A Novel Phosphonate Scale Inhibitor for Scale Control in Ultra High Temperature Environments

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 >400°F. It is therefore essential to develop the next generation scale inhibitor to work effectively against scale in harsh, high temperature environments such as steam floods and gas wells. In this study, details will be provided on the thermal stability test of a novel, biodegradable phosphonate scale inhibitor at temperatures 300°F and 400°F at two pH values, pH 4.0 and pH 6.0. Bottle tests on calcium carbonate and calcium sulfate were conducted with the thermal-aged phosphonate for their inhibition. Dynamic tube blocking tests were also conducted for calcium carbonate and calcium sulfate inhibition at 392°F to demonstrate the performance of the inhibitor. The new phosphonate scale inhibitor has also been designed to be biodegradable and it can be deployed by both continuous injection and scale squeeze treatment which is an advantage compared to polymers as they are often less suitable for high temperature scale squeeze treatments. 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 evaluation 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 ~400°F. In addition, the environmental test data will be discussed along with details of a field example of continuous downhole deployment of the new phosphonate scale inhibitor for calcium carbonate scale control in a high calcium brine (30,000 mg/L).