An operator in West Africa required a scale inhibitor for an application with several technical challenges. The scale inhibitor was required to meet the Angolan decree on environmental acceptability, had to be compatible with F22 alloy present in the wellhead, and had to be suitable for application via umbilical. The scale in question was a reasonably harsh barium sulphate condition. A number of chemical formulations were suitable for use with F22, however, these chemicals did not meet the performance requirements set for barium sulphate inhibition.

Testing was conducted starting with corrosion tendency screening, whilst several potential raw materials were checked for their environmental credentials. It was possible to meet the corrosion screening conditions set by the operator with one raw material; however, this did not meet the scale inhibition criteria. Several chemicals were examined in dynamic scale loop testing, with none achieving the required performance. It was decided to evaluate blends of generic scale inhibitors, to assess whether a synergy between two different chemicals could offer improved inhibition performance, whilst still meeting the corrosion rates.

The chemicals selected were known to have lower corrosivity – one a polymer which had been used successfully with F22 alloy, plus another polymer widely used in the North Sea where low corrosivity generally is required along with good environmental properties. This blend was successful in meeting the scale inhibition performance target and was found to offer good compatibility with F22 alloy under application conditions. Furthermore, both chemicals were suitable to meet Angolan decree on environmental acceptability.

The paper describes in detail the development test work carried out for corrosion assessment, inhibitor performance, formulation stability, brine compatibility to select this formulation and highlight the importance of synergistic blends for meeting particularly challenging scaling environments.

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