The Application of Scale Inhibitors for Downhole Capillary Injection Under Ultra High Temperature

Abstract

Scale inhibitors have been widely used in oil and gas production as well as oil processing plants to control the formation of mineral scales. However, most scale inhibitors tend to lose efficiency as scaling temperatures above 400°F due to the thermal degradation of the chemicals. A customer in the Middle East reviewed their scale management strategy for a steam flood project with application temperatures up to 450°F and requested a suitable scale inhibitor for downhole capillary injection to prevent the formation of calcium carbonate and calcium sulphate scales. Several scale inhibitor products were selected for scaling inhibition tests based upon known high temperature stability. Dynamic tube-blocking test results indicated that three selective inhibitor products were able to mitigate the formation of calcium scales at 450°F effectively. These three products are fully compatible with the formation waters up to 10,000 ppm and were selected for further thermal stability and corrosion tests. Product A and B had good general corrosivity results, but product B was considered to fail the capillary approval test as there was extensive solid generation/phase separation observed after the thermal aging process at 450°F. Product C was also considered unsuitable as it showed aggressive corrosion rates. In conclusion, Product A is recommended for downhole capillary application in this steam flood project based upon the test results in this study and its previous successful downhole capillary application in the field at 400°F. Due to the high application temperature, special precautions may be necessary for preservation of the capillary string.