Oil-source Correlations And Hydrocarbon Accumulations Of Carboniferous-Permian In Eastern Fukang Depression,Junggar Basin

The eastern Fukang Depression of Junggar Basin is characterized by diversified hydrocarbon properties and extremely complex oil-source relations,so that large disputes in effective source rocks and hydrocarbon sources have existed for a long term.Oil-source correlations analyses were systematically carried out based on the carbon isotopes and biomarker characteristics.And then the hydrocarbon accumulations patterns of Carboniferous-Permian reservoirs were achieved as well.The results revealed that three types of source rocks were exsisted in Carboniferous-Permian:the dark mudstone on Pingdiquan Formation of Permian,the tuffite and the dark mudstone on Bashan Formation of Carboniferous.The dark mudstone of Pingdiquan Formation was characterized by medium Pr/Ph ratio,medium C₁₉ tricyclic terpane,intermediate C₂₄4 tetracyclic terpane,moderate gammacerane and high regular steranes C₂₇/C₂₉ ratio.The parameters of biomarkers revealed that this type of source rocks was formed on reducible and moderate salinity sedimentary environment and the organic material components were dominated by lower grade aquatic organisms.The tuffite of Bashan Formation was possessed with low Pr/Ph ratio,tiny C₁₉ tricyclic terpane,weak C₂₄4 tetracyclic terpane,but high gammacerane and medium regular steranes C₂₇/C₂₉ ratio.These presentation of biomarkers showed that the Bashan Formation tuffite was produced on reducible and high salinity sedimentary environment and the organic material constituents were similar to that of the Pingdiquan Formation mudstone.The dark mudstone of Bashan Formation was featured by high Pr/Ph ratio,tall C₁₉ tricyclic terpane,lofty C₂₄4 tetracyclic terpane,but tiny gammacerane and weak regular steranes C₂₇/C₂₉ ratio.These data of biomarkers indicated that the Bashan Formation mudstone was developed on oxidized fresh water sedimentary environment and the organic material components included more terrigenous plants input.The first type of crude oil was featured by light carbon isotopes,medium Pr/Ph ratio,tiny C₁₉tricyclic terpane,high regular steranes C₂₇/C₂₉ ratio and low-medium gammacerane.The second type of crude oil was possessed with light carbon isotopes also,tiny Pr/Ph ratio,low C₁₉ tricyclic terpane,intermediate regular steranes C₂₇/C₂₉ ratio and high gammacerane.The third kind of crude oil was characterized by heavy carbon isotopes,high Pr/Ph ratio,high C₁₉ tricyclic terpane,tiny regular steranes C₂₇/C₂₉ ratio and weak gammacerane.The first type of crude oil was distributed on Permian reservoirs in Beisantai oil fields and Shanan oil fields,which derived from the dark mudstone of Pingdiquan Formation.The second type of crude oil was spread on Carboniferous reservoirs and Permian reservoirs of Xiquan oil fields,whose origin was the tuffite source rock of Bashan Formation.The last kind of crude oil was extended in Xiquan oil fields as well,but it only remained on Carboniferous reservoirs in Xiquan 2 Well and Permian reservoirs in Xiquan7 Well.This type of crude oil had a good affinity with the dark mudstone of Bashan Formation.Accordingly,the“exotic source rock-combined pathway system”hydrocarbon accumulations pattern was established according to the distribution of Permian reservoirs in Beisantai oil field.And the“autochthonous source rock-vertical pathway system”hydrocarbon pooling model was constructed based on the extention of Carboniferous reservoirs in Xiquan oil field.