Evaluation and application of calcite scale inhibitor in an offshore pH stabilised MEG system—an Australian first

Abstract

Calcite scale mitigation in pH stabilised MEG systems is a growing concern for the industry as a number of systems are planned for upcoming Australian gas projects. Issues are insignificant at first gas when water of condensation is present. When formation water production occurs, scale management becomes a critical component of project feasibility. A closed loop pH stabilised MEG regeneration system located in the Otway Basin faced these challenges. Severe calcite scaling in a subsea well, which led to choke failure and MEG system fouling, was successfully controlled by the application of a specific polymeric scale inhibitor. The operating nature of a pH stabilised closed loop MEG system eliminates conventional scale inhibitor chemistries. Customised polymer chemistries were selected for review predominately due to their ability to persist in a variety of harsh conditions, including the MEG regeneration process. Technical qualification to validate scale inhibitor functionality was completed using protracted compatibility testing and Dynamic Scale Loop assessment. Evaluation of inhibitor performance and behaviour was accomplished using customised monitoring processes focusing on scale inhibitor detection, identifying measurement interferences, and interaction with precipitated solids. Field implementation provided excellent results with the inhibitor averting further severe scaling issues, resulting in minimal production system disruption. Fouling of the MEG regeneration system in particular has been minimised, resulting in a reduced frequency and length of cleaning cycles. This peer-reviewed paper will detail the evaluation, application and monitoring fundamentals when introducing scale inhibitors into pH stabilised MEG systems.