Page 175 - Handbook Of Multiphase Flow Assurance

Paraffin wax 171

A good overview of some of the experimental laboratory techniques used for wax and
waxy oils analysis is presented in Zhu et al. (2008).

Conventional techniques

The common methods for wax control include insulation, mechanical removal and chemi-
cal inhibition. The relative cost-effectiveness of each method depends on the availability and
the number of competing vendors present in a region.

Remote sensing and monitoring

Remote sensing of wax deposition is relatively difficult as the deposit is usually thin and
affects the frictional pressure drop mainly by an increase in pipe wall roughness, particularly
in multiphase flow.
The remote sensing methods for wax detection include ultrasonic measurement through a
pipe wall, optical detection and indirect methods such as a change in readings of instrumen-
tation where a wax deposit could cover and insulate temperature or pressure probe.
Technologies such as virtual metering which combine the readings from all available pres-
sure and temperature gauges in wellbore, tree and flowline may be able to detect the devia-
tion in pressure drop from normal, which may be indicative of wax deposition. Such remote
monitoring should be done with a complete analysis of the possibility of other solids or liq-
uids accumulation which may affect the pressure drop in a monitored section of production
system.

Emerging techniques

The method of magnetic treatment of oils to reduce the deposition of wax has been dis-
cussed for over 50 years. The method is not 100% reliable despite field data sets which show
its effectiveness in some wells. The method may affect kinetics of wax crystallization, similar
to the cold flow technique, promoting precipitation of wax as crystals in flowing produced
fluid and effectively decreasing the amount of n-paraffins dissolved in oil and available for
deposition in wells and flowlines. The method reportedly is only effective in waxy oils where
polar components such as flocculated asphaltenes are present. As this method does not pro-
vide a complete reliability, it found little commercial application in the field.
Jetting using coiled tubing has been in use for several years to clear and decommission un-
scrapable subsea pipelines plugged with wax. A plugged subsea line is usually cut and raised
to surface, one end at a time, for cleaning with a coiled tubing jet.
Pressure pulsation for wax remediation has also been used with recent success. Wax block-
age gets displaced from a pipe. Adequate downstream storage should be provided to capture
the displaced wax.

Modeling

Historic scraping models are based on flowloop tests performed with dead oil. Wax ages
in field pipeline differently than in a laboratory flowloop. Fluids in multiphase flowlines
are “live” and behave very differently from “dead oil” or stock tank crude as shown in
Figs. 5.37–5.39.
A proper scraping model should be based on a balance of forces acting on the scraper so
that the scraper does not get stuck. These include the friction of scraper on the pipe wall,