Different Hydrocarbon Accumulation In The Carboniferous Volcanic Reservoirs Between The Eastern And Western Chepaizi Uplift,Junggar Basin

In recent years,the exploration and development of Carboniferous volcanic reservoirs in Chepaizi Uplift shows that the Carboniferous reservoirs in Chepaizi Uplift has great exploration potential.The Carboniferous volcanic reservoirs of Chepaizi Uplift has characteristics of multiple oil sources,multiple stages of hydrocarbon accumulation,and large variation of crude oil density.It is unclear that the process of oil filling and adjusting from different sources due to the tectonic movement.The hydrocarbon accumulation disciplinarian in the region are unclear,which restricts the exploration and deployment of the next step.In this paper,the oil source complexity and accumulation complexity of the Carboniferous crude oil in Chepaizi Uplift were studied.The oil source of the Carboniferous crude oil and its reservoir-forming differences are systematically analyzed through the analysis of Gas Chromatography Mass-Spectrometry(GC-MS)of the saturated and aromatic fractions,MS/MS analyses of saturated fractions,rock-eval,the stable isotope of whole oil,bulk composition and monomer hydrocarbons,inorganic element analysis,comprehensive analysis of fluid inclusions,etc.The Carboniferous crude oil in the eastern Chepaizi Uplift is a typical heavy and highly viscous oil,and the viscosity has a large range of variation with increasing density.The Carboniferous crude oil in the western Chepaizi Uplift is mostly light-medium to medium,medium-viscous to high-viscous oil,and the viscosity increases little with the increase of density.In addition,the density of crude oil also shows a certain regularity in the horizontal directions.The crude oil in the eastern and southern of the study area has a higher density,which due to the difference of biodegradation of crude oil and the difference of hydrocarbon accumulation.Therefore,based on the analysis of the difference of physical and geochemical characteristics of crude oil,based on the characteristics of extremely biodegradation in Chepaizi Uplift,rational selection of geochemical parameters using hierarchical clustering analysis to classify Carboniferous crude oil in Chepaizi Uplift into two oil populations,four family.The degradation degree of crude oil in each family was analyzed by combining PM method and Manco method,it was found that the degradation degree of crude oil gradually increased from family I to family ?2.In view of the characteristics of multi-source and multi-stage accumulation and extremely biodegradation,the selected correlated parameters should reflect the organic source characteristics and thermal maturity level,and remain basically unchanged in migration and secondary degradation.Due to the extremely biodegradation of the crude oil in the eastern Chepaizi Uplift,the relatively well-degraded oil family(?)were selected to the oil-source rock correlation.In order to prove the difference between the source environments of several sets of potential source rocks,the sedimentary environment of source rocks were analyzed by combination of trace element analysis(inorganic)and molecular analysis of compounds(organic).In addition,in order to ensure the accuracy of the oil-source correlation,firstly select the geochemical parameters that are not affected by biodegradation and secondary alteration as much as possible,and then,the principal component analysis method is used to reduce the dimension,and the oil source of each crude oil population is visually analyzed by a three-dimensional map.Through spectral comparison,comparison of two-parameter and multi-parameter oil sources,it is concluded that the oil source of the Carboniferous crude oil in the East Wing of Chepaizi is mainly composed of Permian source rocks,which may be mixed with the contribution of Carboniferous source rocks.However,the oil source of the Carboniferous Crude Oil in the western Chepaizi Uplift may be mainly the input of the Jurassic source rocks in the Sikeshu Sag.Then,based on the grey relational theory,the contribution rate of the oil source is analyzed.It can be seen that the contribution of the Permian source rock in the mixed oil of the eastern Chepaizi Uplift can exceed 90%,and only exists a small contribution of Carboniferous source rocks.Finally,through the comprehensive analysis of fluid inclusions(petrographic characteristics,single polarization-fluorescence characteristics,microthermometry,density and pressure characteristics,etc.),it is confirmed that there exists two periods paleo-fluid filling process in eastern and western Chepaizi Uplift.The paleo-fluid filling time of the two periods were determined by combining the history of source rock maturity,the development history of traps and the history of diagenesis.The results show that the hydrocarbon source rocks of the western Chepaizi Uplift are relatively late compared with the eastern Chepaizi Uplift due to the relatively new source rocks and the new overburden rocks.It is speculated that the first period of the eastern Chepaizi Uplift was formed at the late Cretaceous to Paleogene,and the second period was the adjustment charging process since the Neogene.The two periods of paleo-fluids in the western Chepaizi Uplift may be continuously charged,so it can be inferred that the Carboniferous reservoir of western Chepaizi Uplift is filled with Neogene and Quaternary.From the perspective of differential hydrocarbon accumulation,the distribution of homogenization temperature of fluid inclusions in the western Chepaizi Uplift(100-200?)is higher than that in the eastern Chepaizi Uplift(60-160?),which may be related to the geothermal field of Jurassic period in the western Junggar basin(2.25?/100m)is higher than the Permian period(2.09?/100m).In addition,compared with the western Chepaizi Uplift,the density of the second period of paleo-fluid of the eastern Chepaizi Uplift(1.025g/cm3<p<1.10g/cm3)is significantly higher than the first period(0.925g/cm3<p<1.025g/cm3).The density of the two phases of the West Wing is approximately 0.90g/cm3<?<1.00g/cm3,indicating that the second period hydrocarbon-bearing fluid in the eastern Chepaizi Uplift may suffered serious secondary changes.By summarizing the characteristics of Carboniferous reservoirs and controlling factors of hydrocarbon accumulation,the hydrocarbon accumulation model of Carboniferous in Chepaizi Uplift was established.The Carboniferous accumulation model of Chepaizi Uplift can be summarized as follows:two hydrocarbon kitchen supply,fault-sheet sandbodies transport,and edge of sheet sandbodies-weathering crust of top of Carboniferous strata.