New Horizon for Downhole Scale Management Towards Sustained Well Production

Abstract

AbstractIron sulfide scales is considered one of the most commonly encountered formation scale in the oil and gas industry which can adversely impact well deliverability and integrity. Traditional chemical treatments using inorganic acids such as HCl are not favorable due to its corrosive nature and rapid generation of H2S gas. The success rate for such operation is further challenged by the molar ratio of iron to sulfur and the existing polymorph of iron sulfide such as pyrite, pyrrhotite, troilite, marcasite and mackinawite.This paper aims to share the laboratory development and field application results for a revolutionary chemistry that was developed as an integrated solution to dissolute iron sulfide scales and inhibit further scale nucleation. Extensive laboratory testing was conducted under anaerobic conditions to create an evolved chelating agent with high iron sulfide dissolution, minimal corrosion rate and no H2S generation. The experimental setup included in-situ mixing of Fe(+2) and S(-2) to create iron sulfide scale that were placed in glass vial reactors and exposed to specific temperature and pressure. Furthermore, a thorough evaluation of sulfide scale properties and behavior under varying reservoir pressure and temperature is incorporated into a computational model to understand and accurately control the scale deposition process.Several cleanout jobs have been successfully performed in the field using this treatment. Lab results showed minimal presence for the ferrous ion and total sulfide once filtered from the aqueous phase. Furthermore, the results for iron sulfide dissolution at different pH levels will be shared to determine the optimum pH values for the chelating agents. The collected data showed that this dissolver was able to outperform THPS based dissolvers without the adverse effects of HCl. Post job results will be discussed in this paper including job design, field execution, lessons learned and solid compositional analysis. Furthermore, inhibition program has been implemented based on the acquired results from this model and frequent inspection conducted showed no scale deposition over extended production periods.The novelty of this approach is its ability to efficiently remove iron sulfide scales and inhibit nucleation at early stages without relying on inorganic acids. Lab results will be discussed in detail to examine the role of chelating agents in iron sulfide dissolution at different pH levels under anaerobic conditions. Field deployment data will be shared to definitively prove the effectiveness of this treatment in removing and preventing further iron sulfide precipitation. This study will help shed some light on an issue that has long concerned the oil & gas industry and up to this date no effective prevention mechanism has been discovered.