The development of combination products for scale and corrosion inhibition for fields producing at high downhole temperatures (~150C) and that generate produced waters with high Calcium concentrations can be a challenging undertaking. Traditional phosphonate scale inhibitors can be very effective; however they have been shown to form insoluble inorganic scales at high calcium concentrations that can plug and fail capillary strings. The development in this work considered the use of polymeric type scale inhibitor and a newly recently introduced high temperature corrosion inhibitor. Again because this is a high temperature application the evaluation of the corrosion performance can also be challenging due to the difficulties derived from attempting to prevent the scaling process while trying to obtain meaningful corrosion performance data. The developed combination product was stable at 150C compatible with capillary string materials and outperformed an incumbent product based on a phosphonate scale inhibitor and a more traditional type of corrosion inhibitor.

As the oil industry continues to operate in more complex and ultrahigh temperature environments scale control becomes an ever increasing challenge. Scale inhibitors are being pushed to their operational limits and start to lose their efficiency against both calcium carbonate and calcium sulphate scales at >200°C. It is therefore essential to develop the next generation scale inhibitor to work effectively in harsh high temperature environments such as steam floods and geothermal wells.In this study details will be provided of the thermal stability of a novel biodegradable phosphonate scale inhibitor at temperatures up to 250°C. In addition examples of calcium sulphate and calcium carbonate scale control will be provided at 200°C and 250°C respectively where the inhibition performance of the novel phosphonate has provided significant improvements compared to other phosphonates and polymeric scale inhibitors known to be stable at high temperature.The work for calcium sulphate has focussed on steam flood applications where downhole temperatures reach ~200°C and the scale inhibition performance was tested using dynamic scale loop tests based upon a known industry standard procedure. Calcium carbonate inhibition was also tested at 200°C using a similar procedure and in addition with a geothermal brine at 250°C.  The new phosphonate scale inhibitor has also been designed to be biodegradable and can be deployed by both continuous injection and scale squeeze treatment. Careful consideration was also given in the molecular design process for high calcium tolerance and details of brine compatibility at high temperature will be provided.This paper presents details of the development of a biodegradable thermally stable and calcium tolerant phosphonate scale inhibitor for both calcium sulphate and calcium carbonate scale control in ultrahigh temperature environments at ≥200°C. In addition the environmental test data will be discussed along with a field example of deployment of the new phosphonate scale inhibitor for calcium carbonate scale control in a high calcium brine (30000mg/l) in West Africa.