Effect of crude oil self-emulsification on the recovery of low permeability reservoir after well soaking

The emulsification phenomenon exists during crude oil exploitation in the Jimsar area of Xinjiang. In the field, the emulsification mechanism and its influence on production are unclear. To clarify the self-emulsifying law of crude oil and its influence on production during soaking, this study carried out microscopic visualization displacement experiments, spontaneous imbibition displacement, and oil-water displacement experiments. Results show that oil-water contact time and water phase type affect the size of the emulsified layer between crude oil and water phase. The oil-water distribution type affects the formation mode of crude oil emulsification. After the opening of the water phase channel, crude oil mainly migrates in the form of a water-in-oil emulsion. The crude oil attached to the pore wall and stuck in the pore throats is the main source of the dispersed phase in the emulsion. When crude oil moves through pores, the high-curvature boundary changes the interfacial tension and capillary force. Thus, this case makes the crude oil easily stuck to form small oil droplets and promotes the dispersion of crude oil to form an emulsion. In the tight core, a decrease in the spontaneous imbibition ability was attained by increasing nano-emulsion concentration. However, the oil displacement effect of 0.3% nano-emulsion is better than that of the 0.6% concentration. Therefore, ensuring a certain spontaneous imbibition ability and a certain displacement efficiency is necessary. Oil recovery can be enhanced to a certain extent after self-emulsification in the pores of Jimsar crude oil. When oil displacement depends on the capillary force or driving pressure difference, the oil-water interfacial tension is not the lower, the better, and a suitable range exists. The suitable oil-water interfacial tension in this region is between 0.1 and 1 mN/m.