Viscosity-reducer flooding is an effective method to improve oil recovery after the water flooding of heavy oil, and water-in-oil emulsion (W/O emulsion) is easily formed during this process. W/O emulsion has a strong ability to improve mobility ratio and block off high permeability layers, which can effectively improve sweep coefficient and enhance oil recovery. The microscopic visual glass model is mainly used to study the microscopic oil displacement mechanism of dilute oil; however, there are few studies on the emulsification mechanism and influencing factors of heavy oil. The purpose of this paper is to study the mechanism of heavy oil emulsification caused by viscosity reducer at the microscopic level, and the effect of emulsification on heavy oil recovery. The visible physical experiments with the glass microscopic models with different permeability and pore sizes were carried out to study the mechanism and main controlling factors of emulsification and the oil displacement effect of viscosity reducer. On this basis, the software was used to calculate the oil recovery in different areas of the model in different flooding stages, which provides a more intuitive understanding of the oil displacement effect of viscosity reducer. The results showed that there are mainly three types of emulsifications between pores: pore throat-breaking emulsification, blind-end emulsification, and pore channel extrusion emulsification. Hence, the mechanism of the three types of emulsifications and the relationship between droplet size with shear stress have been explored. The shear stress increased with the increase of the shear rate, and the oil droplet size in the model decreased with the increase of the shear. The blocking mechanism of pore throat and the shearing action of viscosity-reducer solution are the main mechanisms of viscous oil emulsification between pores. Generally, the particle size of the emulsified oil droplets formed by the blocking action is large, and it is easy to form pore throat emulsion. The particle size of emulsified oil droplets formed by shearing of viscosity-reducer solution is small. When the pore diameter is smaller than the particle size of oil droplets, the mobility of oil droplets between pores is poor, which means the oil droplets easily accumulate at the blind end to form residual oil. From the results of viscosity-reducer flooding experiments, the heavy oil recovery in each area of the model has been significantly improved after viscosity-reducer flooding compared with water flooding, with the recovery factor in the edge area of the model improving by up to 24.22%. The viscosity-reducer solution has a significant displacement effect on the residual oil in the edge area of the model.

As driven by the increase in global fuel demand and decrease in worldwide reserves of conventional oil, it is important to develop new production technologies for heavy oil. In this work, copolymers PAAI₇, PAAI₁₀, and PAAI₁₅ were synthesized and evaluated as potential viscosity reducers for heavy oil. iso‐Tridecyloxypolyethylene glycol acrylates (I13C_xAA, x = 7, 10, 15), acrylic amide (AM), and 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) were polymerized to give the copolymers PAAI_x, respectively. Copolymers PAAI_x were characterized by FTIR, ¹H NMR spectroscopy, and TGA and showed good thermal stabilities as the decomposition temperature was above 350°C. Their viscosity‐average molecular weights were measured as in the range between 6.53 × 10⁶ and 10.58 × 10⁶ g/mol. The effects of temperature, shear rate, and salinity on the viscosity of polymer solutions were studied, and PAAI_x had reasonable rheological properties. The solutions of PAAI_x in formation water could emulsify heavy oil sample to form oil‐in‐water emulsion when mass ratio of oil:water was in the range of 6:4‐2:8, respectively. The rates of reduction in viscosity of emulsions compared with that of original oil sample were 53.5%‐97.5% at 50°C under shear rate of 20 s⁻¹. The effects of oil:water ratio, emulsifying temperature, and shear rate on the viscosities of emulsions were extensively studied, and the effect of the polymer structure on the emulsification and viscosity reduction of heavy oil was also discussed. Among three copolymers, PAAI₁₅ formed the most stable emulsion with heavy oil and the emulsion had the lowest viscosity. PAAI₁₅ had the potential for further study.

With the increase of crude oil production in the world, the proportion of conventional crude oil is gradually reduced, so the recovery of heavy oil has become the development trend. Due to the characteristics of high viscosity and low fluidity of heavy oil, its exploitation difficulty is much higher than that of conventional heavy oil, which has become the main problem restricting its exploitation and utilization. In this paper, the commonly used chemical viscosity reduction technologies for heavy oil were reviewed, including emulsification viscosity reduction technology, oil-soluble viscosity reduction technology and catalytic modification viscosity reduction technology. Combined with literature and related oilfield experiments, this paper analyzed the mechanisms, advantages and disadvantages of technologies and prospected for future technology development of viscosity reduction technology.