Research on Migration and Accumulation Mechanism of Hydrocarbon “Reversed Migration” in Fuyu and Yangdachengzi Formation  in Sanzhao Depression

Key words: 
• Sanzhao depression /
• Fuyang Formation /
• reversed migration /
• oil source fault /
• fault concentration belt /
• footwall fluvial channel sand /

Abstract: There is abundant oil and gas in F,Y Formation of Sanzhao depression in Songliao Basin, how to further enlarge reservoir area and how to exploit proven territory are two problem puzzling explorer because of the complexity of reversed migration. The distinctiveness of accumulation of F,Y Formation are manifested in two aspects: first, higher density fault, smaller scale and concentrated in zone; second, it's difficult to forecast distribution of the fluvial channel sand since F,Y Formation located in convergence of provenance. This paper based on the correlation of oil and gas, centering on the formation and evolution of fault, oil source fault is calibrated, the allocation of fault and sand body and regulation of controlling oil has been analyzed and the accumulation model is established. It's considered that the oil of F, Y Formation mainly comes from the hydrocarbon source rock of K1qn, the key period of accumulation is last sediment stage of K2m, consequently, the main oil source faults are those among the periods of fault depression to depression and depression to inversion, reversed migration happened along the oil source fault under the action of overpressure, the depth downward is usually 200m, so the favorable formation of interest is the top of F,Y Formation. Faults in F,Y Formation is featured by concentration in zone, oil source faults , the ones controlling accumulation, are mainly the boundary faults. The force condition of "reversed migration", namely, oil along oil source faults, multiple phases of deformation of faults and transportation of horizontal fracture caused by the decoupling of mudstone of K1qn in reversed period determined the concentration of oil in footwall channel sand of fault, oil in horst controlled by oil source fault is highly concentrated, whereas the concentration zone of fault which is the lower tectonic place is not concentration area of oil.