Study And Evaluation Of Microemulsion System For Ultra-Low Permeability Oil-Gas Resources

The hydrophilic sandstone core wettability is important to flood development which received general concern. Influx water flowback and oil and gas recovery both improved when the rock in the intermediate or weak water wet. Study on the adsorption rules of double chained cationic surfactants and non-ionic surfactants on the hydrophilic sandstone core by atomic force microscope, based on the study of micro-emulsion, pseudo-ternary micro-emulsion consisting of micro-emulsion/water/diesel oil, a micro-emulsion was developed and used to alter the wettability of the hydrophilic sandstone core.The experimental results showed that Gemini occurred monolayer adsorption with little bilayer absorption on the mica surface, the reversal wettability occurred at the high and low concentration of Gemini on the surface of hydrophilic sandstone. Moreover, the concentration had little effect. It was deduced from the absorption morphology obtained by AFM. The behavior of Gemini adsorbed in sandstone core conformed to the Langmuir isothermal adsorption curve. Saturated adsorption and the quality of sandstone turned into good linear relationship. At the same time, the electric charge of sandstone core was changed from negative to positive by Gemini, and increased with the concentration of Gemini continuing to rise and finally keep stable.OP mainly occurred monolayer adsorption in low concentrations, bilayer absorption when high concentration, whether monolayer or bilayer adsorption, OP can’t significantly improve the wettability of hydrophilic sandstone core. The behavior of OP adsorbed in sandstone core also conformed to the Langmuir isothermal adsorption curve. But, the saturated adsorption of OP was smaller than Gemini’s.Eventually optimized micro-emulsion system for the ultra-low permeability reservoirs based on the pseudo-ternary micro-emulsion:MA and MB. Study the main properties of micro-emulsion system and the influence of wettability on the low permeability water-wet sandstone core, research showed that micro-emulsion system in lower concentration can improve the low permeability water-wet sandstone core wettability for Intermediate or weak water wet (65°<contact angle<90°). Micro-emulsion system solution have lower surface tension, which is30mN/m, it can help reducing the capillary force, working fluid to flowback to avoid damaging the formation and achieve the stable effect of low permeability oil and gas well production. The using temperature of micro-emulsion system aqueous solution was130℃or so and resistance to salinity, meeting the high temperature and salinity requirements of developing the low permeability reservoir. Micro-emulsion system and fracturing fluid or its additive was good compatibility. The experimental results of laboratory evaluation show that:flowback rate can be reduced, antiswelling rate can be effectively improved and the damage of permeability can be reduced. The micro-emulsion system for low permeability oil-gas resources is simple to prepared, which ideally improved wetting ability on the hydrophilic sandstone core and aqueous solution can dissolve in oil, with low interfacial tension, very promising.