Research Of Hydrocarbon Reservoir Accumulation Feature Of Carboniferous In Chepaizi Area,Junggar Basin

Chepaizi area is located in Chepaizi bulge of Junggar basin.It is adjacent to Changji depression in the east through the Hongche fault.The exploration coverage is 1020km2.Chepaizi area is a hydrocarbon accumulation area with multi-layer and multi-type,and at present the major exploration strata are N1 s and C2.Recently Pai61 and Pai66 wells get commercial oil flow from Carboniferous,which indicated that Carboniferous will be an important exploring stratum in Chepaizi area.However,Carboniferous of Chepaizi area is in low research level,there are three critical problems need to be resolved:(1)the distribution and lithological sequence of Carboniferous is not clear;(2)the category and distribution of available reservoir strata is not clear;(3)the hydrocarbon reservoir accumulation feature and favorable exploratory area is not clear.These problems have limited the exploration process of Carboniferous in this area.This thesis attempts to solve them and get some achievements.Carboniferous of Chepaizi area can be divided into C1 t,C1+2b and C2 x.At present the drilling stratum is C2 x in all.The Lower Carboniferous is widely distributed in Junggar basin.The Upper Carboniferous is severely denuded,but it is still arresting distributed in Chepaizi area.By means of “logging recognition technology of complex volcanic rocks”,Carboniferous volcanic rocks were successfully identified.Then we find out that Carboniferous have various kind of volcanic and sedimentary rocks.The volcanic rocks mostly distribute in C1 t and C2 x,and the sedimentary rocks mostly distribute in C1+2b.Carboniferous reservoir spaces are mainly secondary dissolution pores and fractures.The fractures provide main flow channel.Cracks,lithologic facies and dissolution jointly control reservoir development.On the plane,reservoir development band is mainly along the major fault,which play a leading role in reservoir formation.On facies,volcanic breccia and tuff of outbreak phase combined with andesite of overflow phase are more easily form good secondary porosity and cracks.On cross-section,the reservoir distributed mainly in 500 m from the weathering crust.Oil which generated from Permian and Jurassic source rocks in Changji depression could flow along the fault and regional sandstone,then gathered in favorable structural or stratigraphic traps which had good dissolution pores and fractures.This is typical combination of new source-ancient reservoir.The controlling factors of accumulation are as follows:(1)regional sandstone of good physical property provided favorable migration condition;(2)good lithologic facies provided favorable occurrence condition;(3)the fine shell in the face of Carboniferous was the critical condition to the extensive accumulation.The accumulation mode is as follows: Oil generated from Permian,migrated along the faults and regional sandstone,good lithologic facies controlled the accumulation,and the fine shell sealed hydrocarbon.The reservoir type is fault block hydrocarbon reservoir.