Formation Mechanism And Displacement Efficiency Of Film-Like Remaining Oil In Water Drive Reservoirs

Micro oil displacement is mainly to study the mechanism of displacement fluid and displaced fluid in the pores and the distribution of remaining oil.Due to the complexity of rock pores,remaining oil is distributed in the pores in the form of oil drops,oil films and so on.In the process of water flooding and oil recovery,the remaining oil of oil film type accounts for a large proportion,and its formation is related to many factors,including the different components of crude oil,the size of porosity,the distribution of pores,etc.Based on the theory and method of reservoir physics,fluid mechanics and percolation mechanics,this paper studies the formation mechanism and displacement efficiency of oil film type remaining oil in water drive reservoir.The research results of this paper are as follows:(1)The causes of the imbalance of suspension,dissolution,deposition and dissolution of heavy organic matter in crude oil are analyzed.The main influencing factors are the complexity of crude oil components,the reaction between crude oil and rock particles,the colloidal effect,the electrokinetic effect and the polarity of glial asphaltene.(2)In this paper,the stress of the remaining oil in the pore channel is studied.The forces of remaining oil include gravity,buoyancy,interfacial tension of oil film surface,capillary force in capillary,friction between pipe wall and oil,and viscous force due to the viscosity of oil.(3)The influence of water displacement velocity in capillary pores on oil film thickness and oil displacement efficiency is analyzed.When the pressure gradient is increased,the displacement velocity will increase,resulting in the relative velocity difference between the displacement phase and the displaced phase.It is affected by the force and drives the oil phase movement.(4)The concept physical model of capillary oil displacement is established,and the empirical equation of remaining oil film thickness is derived.With a certain capillary radius,the thickness of the boundary layer becomes thicker with the increase of crude oil viscosity.The greater the content of heavy components in crude oil,the more adsorption deposition of polar components,the greater the crude oil viscosity.The thicker the boundary layer is,the more obvious the non-Darcy seepage characteristics are.(5)The relationship between viscosity change of oil film and shear force in pores and the influence of roughness on remaining oil are analyzed.And the oil displacement effect formula considering roughness is established.In the process of the oil film being driven,the remaining oil film will deform,which occurs layer by layer;with the displacement,the closer the oil film is to the wall of the channel,the greater the viscosity,the greater the viscous shear force.After the oil film deforms,it will reach equilibrium again.In the real pores,the correction factors such as curvature,shape factor and roughness should be added,and the heterogeneous layer should be equivalent to equal diameter / unequal diameter bundle to study the displacement efficiency.