Preparation And Properties Of Perfluorooctanoyl Gas-wetting Nanomaterials

Reservoir wettability is a very important factor that affects the migration of oil and gas in the formation.In the development of oil and gas reservoirs,the liquid in the bottom hole area or the reservoir flow channel is retained in the hole roar to form a"liquid lock effect"phenomenon.As a result,the permeability of the reservoir and wellbore is reduced,resulting in a serious decline in productivity.To solve this problem,some scholars have proposed to alter the wettability of the reservoir surface from liquid-wetting to gas-wetting,which can enhance the fluid flow capacity in the reservoir channel.However,the existing gas-wetting alteration agent has poor gas-wetting on core,and only achieves gas-wetting or neutral gas-wetting,but cannot realize strong gas-wetting.In this paper,nano-particles with high surface activity and high specific surface area are used to prepare super/strong gas-wetting nanomaterials that can significantly improve oil and gas recovery.The migration rules and mechanism of gas,water and oil three phases in gas-wetting porous media were studied,which has important guidance and application value for improving oil and gas recovery.In this paper,five kinds of N-perfluorooctanoyl small-molecule gas-wetting alteration agents were synthesized through amidation reaction.The structure was characterized by nuclear magnetic and infrared spectroscopy,and the reaction conditions were optimized by response surface methodology.The properties of gas-wetting alteration were evaluated by contact angle method,Owens two-liquid method,glass capillary tube and imbibition test.The results show that the average contact angle of oil and water on the core surface can reach 105°and 120°,and the surface free energy is reduced from 68.4 m N·m^-1 to approximately 10 m N·m^-1.It can maintain good gas-wetting alteration performance at a high temperature of 160°C,high-valence inorganic salt ions(8000 mg·L^-1)and a p H value of 5-9.Moreover,elemental analysis showed that fluorine was detected on the surface of the core,indicating that the gas-wetting alteration agent was adsorbed on the surface of the rock and played a role of hydrophobic and oleophobic.However,the synthesized small molecule gas-wetting alteration agent cannot achieve super/strong gas-wetting performance.Therefore,the gas-wetting alteration agent was grafted onto the surface of silica,microcrystalline cellulose and graphene oxide nanoparticles through esterification reaction,and three kinds of gas-wetting nanomaterials that can alter the core surface into super/strong gas-wetting were formed.The structure,particle size and thermal behavior were characterized by infrared spectroscopy,photoelectron spectroscopy,laser diffraction particle size analyzer and thermogravimetric-differential calorimetry.It is found that the modified silica material has the best gas-wetting alteration performance,which can increase the contact angles of the oil and water to 157°and 145°,respectively,and the surface free energy is rapidly reduced to 0.23 m N·m^-1.It is mainly due to the enrichment of silyl hydroxyl groups on the surface of silica,which can fully undergo esterification reaction with the modifier and increase the grafting rate.Elemental analysis,scanning electron microscopy,and 3D surface profile were performed to study the gas-wetting alteration mechanism of gas-wetting nanomaterials.The fluorine content on the core surface after the treatment with silica nanomaterials increased from 0 to 7.86%,and a composite structure adsorption layer with higher roughness was formed.Therefore,the surface fluorine content and the surface roughness were increased through the gas-wetting nanomaterials,thereby realizing the alteration of the core from liquid-wetting to super gas-wetting.The displacement experiment was performed after the core was treated with gas-wetting nanomaterials,which showed that the core surface inversion to gas-wetting can reduce the displacement pressure and improve the displacement efficiency.The migration law of water and oil in gas-wetting porous media was studied by microscopic visualization displacement experiment.The results show that the gas-wetting nanomaterial is adsorbed on the surface of the core and its wettability is altered from liquid-wetting to super/strong gas-wetting.The"liquid lock effect"phenomenon in the hole roar is eliminated to improve the liquid flow ability.Therefore,the super/strong gas-wetting porous media is more conducive to the improvement of fluid flow and migration capabilities.