Petroleum Origin And Accumulation Pattern Dominated By Source-Fault-Reservior In The Nanpu Sag, Bohai Bay Basin

Geochemical characteristics of the oil and gas in the different belts in the Nanpu Sag are varied,of which the research on the genetic mechanism is weak.To investigate the petroleum origin,accumulation and distribution in the Nanpu Sag,the static and dynamic characteristics of the reservoirs and the main controlling factors of petroleum accumulation are studied by oil/gas-source correlation,basin modeling and fluid inclusion analysis in this paper,based on the experiments of the source rock and oil samples.This paper shows that biomarker association,including C₂₇ diasteranes,gammacerane and 4-methyl steranes,of different souce rocks in the Nanpu Sag are varied.The petroleum origins of the reservoirs on the both sides of the Gaoliu fault are different,which is the result of the lateral seal of the Gaoliu fault and the occurrence of the varied source rocks on the both sides of the fault.The petroleum origin of the reservoirs overlying the source rock layers in the different structural belts on the south side of the Gaoliu fault are different,which is the result of the varied relations of spatial disposition of the source rock,reservoir and fault.The source rock of the third member of the Shahejie formation?Es₃?makes significant contributions to the reservoirs in the Nanpu 5,1 and 2 structural belts,which is the result of the occurrence of the fan delta or braided river delta sand in the Es₃.Comparatively,the Es₃ source rock makes little contribution to the reservoirs in the Nanpu 4 and Gaoliu structural belts,which is the result that the fan delta or braided river delta sand is not developed in the Es₃.It has been proved that the reservoirs overlying the source rock layers are secondary by varied maturity of the shallow and deep oil,and varied gammacerane content of the oil from the reservoirs overlying the source rock layers.Petroleum origin and accumulation pattern dominated by source-fault-reservior has been built in the Nanpu Sag in this paper,which is presented that the oil/gas origin,accumulation time,distribution,type,and oil saturation of the reservoirs,and the reservoir improvement are controlled by the source rock,reservoir and fault.The pattern dominated by source-fault-reservior in the Nanpu Sag are divided into two sub-patterns:the pattern on the north side of the Gaoliu fault?Pattern1?,characterized by one source rock,weakly active faults and the main oil/gas distribution in the reservoirs in the source rock layers,and the pattern on the south side of the Gaoliu fault?Pattern 2?,characterized by multiple source rocks,many strongly active faults and the main oil/gas distribution in the reservoirs above the source rock layers.The pattern dominated by source-fault-reservior is universally applicable in the Bohai Bay Basin,which has guiding significance to the petroleum prospective.The petroleum origin and accumulation in Bozhong,Zhanhua and Qikou sags,etc.,belong to the Pattern 1,the petroleum prospective should focus on the reservoirs above the source rock layers.Comparatively,the petroleum origin and accumulation in Dongying,Liaohe West,Weibei and Langgu sags,etc.,belong to the Pattern 2,the petroleum prospective should focus on the reservoirs in the source rock layers.