Research On Geochemical Characteristics And Accumulation Process Of Upper Paleozoic Reservoir In Hashan Area

Hashan Area is part of the foreland belt,which is adjacent to the source rock sag.Due to the complex tectonic structure background,the source rocks become extremely anisotropic,the maturity is quite different and the petrology of reservoir is volcanic rock with variety of lithofacies.There are multiple types of oil and gas in part of the study area.Although oil and gas shows in many wells,the hydrocarbon distribution characteristics and the accumulation mechanism remains unresolved.This research will enhance the understanding of mechanism of oil accumulation and provides useful reference for petroleum exploration.In this paper,based on the distribution characteristics of oil and gas,we carefully analysised the geochemical characteristics of all kinds of oil and gas.The oil genetic types have been classified and compared,the formation mechanism of different kinds of crude oil have been discussed.We solved the main problem such as reconstruction of burial history,the palaeogeothermal was used to analyze the relationship between the different types of oil and gas accumulation and tectonic movement.The fluid inclusion analysis was used to rebuild the process of oil and gas accumulation in differently tectonic units.The results point out the key control factors of geological buried history,establishing the dynamic accumulation patterns.As the results,the oil was divided into three categories based on the maturity of crude oil: immature oil(A),mature oil(B,D)and mixed oil(C).The immature oil can be further seperated into two classes(A1,A2)according to the oil biodegradation degree.The mature oil can be divided into six categories(B11,B12,B21,B22,B3,D)according to the maturity,ratio of pristine to phytane and oil biodegradation degree.Immature oil(class A)is mainly distributed in the tectonic triangle zone B,frontal thrust belt,nappe II,III.Mature oil(B,D)is mainly distributed in nappe II,III,IV and tectonic triangle zone A.Mixed source oil(class C)is distributed in the central of study area.Differently matural oil all come from the Fengceng Formation,the low maturity oil(A)in the west of Hashan is mainly from the source rock of the Fengceng Formation with relatively low maturity.The mature oil(B1,B3 and D)in the west of Hashan is from the source rock in the slope belt of the deep Hashan and Mahu sag with the high maturity.The crude oil(B2)in Hashan is from the source rock of the sedimentary center of Fengcheng Formation nearby the Fenggu 4 well zone.In the study area,hydrocarbon accumulation generations have some differences.Immature oil in west of Hashan filled in Permian.In tectonic triangle zone A the oil filled at the early and late Permian.In nappe II,III the Oil filled at Permian and Triassic.In Hashan 2 well the oil reservoirs was filled at late Permian and Jurassic.Generally,there are three hydrocarbon accumulation generations,relatively occurring in Permian,Triassic and Jurassic.Hydrocarbon accumulation model in study area is involved coupled source rock and multiple reservoir,controled by the faults.The oil and gas accumulation were coevally controlled by the source rock distribution,mature time,tectonic evolution stage and reservoir lithology.Finally,the hydrocarbon accumulation formed complex phases of oil and gas,distributed in the study area.