Metal sulfides such as iron sulfide (FeS), zinc sulfide (ZnS) and lead sulfide (PbS) scaling have been a persistent flow assurance problem in oil and gas production. FeS is ubiquitous in nature; however, ZnS and PbS are exotic scales but still pose significant scaling issues especially at HT wells. Efficient chemical treatment of those sulfides scales has not been found yet. Therefore, this study seeks to identify new chemical compound(s) to inhibit metal sulfide scale formation. A strictly anoxic static bottle test setup was designed and various chemical formulations were screened toward FeS, ZnS and PbS scale nucleation and growth inhibition. Thermal stability of the chemicals (150 °C for 18 hours) and phase transformation behavior of FeS scale with and without chemical treatment (75 °C for up to 10 days) were also conducted in glass container under anoxic environment. Aqueous phases as well as metal sulfide solid products were characterized using ICP-OES, X-ray diffraction, SEM, ATR-FTIR and other analytical techniques.

Our laboratory studies indicate that a polymeric compound containing amide or its derivative functionalities showed a promising effect by preventing metal sulfide scale deposition at threshold quantities. Specifically, the polymer did not inhibit the formation of the FeS, ZnS and PbS particles; however, it significantly influenced the growth and deposition behaviors by dispersing nano-particulates for an extended period of time. The thermal stability test results indicated that performance is not likely to be influenced at 150 °C even after 18 hours of ageing. Polymer treated and untreated FeS particulates were tested for heat induced phase transformation to pyrite and result indicated that polymer is highly efficient for inhibition of FeS phase transformation as well. Similarly, interference of performances towards metal sulfide dispersion due to the presence of other scaling materials (such as barite, iron oxides) and deposition tendency of dispersed metal sulfide particles onto flowlines were also tested and preliminary results look encouraging. Mechanistic aspect of polymer-particles interaction that prevents particle growth and deposition of FeS, ZnS and PbS scales are discussed. Despite its huge industrial and economic importance, an efficient solution of metal sulfide scale control is still an elusive goal. Based on our current laboratory results, it is believed that these polymers will provide a novel chemical treatment option for simultaneous control of these three sulfides (FeS, ZnS and PbS) scaling issues.

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