Geochemistry And Genetic Mechanism Of Heavy Oil In The Eastern Chepaizi Uplift,Junggar Basin

In recent years,the exploration and development of Carboniferous volcanic reservoirs in Chepaizi area shows that the Carboniferous reservoirs in eastern Chepaizi uplift has great potential.Carboniferous volcanic reservoirs generally show strong heterogeneity,various occurrences of crude oil and complex distribution of oil and gas.Moreover,Chepaizi uplift has characteristics of multiple oil sources,multiple stages of 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 distributing disciplinarian of oil and gas is not clear,which restricts the exploration and deployment in the next stageThis paper focused on the crude oil of Carboniferous reservoirs in eastern Chepaizi uplift.The source and forming mechanism of the heavy oil of Carboniferous reservoirs in eastern Chepaizi uplift are systematically analyzed through the analysis and testing methods,such as Gas chromatography mass-spectrometry(GC-MS)of the saturated andaromatic fractions,rock-eval,analysis of carbon stable isotopes and fluid inclusionsThe crude oil of Carboniferous reservoirs in eastern Chepaizi uplift is typical heavy oil.And the wax and sulfur content of the crude oil are low.The density of crude oil has certain regularity in horizontal and vertical direction.The crude oil in the eastern and southern of the study area has a higher density and the density decreases with the increase of depth,which due to the migration path of crude oil and secondary adjustment of Carboniferous reservoirsThe crude oil of Carboniferous reservoirs in eastern Chepaizi uplift has relatively low saturated hydrocarbon content,high nonhydrocarbon and asphaltene content and low saturated hydrocarbon/aromatic hydrocarbon ratios;Total ion current(TIC)diagram of saturated hydrocarbons show a clear UCM peak and the loss of n-alkanes and isoprene alkanes is serious,indicating that crude oil has been severely degradedIn order to ensure the accuracy of oil and source rock correlation of crude oil with a complex accumulation background and high degree of biodegradation,a comprehensive oil source correlation method with multiple parameters,multiple indicators and multivariate statistical analysis should be adopted.After the oil source correlation with single parameter,double parameters and multi parameters,the source rocks of the crude oil of Carboniferous reservoirs in eastern Chepaizi uplift is determined as the Permian source rock,which may be mixed with the contribution of Carboniferous source rocks.Biodegradation,oxidation and water washing contribute to the formation of heavy oil in the Carboniferous reservoirs in eastern Chepaizi uplift at different degree.However,the key factor controlling the formation of the heavy oil and the biodegradation level of most of the crude oil is above PM 7+.The influence of oxidation and water washing is covered by severe biodegradation.The crude oil of Carboniferous reservoirs in eastern Chepaizi uplift became heavier under the biodegradation,oxidation and water washing during the process of migration.And after the accumulation,the reservoir adjustment with the tectonic movement results in higher density of crude oil in the Carboniferous reservoirs.