The general perception in the oil and gas industry is that the presence of ferrous iron in produced water can have adverse effects to the performance of scale inhibitors in controlling the build-up of calcium carbonate (CaCO3) and barium sulfate (BaSO4) scales. However, the exact causes of its impact to scale inhibition are not clearly understood as previous studies appear to be influenced by the type of tests and the procedures adopted.
This paper presents some aspects of two case studies on the behavior of several iron tolerant scale inhibitor chemistries in water containing different levels of iron (II) ion. Laboratory assessments of the performance of the inhibitors were based on anaerobic static jar studies, Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Spectroscopy (EDXS) analysis and Dynamic Scale Loop (DSL) tests on both calcium carbonate and barium sulphate. Discussion is made to elucidate the mechanisms involved during scale inhibition when in the presence of different levels of iron (II) ion.
Mineral scale formation and deposition (e.g., CaCO3, BaSO4) can lead to unacceptable safety risks and the increase of operational costs 1-2. The build-up of scale deposit layers can compromise the performance, malfunctioning and/or operational safety of process equipment (e.g. heat exchangers, subsurface safety valves, pumps, tubing, etc.). Such failures can result in system downtime, reduced revenue, increased maintenance and operational costs. With the above reasons, the standard industrial practice adopted by many operators is to apply chemical solutions to ensure flow assurance, which are considered to be the most cost-effective approach and the preferred route to prevent and mitigate most of flow assurance and piping integrity problems 3-4.
An effective scale inhibitor plays a very important role in maintaining flow assurance integrity in oil and gas production systems. In recent years, oil and gas exploration and production are taking place in more arduous environment and remote locations, with which the industry has been faced with many new challenges, including unconventional resources, deeper formations, higher temperature, higher pressure, higher content of scale forming ions, protection of the environment and reduction in total cost of operation etc. Innovative techniques and solutions have been developed to address the operational issues. Appropriate chemical selections and applications form part of the elements in meeting these challenges4-5.
