Efficient Preparation of Nano-Starch Particles and Its Mechanism of Enhanced Oil Recovery in Low-Permeability Oil Reservoirs

As development of low-permeability oil reservoirs continues to increase, it urgently needs an efficient enhanced oil recovery (EOR) technology to adapt to the new situation and requirement of oilfield exploitation. Although the application of nanomaterials for the EOR of low-permeability oil reservoirs has initially obtained good results, the types of currently used nanomaterials in the field of EOR are limited, and the mechanism of EOR is still unclear. In this paper, a type of nanosized starch particle is efficiently prepared using the method of precipitation with the help of ultrasonic oscillation. Under ultrasonic oscillation, the viscosity of starch paste can be significantly decreased, which is beneficial for the precipitation of starch nanoparticles. After ultrasonic oscillation, the size of the developed nanoparticles is smaller and controlled during the precipitation of starch paste using ethanol as the precipitating agent. The developed nanosized starch particles are suitable for the low-permeability oil reservoirs with low-salinity water. Subsequently, the mechanism of EOR of the developed nanosized starch particles is systematically studied through laboratory experiments. In addition to changing the wettability of rock surface and decreasing oil/water interfacial tension (EFT), the nanosized starch particles can effectively change the motion state of water molecules and cause the change of the structure of water molecules. In the low-permeability core, the displacement front of the nanosized starch solution is uniform, and the sweep volume of the nanosized starch solution flooding is large. Because of a higher sweep volume and a smaller adsorption loss, nanosized starch solution flooding can achieve a better effect of oil recovery than surfactant flooding in 30m of low-permeability porous medium. The conclusions can provide a new guidance for EOR technology to support the efficient development of low-permeability oil reservoirs.