Given the combination of rising global energy demand and the decline in conventional crudes,heavy crudes are generally considered to be the future energy resource.In many regions of the world,heavy crude oil must be transported through pipelines from the point of production to storage facilities or refineries.The transportation of heavy crude oil by pipeline poses serious problems related to the high viscosity and flow difficulties,particularly in cold climates or offshore conditions.Indeed,the viscosity of crude oil is an important physical property that influences and controls crude oil flow in pipelines.Viscosity introduces resistance to movement by causing a shear or frictional force between the fluid particles and the boundary walls.This high viscosity means that the pumping power requirements for crude oil in a long-distance pipeline are very high in order to overcome the increasing shear and friction forces.Therefore,in order to facilitate the pumping of these viscous oils and reduce operating expenses and the negative impact of pressure drops in pipelines during flow and processing,their viscosity must be reduced.Various techniques are used to increase pumping efficiency and improve the flow of crude oil through the pipeline,which may present logistical,technical or economic disadvantages for a given application.The main ones are the addition of surfactants or polymers,dilution with lighter crudes,use of water as annular fluid,thermal remediation and emulsification with surfactant(O/W).This review highlights the methods currently used to enhance the fluidity of heavy crude oil in pipelines behind rheology improvement,in particular the addition of additives and the use of water and surfactants to create a stable emulsion of heavy crude oil in water have been considered.
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