Accounting for 1.2 million bbls/day the Bakken shale plays a significant part in the North American unconventional boom. The formation is characterized with low porosity and permeability where wells exhibit high initial production rates and steep decline curves. Mitigating excessive decline is paramount to maintain return on investments.The system conditions and the produced water in the Bakken shale causes challenges that can impact productivity. The water composition is generally characterized with high total dissolved solids (TDS) resulting in high scaling tendencies for various species. In addition corrosion is also a challenge due to high TDS high downhole temperature (~250 °F) medium CO2 partial pressure (40-50 psi) and varying shear.A chemical qualification process is herein discussed where a combination corrosion- and scale inhibitor has been developed. The chemical is a synergistic blend of corrosion inhibitor actives and surfactants for corrosion mitigation and solids control combined with scale inhibitor and chelating agent for high iron tolerance scale control. The product had to be tailored to a chemical injection system that involves concurrent injection of several other production chemicals into a fresh water line that is subsequently injected downhole at elevated temperatures in a high TDS brine.Key words: Scale inhibitor corrosion inhibitor high TDS compatibility combination production chemical Bakken

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.