The Study On Policy Optimization Of Huff And Puff Type Of Secondary Gas Cap Drive Technique

In recent years,most of the mid-high permeability conventional maturing fields in China have gradually entered the extra-high water cut development period,making hydrocarbon production faced with tremendous pressure and challenges.Complex fault block reservoirs,as one of the important hydrocarbon sources in China,are characterized by complex structure,small oil-bearing area and high stratigraphic dip.It is hard to form a complete well pattern system,which means tapping the potential of "attic oil" retained at the top of the structure becomes more difficult.As a method to effectively maintain producing energy and improve displacement efficiency,huff and puff type of secondary gas cap drive has been proposed and applied to the development of complex fault block reservoirs.With the constant development of exploration technology and injection-production technology,how to further optimize this technique to produce "attic oil" more economically and efficiently is of great significance for the development of complex fault block reservoirs in China and even the world.Aiming at the typical characteristics of complex fault block reservoirs,combined with filtration theory and reservoir engineering methods,this paper researches the seepage law of nitrogen flooding under huff and puff mode,and determines the formation condition of secondary gas cap drive by referring to the classification criteria of gas cap index.Meanwhile,this paper discusses the synergistic mechanism of enhancing the "attic oil" recovery of the complex fault block reservoirs by huff and puff type of secondary gas cap drive,taking into account the dynamic variation rule of fluid flow direction,secondary gas cap and oil-gas interface during huff and puff process.Based on the above theoretical basis,with reservoir numerical simulation method,this paper studies the factors influencing the displacement characteristics of secondary gas cap from three aspects as reservoir structural conditions,reservoir physical properties and crude oil properties,to establish the block screening conditions of complex fault block reservoirs suitable for single well nitrogen huff and puff development.On this basis,the policy limitation of injection and production dimensionless parameters of secondary gas cap drive is formed.The rationality of this policy limitation is verified by the application evaluation of the actual working area.The implementation of this technique to tap the potential of "attic oil" provides technical support and guiding significance for complex fault block reservoirs.