Development and Qualification of New Zinc and Lead Sulphide Scale Inhibitors for Application under Harsh Conditions

Abstract

Abstract The paper will describe the challenges facing sulphide scale control in the challenging environment found in Totals Elgin and Franklin Fields. It will present the advances made in developing new thermally stable and compatible chemical inhibitors able to withstand the extreme conditions in these fields. The paper will then describe the test methodologies and experimental approach developed to examine the performance of various prototypes or candidate chemicals followed by more detailed testing on selected chemicals under the more challenging field representative conditions as well as application specific testing for both squeeze treatment and downhole continuous injection at temperatures of 196°C/282 °F. In collaboration with University of Lyon Total has developed a range of new inhibitor types specifically designed to inhibit sulphide scales and remain stable under the harsh conditions of these fields. The chemicals have been qualified independently using recently developed test methodologies for lead and zinc sulphide and show better performance against these unconventional scales comparing to the other chemistries examined. In addition, a new method was developed for scale inhibitor residual analysis. This method based on time resolved fluoroscopy allows a quick and very sensitive measurement. The work concludes that a new range of Zn/Pb sulphide specific chemicals have been developed for field application with selected species also being suitable for application under the extreme conditions of the Elgin and Franklin Fields. Zinc and lead sulphide scales became an increasing challenge in oil and gas production. More specifically when formed from wells producing under very severe conditions of high temperature (196°C/282 °F) and high salinity formation waters such as those experienced in Central Graben Fields, their prevention by conventional scale inhibitors has proved challenging. To date after extensive chemical qualification over several years, no conventional scale inhibitor has been found which can both inhibit lead and zinc sulphide and survive under the extreme conditions of these fields. Therefore, the results in this paper represent a significant advance in the ability to control sulphide scales and test the inhibition under appropriate conditions.