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

3.4.1 Wax Constituent Analysis 
Determining wax and fluid composition is very important in terms of assessing 
potential wax problems. It is also important in terms wax mitigation efforts. The 
advance in analytical tools, such as gas chromatography (GC), now makes the 
compositional analysis of wax deposits possible. 
Cold rods, or fingers, can be inserted into a fluid sample and the deposited 
wax may then be collected for analysis. The properties of these rod deposits, 
as well as in-situ flowline deposits, were analysed using GC (Newberry et al., 
1986): 
•
The rod deposits have molecular weight ranges that correspond to 
carbon number between C
18
to C
66
– the peak concentration occurs at 
C
38
. 
•
The flowline deposits have carbon number ranging from C
18
to C
60
– 
the peak concentration occurs at C
30
. 
•
Gas chromatograms of wax collected from pig receivers in the North 
Sea (pigs are used to remove wax deposits from pipelines), show that 
hydrocarbons ranging from C
30
to C
60
– these are the major 
compounds taking part in wax precipitation (Labels-Carrier et al., 
2002). 
Wax precipitated from crude oils is composed mainly of paraffins. It is reported 
that n-paraffins were the principal constituents of petroleum wax (Sarivastava 
et al., 1993). 

---

TOPIC 3: Wax Deposition 
 
 
 
8 
©H
ERIOT
-W
ATT
U
NIVERSITY B41OA December 2018 v3 
The constituent analysis of wax, experimentally generated from North-Sea 
condensate oils, showed that iso-paraffins were the most abundant fraction. In 
addition, n-paraffins and naphthenes contributed considerably to wax deposits. 
However, little in the way of aromatic species were found in these deposits 
(Pedersen et al., 1991). 
Furthermore, the relative amount of iso-paraffins versus n-paraffins increased 
with the temperature reduction. However, due to the limitation of experimental 
techniques (i.e., HTGC/MS), it was impossible to determine which 
hydrocarbon class dominates during the initial wax crystallisation period. 
The compositions of petroleum wax obtained from different sources (such as 
pipeline pigging devices, crude oil storage tanks and wax samples centrifuged 
from the discharge of pump stations) were all analysed (Roehner et al., 2002): 
•
Wax obtained from the pipeline pigging devices demonstrates a high 
ratio of n-paraffin versus non-n-paraffin. 
•
All wax obtained from different sources show considerably higher ratios 
of n-paraffins/non-n-paraffins compared to the crude oil. 
•
Compositional analysis of wax obtained from the centrifuged samples 
at different temperatures show that lower temperature leads to higher 
proportion of non-n-paraffins.