Exploring Modified Alendronic Acid as a New Inhibitor for Calcium-Based Oilfield Scales

Organophosphorus compounds are well known as oilfield scale inhibitors. Earlier work showed that a series of new and well-known bone-targeting drugs incorporating non-toxic bisphosphonates (BPs) (PO3H2–C–PO3H2) gave good scale inhibition performance against calcite scale based on produced water from the Heidrun oilfield, Norwegian Sea, Norway. However, these chemicals showed only moderate calcium compatibility activity. In this project, we attempted to improve the inhibition performance and calcium tolerance of non-toxic BPs by introducing various functional groups (phosphonate (SI-2), sulfonates (SI-3 and SI-5), and carboxylates (SI-4, SI-6, and SI-7)) in the inhibitor structure backbone. All modified alendronic acid derivatives were screened for calcite and gypsum scale inhibition according to the NACE Standard TM0374-2007 protocol. We also report the calcite scale inhibition performance of all synthesized SIs according to the Heidrun oilfield, Norwegian Sea, Norway. In addition, the calcium tolerance and thermal stability activities of all synthesized SIs are reported. The tolerance results showed that all SIs gave better calcium compatibility than BPs reported earlier, with SI-5 giving the best results at high calcium concentrations (10,000 ppm). The corresponding attachment of an iminodi methylene/ethylene sulfonic moiety (i.e., SI-3 and SI-5) showed worse performance against gypsum scaling, whereas the methylenephosphonate derivative (SI-2) and the carboxylated derivatives (SI-4, SI-6, and SI-7) showed improved performance. For calcite scaling, the NACE standard test gave significantly lower inhibition results than the Heidrun-based produced water due to the former having a higher calcium concentration and calcite supersaturation. It was also found that SI-2, SI-5, and SI-7 showed good thermal stability at 130 °C for 1 week.