Abstract
When crude oil is extracted out of a subterranean reservoir at high temperature and pressure, it is usually transported via a pipeline, where the crude oil experiences radical changes in its physical and chemical properties, instigating numerous complications. Among the various flow assurance problems, wax deposition and build up are among the most commonly found. However, the accurate mechanism of wax deposition is still unclear and is widely debated among researchers. The mechanism under multiphase conditions is also an ambiguity. This review covers the six wax deposition mechanisms, the challenges in multiphase flow conditions, the latest types of chemical inhibitor, and a summary of factors governing chemical inhibitor performance.
Highlights
Paraffin deposition is a major problem, especially during crude oil transportation via pipelines as well as during production in the tubing string, in which the deposition of the unwanted substance causes an increase in the pressure drop [1].Paraffins are defined as a class of i-alkanes and n-alkanes that comprises a long hydrocarbon chain usually attached via single bonds
Among the six wax deposition mechanisms that have been suggested by researchers, molecular diffusion has been agreed by most researchers to be the dominant deposition mechanism [33]
It has been reported that polyethylene–polyethylene propylene (PE-PEP) and polyethylene butene (PEB) could aid in regulating the rheological properties and the size of the wax crystals in the middle distillate crude oils and fuels [110,111]
Summary
Paraffin deposition is a major problem, especially during crude oil transportation via pipelines as well as during production in the tubing string, in which the deposition of the unwanted substance causes an increase in the pressure drop (requiring higher pressure to transport the crude oil) [1]. Before the deposition of paraffin wax occurs, paraffin wax will first crystallize or precipitate out from crude oil. The paraffin wax molecules attach and detach until they reach a critical size cluster in order to be stable. These clusters are better known as nuclei, and the formation of these nuclei is defined as nucleation. The precipitation of wax can cause an increment in crude oil viscosity, the adhesion of wax to the pipe wall does not occur [9]. The precise modelling of deposition along the pipeline walls is challenging This is because the deposition of wax is a function of thermodynamic variables, hydrodynamic flow, heat and mass transfer, as well as solid–solid and surface–solid interactions.
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