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

Low Specific Activity (LSA) Scale 
A further problem associated with barium sulphate scale is that it nearly 
always forms as a mixed scale containing strontium, calcium and also radium. 
Radium, which is radioactive, is an alkaline earth metal with similar chemical 
properties to barium and therefore often co-precipitates with it. 
In this way, naturally occurring radioactive materials (NORM), such as radium, 
may effectively be concentrated in the sulphate scale formation. This leads to 
radioactivity in the scale, commonly described as Low specific Activity (LSA) 
scale. 

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TOPIC 2: Oilfield Scale 
 
 
 
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The consequence of this is that more severe problems are associated with the 
removal and subsequent disposal of any such scales once formed (Payne, 
1987; Tanner, 1986; Mazzolini, 1990). 
The disposal of LSA scale is also subject to severe regulatory control and 
removal/disposal can prove expensive. This aspect is another important 
benefit in the prevention, rather than the removal, of scale formation. 
2.4 Methods of Scale Prevention and Mitigation 
This section outlines how the methods of recovery, together with the well types 
used to extract oil/gas, have a significant implication on the severity of the 
various scaling problems – these problems are encountered when water 
production occurs in an oil/gas field. 
2.4.1 Reservoir Recovery Methods 
Natural depletion 
If a reservoir is to be naturally depleted then only the formation brine/connate 
water will be produced. It is, therefore, very unlikely that sulphate scales will 
form in such a production scenario. 
However, if bicarbonate and divalent cations such as calcium, magnesium 
(and even in rare case strontium and barium) are present in high enough 
concentrations, then carbonate scale may form – leading to production 
problems. 
As already discussed, carbonate scale will form wherever the produced fluid 
pressure drops and passes through the CO
2
bubble point (typically in the 
upper portion of the production tubing and/or topside). 
Again, as discussed, in a natural depletion scenario it is possible to envisage a 
situation where the bubble point passes into the formation itself and can result 
in carbonate scale within the near-wellbore formation. 
Although carbonate scale is easier to control by acid washing and squeezing, 
the possibility of scale forming within the formation makes it necessary to 
perform squeeze treatments. 

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TOPIC 2: Oilfield Scale 
 
 
 
17 
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ERIOT
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NIVERSITY B41OA December 2018 v3