Removal mechanism of adhering heavy oil from pipeline wall in low-temperature flow

With the global emphasis on heavy oil development and increasing water content in Chinese oilfields, the low-temperature flow of heavy oil has been widely concerned. Integrating experiments and theoretical modeling, a hydrodynamic balance model for removing adhering heavy oil from pipeline wall was proposed to determine the temperature threshold for heavy oil transportation (adhesion temperature, AT). Two forms of heavy oil removal from pipeline wall were identified in the study: slide and lift-off. At low temperatures, the abrupt increase in wall-adhesion mass is primarily due to the inability of oil droplets to be removed through lift-off, but rather only through slide. Therefore, the temperature marking the transition from lift-off to slide is suggested as the AT criterion. Predicted AT values were in effective concordance with experimental values, with a maximum deviation of 3.78 °C. ATs for oilfields were predicted, and field cooling transportation tests showed no significant pressure drop increase, indicating the model's practical applicability. Additionally, the influence factors of the model were analyzed based on considerations of adhesion force and hydrodynamic removal force. This study aims to reduce heating energy consumption and carbon emissions during transportation under the premise of ensuring safe flow of high water-content heavy oil.