Investigation of the impact of ferrous species on the performance of common oilfield scale inhibitors for mineral scale control

Abstract Mineral scale deposition is a water-associated production threat for oil and gas productions. Scale deposition can lead to pipe throughput reduction and change in facility surface properties. Scale inhibitors are widely used in oilfield operations to control scale deposition. Fe(II) (ferrous) species is commonly encountered in oilfield produced waters and it is widely recognized that the presence of Fe(II) can impact the performance of scale inhibitors. However, the existing experimental results of Fe(II) impact on scale inhibitors are controversial, especially in barium sulfate system. This is partially due to the difference in dissolved oxygen level among different studies since a trace amount of dissolved oxygen can readily oxidize Fe(II) into Fe(III). In this study, a rigorously-maintained laser-based anoxic experimental setup was adopted to evaluate the impact of Fe(II) species on scale inhibitor performance in controlling barium sulfate scale. The anoxic setup utilized argon gas purging and reducing chemical addition and can maintain a dissolved oxygen level in μg L −1 (ppb) level. The experimental results suggest that at an anoxic condition, the presence of Fe(II) has a detrimental impact on the performance of scale inhibitors and such impact varies with different types of scale inhibitors. Solution pH and temperature can also affect the Fe(II) impact on scale inhibitors. In addition, two common oilfield chelating chemicals, i.e., EDTA and citrate, have been evaluated for their roles in reversing the detrimental impact of Fe(II) on scale inhibitors. It shows that at the experimental condition only citrate can effectively reverse the adverse impact of Fe(II) on scale inhibitor. This study provides the experimental approach and technical insights for evaluation of scale inhibitor performance in an anoxic condition.