Model for wax inhibitors
The effec on wax appearance temperature, pour point and viscosity have been measured of 12 different chemicals that may potentially act as wax inhibitors or pour point depressants.
Precipitated wax has a substantial influence on the viscosity of oil transported in sub-sea pipelines. At high amounts of precipitated wax the pour point may be reached. This is the temperature at which the oil will gel at shut-down conditions. It is very difficult to restart a pipeline filled with an oil below its pour point. Precipitated wax may also influence the flow pattern at temperatures above the pour point. The viscosity may increase by a factor of several hundred due to the precipitated wax. This has a pronounced influence on the pressure drop in the pipeline. The flow behavior is further complicated by the fact that the viscosity behavior may change from Newtonian to a non-Newtonian. That means that the viscosity becomes dependent on the flow rate. Calsep has in cooperation with Statoil developed a shearrate dependent model for description of viscosity of oils with precipitated wax. To overcome the problems related to transport of waxy oils, wax inhibitors are often added to decrease the viscosity effect of precipitated effect and in particular to decrease the pour of the oil. Statoil in Stavanger is in the position of a comprehensive data material for the viscosity of oils with and without wax inhibitors. Statoil has agreed to make this data material available to Calsep for use in the actual EFP project. One of the aims of the project is to clarify the fundamental mechanisms behind wax inhibition. The final model will be incorporated into Calsep's commercial simulator for flow of waxy oils in pipelines. This simulator is currently mainly being applied to simulate the pressure drop in a pipeline as a result of wax deposition on the inner pipe wall
Solid wax partides may have a pronounced influence on the apparent viscosity of oil mixtures. Just a few degrees below the wax formation temperature a dramatic increase in viscosity may be seen in offshore pipelines transporting wax crude oils. The viscosity pattern is further seen to change from Newtonian (independent of flowrate) to non-Newtonian. The highest viscosities are seen for lowest flowrates, which can be troublesome in shutdown situations. Not only may the fluid be cooled down during shutdowns, but the highest possible viscosity will be experienced at startup because there is no flow. It is therefore desirable to be able to suppress the viscosity effect by addition of chemicals. The effec on wax appearance temperature, pour point and viscosity have been measured of 12 different chemicals that may potentially act as wax inhibitors or pour point depressants. In general these chemicals only marginally influence the wax appearance temperatures whereas some have a pronounced effect on the pour points and the apparent viscosity. The viscosity data suggest that the inhibitors, probably by some kind of steric hindrance, delay the solidification of wax molecules of a given molecular size. they do not precipitate at the equilibrium temperature but at a temperature 15-20 deg. C belov that. It is shown that this mechanism can be modeled by assuming a decrease of the melting temperature of the affected molecular range of wax molecules
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Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Statoil A/S |
Contact
Gl. Lundtoftevej 7
DK-2800 Lyngby, Denmark
Christensen, Peter (civ.ing.), 45876646, info@calsep.com
Øvr. Partnere: STATOIL, Stavanger (NO)
