Research Preparation And Evaluation On Nano-scale Relative Permeability Modifier In Low Permeability Reservoir According Changed Permeability Mechanism

The carbonate reservoirs with low permeability in China generally need to improve the oil and gas in the matrix and the seepage in the cracks to ensure the efficient development by improving permeability.Relative permeability modifiers?RPMs?can greatly reduce water phase permeability and have little effect on oil phase permeability in reservoir to achieve water control and enhance oil production.The traditional RPMs system is generally a polymer water-soluble polymer or weak gel system,mainly used to block oil and gas reservoirs with high permeability,large pores and fractures.Nano-SiO₂ RPMs systems have the advantages of surface,volume,quantum size effect and etc.They can enter the micron and nanometer pores and throats and then the nano-film was formed,and thus this plays a role in improving the oil and water phase permeability to achieve the highly efficient development of low permeability oil reservoirs.This paper systematically summarizes the system and effect of nano-SiO₂ which used in the improvement of the oil and water phase permeability in domestic and foreign oilfield,and analyzes the principle of it from the theoretical point of view.Then it points out the problems and trends in the process of research on the preparation,evaluational system,mechanical analysis and applicational promotion of the nano-phase relative permeability modifiers.In this paper,the nano-phase relative permeability modifiers were prepared by single factor and mixed orthogonal experiment and can exist at least about 3 months without layering,which took the diesel oil with dispersed nano-SiO₂ as the oil phase,the aqueous solution of NaCl as the water phase,the Span 80 and Tween 80 as the emulsifier and the isobutanol as the co-emulsifier.Then the structure was observed with a microscope and characterized by infrared spectroscopy and the particle size was measured by a nanometer particle size analyzer.At last,the effect of nano-SiO₂ content on its properties was also studied.The results show that the micro-image of the modifier is a water-based nanoemulsion in the form of spherical droplets.The infrared spectra show that there are hydrophilic groups and a large amount of Si-O-Si hydrophobic groups.The average particle size of the particles is 4.065nm.With the increase of nano-SiO₂ content,the average particle size of the particles stay 3⁷nm;the viscosity increases;the surface and interfacial tension firstly increase and then decrease;And the average contact angle on the carbonate pellets is between 40°and 75°.The adsorption and flushing resistance performance of the modifier is better than other modifiers.The decrease of oil phase permeability and relative permeability in the carbonate core is below 20%,and the decrease of water permeability and relative permeability is above80%after the treatment by nano-phase relative permeability modifiers.The presence of hydrophilic groups in the improver is beneficial for the droplet to disperse uniformly into the medium water and firmly adsorb on the surface of the hydrophilic rock.The existence of hydrophobic groups can form a stable nano membrane structure,which will change the wettability of the rock and affect the oil and water permeability.