Summary
This paper reports a challenging and unique scale-forming environment in
northern Alberta, Canada. Calcite was forming on the fire tubes in a series of
treaters. Bulk fluid temperature was 110°C, but skin temperature of the fire
tubes was in excess of 450°C. This created an extremely high scaling
potential.
The paper provides background on the field case history with a detailed
description of the process and the scale-forming environment. An in-depth
scale-modeling study characterizing the scaling up to 200°C is provided.
Further laboratory studies are reported, including performance testing on
candidate scale inhibitors and differential scanning calorimetry (DSC) to
determine their molecular stability. The testing looked at scale inhibitors and
investigated the direct inhibition properties, as well as any dispersion
properties to prevent surface adsorption of scale on the fire tubes.
The testing found that the incumbent scale inhibitor (phosphonate based) was
a good product for the bulk scale inhibition but was not stable at the
temperature of the fire tubes. The most thermally stable scale inhibitors
tested were polymaleic acid copolymers and polymeric acrylic acids of
low-to-medium molecular weight.
No scale inhibitors were tested to be fully stable up to 450°C, but it was
found in field application that the best product identified through laboratory
testing was sufficient to delay the scale formation on the fire tubes. It is
hypothesized that the product was stable at high temperature for the residence
time of fluid in the treaters or imparted some degree of scale inhibition even
after thermal molecular scission.
The paper concludes with data of the fire-tube change-out history
highlighting the step change in performance when applying the polymeric
inhibitor quantified by change-out frequency and presence of hot spots.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
26 March 2010
- Meeting paper published:
27 May 2010
- Revised manuscript received:
19 June 2010
- Manuscript approved:
11 August 2010
- Published online:
22 April 2011
- Version of record:
1 September 2011
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