Iron sulfide deposition is a ubiquitous phenomenon in sour oil and gas wells and presents unique challenges for its control and management downhole. The majority of current FeS anti-scale chemical technologies tend to be ‘reactive’ rather than ‘proactive’ for downhole scale mitigation, and currently there are few FeS scale inhibitor squeeze options available. The following paper details work performed to modify an existing novel and unique sulfide scale inhibitor to further enhance its sulfide scale inhibition efficacy and to reconfigure the polymer molecule structure for improved adsorption / desorption behavior sufficient to allow squeeze application for control and mitigation of FeS scale downhole.
All new polymeric inhibitor chemistries were tailored for high total dissolved solid (TDS) and high downhole temperature chalk sour gas well application. Further ranking was performed via automated static adsorption tests, iron sulfide efficacy tests and high calcium brine compatibility jar tests to identify the best squeeze applicable candidates for final formation damage coreflood testing.
Introduction of new anchor group functionality into the polymer resulted in improved adsorption behavior (identified via the static adsorption test), while having minimal impact on the inhibitors high TDS / high calcium brine tolerance and also on its FeS scale inhibition performance. The kinetic adsorption study showed > 2 mg inhibitor/g rock adsorption on field analogous chalk rock, which is markedly higher compared to the original parent sulfide inhibitor molecule or other new polymeric variants synthesized without the new anchor groups. FeS scale inhibitor adsorption was further improved by optimizing the ratio of monomer and functional groups on the polymer. Simulated field squeeze coreflood testing revealed no appreciable formation damage to outcrop core analogue under simulated field application conditions and the new variant inhibitor chemicals also showed significant useful adsorption/desorption behaviour.
The new polymeric scale inhibitors are suitable for both continuous injection and squeeze application for control of FeS scale in high temperature and high calcium ion sour gas chalk wells. For squeeze application, testing revealed a low formation damage potential combined with significant chemical retention for potentially extended squeeze lifetime in the field. Ultimately this technology heralds a new era in downhole scale management for sour producer wells plagued by FeS scale via reduction of treatment frequency for assured well integrity.