| Low-permeability reservoirs have the characteristics of small porosity,small pore throat and poor percolation ability,which cause problems such as poor water flooding effect,high water content and low recovery.In general,chemical flooding is used to improve oil recovery.However,conventional chemical flooding has a large number of problems,and nanoparticles can better enter the pores of low-permeability formations and change the wettability of rocks.It has caused widespread concern.Because of its small particle size,large surface activity and strong adsorption,nano-titanium dioxide has potential for the application of nanoparticles in the direction of enhanced oil recovery in low permeability formations.In order to enhance the stability of nano-titanium dioxide particles,reduce the agglomeration between particles,improve the migration ability of particles in pores,and change the wettability,some methods are used to modify nano-titanium dioxide particles.Through various test analysis,the physical and chemical properties of the modified nano-titanium dioxide particles were evaluated to determine the suitable formation environment.Finally,through the one-dimensional core simulation flooding experiment,the oil displacement experimental parameters are optimized,the oil displacement effect is evaluated,the permeability limit in the core is determined.The modification experiments show that when the molar ratio of reactant is 1:1,the reaction temperature is 60?,and the reaction time is 6 h,the nano-titanium dioxide particles have the best suspension in water,and can be stably left standing for several weeks without agglomeration;The product structure is characterized by infrared spectroscopy,scanning electron microscopy and thermogravimetric analysis;The static experiment results show that the average particle size of the modified sodium-titanium dioxide particles is 246.7 nm,and the Zeta potential values are mainly distributed at-47m V and-30.6 m V.The modified nano titanium dioxide particles are suitable for the mineralization degree of the formation water of 0?20000 mg/L,the formation temperature is 40??60?,the formation water p H is 2?8,the sodium ion concentration is less than 1000 mg/L of sulfuric acid Sodium water type,sodium bicarbonate water type and magnesium chloride water type with magnesium ion concentration lower than 1500 mg/L;The contact angle of titanium dioxide increases fromto,and the particles change from strong hydrophilic to weak hydrophilic;The modified nano-titanium dioxide particles can effectively reduce the interfacial tension value to 0.74 m N/m.The oil displacement experiment shows that when the concentration of the nano-displacement system is 0.1%and the injection amount is0.3 PV,the injection method with alternating injection is used,and when the timing of injecting nanoparticles is 98%,the maximum recovery rate is 18.18%.When the core permeability range is 5×10-3?m2?20×10-3?m2,the enhanced oil recovery is better,reaching 11.11%?12.73%.In this paper,the oil displacement mechanism of nano-titanium dioxide particles in low-permeability reservoirs is initially formed,and a complete nano-titanium dioxide particle displacement system is constructed to provide theoretical and practical basis for further application of the mine. |
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