B41oa oil and Gas Processing Section a flow Assurance Heriot-Watt University

3.3 Problems Associated with Wax Formation 
Crystallisation of waxes in crude oil produces non-Newtonian flow 
characteristics including very high yield stresses. Wax crystallisation depends 
on the degree of subcooling (i.e., temperature below the wax phase boundary) 
and the cooling rate. 
Wax crystallisation in crude oil pipelines may cause the following three 
problems: 
•
High viscosity leading to high pressure losses. 
•
High yield stress for restarting the flow. 
•
Deposition of wax crystals on pipeline wall, which could result in higher 
pressure drops and in some cases complete blockage. 

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TOPIC 3: Wax Deposition 
 
 
 
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NIVERSITY B41OA December 2018 v3 
3.3.1 Pressure Loss; High Viscosity 
High viscosity and wax deposition on pipe surfaces are major reasons of high 
flowline pressures – the crystallisation of wax suddenly increases crude fluid 
viscosity due to the gel forming tendency of the crystals. 
Another factor, leading to an increased pressure loss (and a reduction in 
effective capacity of the line), is the deposition of wax on the pipe wall. This 
both reduces the effective pipeline diameter while, at the same time, increases 
the pipewall roughness. 
Sometimes the increase pressure loss (and the reduction in flow capacity) may 
cause crude transportation to stop altogether. The mechanism here is that 
high pressure loss across the tubing causes: low flow rates of the well; this in 
turn leads to lower temperature; thus, the conditions for wax deposition are 
more favourable (because of reduced fluid temperature); further reductions in 
flow rate and temperature can follow – eventually production may stop.