Hydrocarbon Migration Transportation System In Nanpu Sag's Middle-shallow Layer

Based on the geochemical characteristics,hydrocarbon migration,sand body and fault transport system of No.2 structure's oil and source rocks in Nanpu Sag,this paper divides the types of oil source faults and clarifies the sand bodies and faults'effection in oil and gas transmission and solved the problem of middle-shallow layer's hydrocarbon migration and its differential enrichment in the study area.According to the different geochemical characteristics of crude oil,it can be divided into two types:Among them,type A crude oil is widely distributed in the study area,mainly concentrated near the NP2-1 well.Type B crude oil is less distributed and only concentrated in local areas near the NP23-X2407 well.According to the differences in geochemical characteristics of source rocks,source rocks can be divided into two types:Es source rocks?Type ? source rocks?and Ed₃ source rocks?Type II source rocks?.According to the oil source comparison analysis,the type A crude oil is derived from the type ? source rock;the type B crude oil and the type I source rock are more similar in geochemistry.According to the structural form of the fault and the cut-off layer's characteristics,the oil source fault of No.2 structure belt in Nanpu Sag can be divided into three types:oil source fracture of Es₂₊₃,Es₁and Ed₃,and the main active period of the fault is concentrated in the end of Nm,Es and Ed.In addition,according to the spatial distribution characteristics of crude oil and oil source fault,combined with the oil source comparison analysis,it is concluded that the active oil source fracture is the main channel for the oil and gas distributed in deep strata to migrate to the middle and shallow strata in the study area.Through the study of crude oil's physical properties,biomarker and formation water's characteristics in the study area,the middle and shallow oil and gas in the No.2 structure belt of the Nanpu Sag migrated from northeast to southwest along the tectonic ridge in the plane,and finally gathered in high position.In the vetical section,the oil and gas migrated along the active oil source fracture from the deep hydrocarbon source rock layer to the shallow reservoir.In general,the direction of hydrocarbon migration in the study area is lateral migration along the oil source fracture to the high position.The study on the distribution of oil and gas in the middle and shallow layers of the No.2 structure belt in Nanpu Sag and the study of oil and gas transmission system summed up two modes of hydrocarbon migration and enrichment transportation in the middle and shallow layers:source-fault transport system and source-fault-sand transport system.The No.2 structure belt in Nanpu sag's transport system is dominated by the source-fault-sand combination which controls the formation and distribution of oil and gas in the study area.