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

Mechanical Removal Method: Waterjetting 
Waterjetting (with or without acid) is a way of physically removing scale. High 
pressure waterjetting may be very effective for removing scale, particularly 
carbonate scale from topside production tubing, but it is less effective for 
downhole scale removal due to the rapid loss of mechanical abrasion away 
from the jet point. The various circumstances where the above methods 
should be employed will be discussed later. 
2.7 Assessment of Scale Problems and Treatments 
If water is produced that has a scaling potential, how is it best handled in terms 
of scale control downhole and topside? 
In the first sub-section below, we will examine how to handle formation water 
(FW) alone. This may be produced from a field which is being naturally 
depleted, or where seawater (SW) breakthrough (in reservoirs that are 
supported by seawater injection) has not yet occurred. 
In the second sub-section below, we will examine how to handle co-mingled 
formation water and injection seawater (FW/SW). 
Each scenario, either single brine (FW), or co-mingled brine production 
(FW/SW), has its own specific problems and possible solutions. It is better to 
examine each case separately. 
2.7.1 Formation Water (FW) Only Produced 
When formation water only is produced, the scaling potential of the brine must 
be assessed using scale prediction software (e.g. OK Scale, Multi-Scale etc.). 
This takes into account the various conditions of temperature and pressure 
(T/P) across the production facilities. 
Typically, in a given assessment, we would perform scale prediction 
calculations under the following conditions: downhole T/P; wellhead T/P; flow 
line T/P; and topside T/P. 
In order to gauge the magnitude of the likely scaling problem (e.g. in terms of 
the maximum possible amount of scale that may form), the volume of water 
being produced, and its predicted production profile with time, must be 
available. 

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TOPIC 2: Oilfield Scale 
 
 
 
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NIVERSITY B41OA December 2018 v3 
This would usually come from the reservoir engineering/numerical simulation 
calculations or from other estimates. The accompanying downhole, wellbore 
and topside production conditions are also required and these would be 
derived from the production engineering calculations that would accompany 
the reservoir calculations. From this data, it will be possible to assess the 
amount of scale formation and its location, both downhole and topside. 
In the case of a carbonate scaling problem for a produced (not co-mingled) 
brine, the maximum carbonate scale will form in the topside facilities and 
wellhead region and, as the reservoir pressure declines with time, the scale 
will move down hole. 
If the pressure declines sufficiently, the carbonate scale will form below the 
safety valves and may move towards the perforations – ultimately scale may 
form in the formation. 
This is one possible broad scenario for the production of a single (not co-
mingled) carbonate-scaling formation brine. However, over this period of 
pressure decline, any injected brine may breakthrough into the producer and 
this will complicate the scale formation picture (see below).