Investigation of the Transport Characteristics of Heavy Oil–Water Ring in Horizontal Straight Pipes through Numerical Simulation and Orthogonal Experimentation

Abstract

Heavy oil–water loop transportation technology has emerged as one of the most significant solutions for energy-efficient utilization globally. However, this technology encounters several challenges, particularly in accurately identifying the key factors that influence the stability and pressure gradient of heavy oil–water ring transport. This study analyzes the impact of critical factors, such as density difference, viscosity difference, oil–water flow rate, and interfacial tension, on the pressure gradient and flow stability within heavy oil–water ring transportation pipelines through numerical simulations. Additionally, an orthogonal test is employed to quantitatively evaluate the significance level of these four factors concerning the pressure gradient and eccentric stability index. The results indicate that a smaller density difference between oil and water leads to less disruption of the core-annular flow structure and, consequently, results in a lower pressure gradient value. When the viscosity of heavy oil falls within a specific range, variations in the oil–water viscosity exert minimal influence on the water ring stability but have a more pronounced effect on the pressure gradient. The flow rate of oil–water is crucial for maintaining stable core-heavy-oil flow toward the pipeline’s end; reduced flow rates increase the likelihood that core-heavy-oil will come into contact with pipe walls, thereby elevating both pipeline pressure gradients and diminishing water ring stability. Furthermore, while changes in interfacial tension have negligible effects on the water ring stability, an increase in interfacial tension correlates with an increased pressure gradient. Through orthogonal test analysis, it was determined that among these factors, the density difference exerts the most significant influence on both pressure gradient and stability; this is followed by flow rate and viscosity differences. In contrast, interfacial tension demonstrates a minimal impact relative to other variables.