Experimental Study and Molecular Dynamics Simulation of Oil Displacement Using Different Microemulsions in the Fang2 Block of Songfangtun Oilfield

After many years of mining in the Fang2 block of the Songfangtun oilfield, the conventional water drive development method can no longer meet the requirement of greatly improving the recovery rate, and ternary composite drive (TCD) technology is adopted for this purpose. TCD is one of the most important methods to further improve crude oil recovery, and it has entered the industrialization and promotion stage, but there are still problems of fouling in the injection and extraction system and high production and maintenance costs. In order to reduce formation damage and improve recovery in the Songfangtun oilfield, an alkali-free microemulsion system was developed by replacing the weak base sodium carbonate with sodium chloride, but its emulsification capacity was weak and the recovery enhancement value was lower than that of the weak base TCD. In order to improve the emulsification performance of the alkali-free microemulsion and enhance the effect of oil repulsion, an alkali-free microemulsion oil-repellent system was developed on the basis of the alkali-free ternary system by using the compounding of surfactant, alcohol, and sodium chloride. Through indoor physical modeling experiments, it was concluded that the SDBS alkali-free microemulsion system had the best effect on improving crude oil rheology and viscosity reduction, and the lowest interfacial tension of 9.4 × 10^-4 mN/m in the solution system when the mass fraction was 4%, with the maximum recovery rate of 47.03%, and the decrease in water content of 9.3%. Through molecular dynamics simulation and microemulsion oil-repellent coefficient, it is concluded that the alkali-free SDBS microemulsion system can greatly reduce the interaction force between crude oil and rock, with the lowest peak value of radial distribution function of 4.21, and the oil-repellent coefficient of F _p of 5.85; CMG reservoir numerical simulation software is adopted to verify the chemical repellent numerical simulation of Fang2 block, which shows that the recovery degree of SDBS alkali-free microemulsion system is 24.8% higher than that of water repellent, with the cumulative increase of 213.6 thousand tons of oil. The developed alkali-free microemulsion system not only realizes the goal of ternary composite alkalinity-free but also achieves the purpose of greatly improving the recovery rate and reducing the cost and increasing efficiency. It has a broad application prospect and can also provide a technical reference for the efficient development of other old oilfields with land-phase sandstone.