Research on molecular mechanism and prediction model of viscosity reduction of heavy oil by different types of gas

ABSTRACT

Dissolved gas flooding techniques are widely used in the later stages of heavy oil reservoir development. The role of foam oil in enhancing oil recovery from heavy oil solution gas has been researched. However, it is difficult to analyze the molecular mechanism of foam oil in the dissolved gas property theory and viscosity prediction model proposed by other scholars. In this study, the microscopic mechanism of the interaction between gas molecules and heavy oil molecules in foaming oil was analyzed by the variation of bubble point pressure and viscosity of different dissolved gases (CO₂, N₂, CH₄) in heavy oil samples. By comparing the variation of bubble point pressure of different dissolved gas samples, it was found that the interaction between gas molecules and heavy oil molecules seriously affected the solubility of gas in heavy oil at the same temperature and pressure. An increase in the solubility of the gas in the dissolved gas sample of heavy oil increases the bubble point pressure. The factors influencing the viscosity of heavy oil show that pressure has the least effect on the viscosity reduction of dissolved gas. The higher the concentration of dissolved gas, the more pronounced the viscosity reduction effect. However, the viscosity reduction performance of the dissolved gas in heavy oil became less effective as the temperature increased. Samples A, B, and C, at 15 mol% CO₂ concentration, the dissolved gas viscosity reduction effect decreases by 13.75%, 9.7%, and 12.2% when the temperature is increased by 40°C. In addition, samples A, B, and C, at 50°C and 10 mol% gas solubility, the viscosity reduction effect of CO₂ is 25.6%, 8.6%, and 19.7% lower than that of N₂. Based on the influencing factors of viscosity reduction of heavy oil dissolved gas, this study modified the FJ viscosity prediction model and proposed a physically meaningful heavy oil viscosity prediction model. The model predicts the viscosity of heavy oil dissolved gas with over 90% accuracy (R² > 0.9) and has some applicability to mixed component gases.

KEYWORDS:

• dissolved gas
• bubble point pressure
• viscosity of heavy oil
• dissolution mechanism
• expansion and viscosity reduction mechanism
• viscosity prediction model

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Research on Phase Characteristics of High Temperature and High-Pressure Complex Fluids and Solid Phase Deposition Law 2021DJ1001”, a fundamental prospective project of China Petroleum. National Natural Science Foundation of China: Nanometer scale liquid-solid interface and flow mechanism during in-situ conversion of shale oil; Approval No.: 42102163