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

Small Carbonate Scaling Tendency 
If the scaling problem is assessed to be small (i.e. slight carbonate 
supersaturation and low water volume), then infrequent acid washing of 
production tubing and safety valves may be sufficient. 
More Severe Carbonate Scaling Tendency 
However, if the scaling problem is assessed to be more severe, with a higher 
supersaturation with respected to carbonate, and if the water volume is higher 
(say, > 1,000 bbls per day), then the frequency of acid jobs would probably be 
too high to be economic and the risk of safety valve damage would also be too 
high. 
At this stage, a final acid job should be carried out to remove any existing 
deposited carbonate scale and then a chemical scale inhibitor should be 
applied as a “squeeze” treatment into the formation and this should provide 
longer-term protection. 
The duration of the effectiveness of a squeeze treatment (the squeeze lifetime) 
is dependent on produced water volumes and various other factors, but ranges 
from 6 to 24 months. 
Severe Carbonate Scaling Tendency 
If the carbonate problem is severe, but is only located in the topside facilities, 
then it is recommend that scale inhibitor be continually injected at an 
appropriate point within the production facilities; preferably at the well head, or 

---

TOPIC 2: Oilfield Scale 
 
 
 
33 
©H
ERIOT
-W
ATT
U
NIVERSITY B41OA December 2018 v3 
below the subsea safety valves (this is to protect the safety valves and the 
topside facilities from carbonate scale build up). 
General Comments on Different Carbonate Treatments 
The advantage of the chemical scale inhibitor treatment is that they give longer 
protection than acids jobs which are intended just to remove the problem. 
If it is predicted that the well will experience seawater breakthrough, then the 
application of an inhibitor squeeze will protect the well during the initial 
breakthrough period when the exact extent of the problem may be reviewed. 
The build-up of scale within facilities can then be measured topside by using 
thermography. The investigation of scale downhole can be conducted with 
calliper and gamma logs (gamma log will not show a positive response to 
carbonate scale) and also with downhole video equipment to avoid confusion 
between casing collapse and mineral deposit build up.