Optimization Research Of Binary Combination Flooding In W5 Mid-low Permeability Common Heavy Oil Reservoir

In order to solve the problem of low recovery rate of water flooding in Mid-low permeability common heavy oil reservoirs,the applicability of chemical flooding in Mid-low permeability heavy oil reservoirs was studied in W5 block of jiangsu oilfield(permeability lower than 200×10^-3μm²,crude viscosity is 218.94-292.3 m Pa·s).Firstly,the viscosity characteristics of polymer and amphoteric surfactant were studied by rheological experiment.Based on viscoelasticity and interfacial tension,the polymer and surfactant were combined to form a binary compound oil removal system.Through the physical simulation displacement experiment,the injectivity of the system was explored,the matching relationship between the binary system and the formation porosity was studied through the analysis of the core pore structure,and the oil displacement performance of the binary complex system was studied through a variety of physical models.Finally,the injection scheme of the block was optimized by mathematical model.The results show that polymer TA2 has a strong viscosifying ability and a good synergistic effect with amphoteric surfactant ES.Although polymer TA2 affects the adsorption of amphoteric surfactant ES on the oil-water interface,it is beneficial to the stability of emulsified crude oil.Core flow experiments and analysis of structure characteristics in cores show that formations with permeability between 50×10^-3 and 500×10^-3μm²,when the concentration of polymer TA2 increases from 0.05%to 0.1%,the hydrodynamic radius of the polymer is up to 16μm,which increases the adsorption and retention of the polymer in the porous media,resulting in difficult injection.The results of physical simulation of oil displacement show that the effect of oil surfactant waterflooding is poor.When polymer flooding with different viscosity is adopted,the ability to enhanced oil recovery of polymer solution with low viscosity is poor,and the effect is greatly improved when the viscosity ratio between polymer and crude oil is greater than 0.2.However,the injection capacity of polymer solution with higher viscosity is limited.With the addition of polymer,the sweep efficiency of the system is improved,and the recovery increases with the increase of polymer concentration.This profits from the increase of polymer’s seepage resistance in the hyperpermeability core,which leads to the fluid flow direction of the oil displacement system,thus improving the utilization degree of the low-permeability core.Combined with the numerical simulation of enhanced oil recovery in the study block,the results show that,among the three development methods of surfactant flooding,binary combination flooding and multi-slug flooding,the binary combination flooding has the highest incremental oil production（up to 3797 m³）and the best economic benefits.