With the depletion of conventional light crude oil, heavy
crude
oil will occupy an increasing share of the energy structure in the
21st century. Heavy crude oil is characterized by an API gravity of
10 to 22.3 or a viscosity of 0.09 to 10 Pa·s. The flow of heavy
crude oil in the pipeline is laminar in the higher viscosity range
and turbulent in the lower viscosity range, and its flow resistance
comes from the viscous force between the oil and the wall or the additional
stress of turbulent flow. Hence, pipeline transportation of heavy
crude oil is faced with a huge loss of frictional resistance, which
means a reduction of the transportation efficiency. To decrease pump
power consumption, improving the transportation efficiency of heavy
crude oil pipelines is a key factor. In recent years, some biomimetic
technologies that reduce the flow resistance of viscous oils have
made new progress in improving their fluidity and have not yet been
put into use in commercial pipelines. Therefore, it is important and
appropriate to discuss the breakthrough achievements and progress
made by researchers in the drag reduction (DR) of heavy crude oil
and to summarize its advantages, disadvantages, and potential problems.
This review discusses boundary layer control methods for heavy crude
oil drag reduction. First, conventional DR technologies, such as polymers,
surfactants, fiber suspensions, oil–water core annular flow
(CAF) and oil–aqueous foam CAF, and potential DR technologies,
including oleophobic surfaces, flexible walls, biomimetic microgrooves,
and ferrofluid annular DR under magnetic confinement, are presented.
Second, the mechanism of DR is investigated and summarized; the highlights
and progress of the technology are reviewed, and new ideas to improve
the existing DR technology are proposed. Finally, the challenges and
prospects of DR are presented.