.The Jiamuhe Formation source rocks have low organic matter content,found only in a few areas,while the hydrocarbon generation potential of Permian Fengcheng and Wuerhe formation are huge.According to oil-source correlation,the Chepaizi Carboniferous crude oils have high maturity,and the distribution types of C20,C21 and C23 triterpanes are mainly C20<C21<C23 type and C20<C21>C23 type,which shows that oil and gas mainly from Fengcheng Formation and Wuerhe Formation.There are at least two periods of accumulation and one period of adjustment for the formation of current oil and gas reservoirs.According to the analysis of typical oil and gas reservoirs,the density,viscosity and group compositions of the crude oils in the study area are different,but there is little variation of the wax content and freezing point.The composition of crude oil is characterized by high content of saturated and aromatic hydrocarbon,and low content of non-hydrocarbon and asphaltene.The density of the oil and gas from the Permian Fengcheng Formation and Wuerhe Formation is different.The hydrocarbon accumulation of volcanic rocks is mainly controlled by the development of fractures,lithofacies distribution and unconformity surface.In plane,it is mainly controlled by faults and volcanic facies.Vertically it is mainly controlled by paleo-uplift and volcanic eruption.The Carboniferous reservoirs are mainly distributed within the range of 400m from the top boundary of Carboniferous. |
