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Iron sulphide (FeS), zinc sulphide (ZnS) and lead sulphide (PbS) are considered to be among the most challenging scales in terms of inhibition and removal. They can form by direct reaction of aqueous sulphide species with dissolved Fe, Zn and/or Pb and by the exchange between aqueous sulphide species with preformed iron compounds, such as iron oxide hydroxide. These existing iron compounds may have formed during production and/or intervention, such as an acid treatment. Similarly, PbS and ZnS can form by extracting sulphide from a more soluble sulphide scale i.e. Zn exchanging with Fe in FeS. The objective of this work was to investigate FeS formation and inhibition under a range of conditions including pH, temperature, salinity and proposed mode of formation. In addition, the interaction between iron, zinc and lead within solutions containing sulphide species was investigated The majority of this study was conducted under anaerobic conditions, with the scale formation and/or inhibition experiments being monitored by inductively coupled plasma (ICP) analysis, pH and particle size measurements. Among the tested scale inhibitors, two showed high efficiency against iron sulphide, however high pH and salinity had a detrimental impact on the performance of one of these products. Interestingly, these scale inhibitors prevented iron sulphide deposition even under aerobic conditions i.e. iron hydroxide partially preformed. Moreover, at sufficiently high concentrations of scale inhibitor, the deposition of zinc sulphide and lead sulphide was prevented even when these scales were formed via cation displacement i.e. zinc and lead displaced sulphide ions from pre-formed iron sulphide. The route of formation for FeS, ZnS and PbS was seen to have a significant impact on the inhibition process. The particle sizes of inhibited (suspended) FeS were significantly lower than the blank FeS samples, with this effect increasing with increased scale inhibitor concentration. This difference in particle size may have an important influence on in-line filter blocking tests and produced water quality issues.
Iron sulphide (FeS), zinc sulphide (ZnS) and lead sulphide (PbS) are considered to be among the most challenging scales in terms of inhibition and removal. They can form by direct reaction of aqueous sulphide species with dissolved Fe, Zn and/or Pb and by the exchange between aqueous sulphide species with preformed iron compounds, such as iron oxide hydroxide. These existing iron compounds may have formed during production and/or intervention, such as an acid treatment. Similarly, PbS and ZnS can form by extracting sulphide from a more soluble sulphide scale i.e. Zn exchanging with Fe in FeS. The objective of this work was to investigate FeS formation and inhibition under a range of conditions including pH, temperature, salinity and proposed mode of formation. In addition, the interaction between iron, zinc and lead within solutions containing sulphide species was investigated The majority of this study was conducted under anaerobic conditions, with the scale formation and/or inhibition experiments being monitored by inductively coupled plasma (ICP) analysis, pH and particle size measurements. Among the tested scale inhibitors, two showed high efficiency against iron sulphide, however high pH and salinity had a detrimental impact on the performance of one of these products. Interestingly, these scale inhibitors prevented iron sulphide deposition even under aerobic conditions i.e. iron hydroxide partially preformed. Moreover, at sufficiently high concentrations of scale inhibitor, the deposition of zinc sulphide and lead sulphide was prevented even when these scales were formed via cation displacement i.e. zinc and lead displaced sulphide ions from pre-formed iron sulphide. The route of formation for FeS, ZnS and PbS was seen to have a significant impact on the inhibition process. The particle sizes of inhibited (suspended) FeS were significantly lower than the blank FeS samples, with this effect increasing with increased scale inhibitor concentration. This difference in particle size may have an important influence on in-line filter blocking tests and produced water quality issues.
Summary Iron sulfide (FeS), zinc sulfide (ZnS), and lead sulfide (PbS) are considered to be among the most challenging scales in terms of inhibition and removal. They can form by the direct reaction of aqueous sulfide species with dissolved Fe, Zn, and/or Pb and by the exchange between aqueous sulfide species with preformed Fe compounds, such as Fe oxide hydroxide. These existing Fe compounds might have formed during production or intervention, such as an acid treatment. Similarly, PbS and ZnS can form by extracting sulfide from a more soluble sulfide scale (i.e., Zn exchanging with Fe in FeS). The objective of this work was to investigate FeS formation and inhibition under a range of conditions, including pH, temperature, and salinity, and to propose a mode of formation. In addition, the interaction between Fe, Zn, and Pb within solutions containing sulfide species was investigated. The majority of this study was conducted under anaerobic conditions, with the scale-formation/inhibition experiments being monitored by inductively coupled plasma (ICP) analysis and pH and particle-size measurements. Among the tested scale inhibitors (SIs), two showed high efficiency against FeS, but high pH and salinity had detrimental effects on the performance of one of these products. Interestingly, these SIs prevented FeS deposition even under aerobic conditions (i.e., Fe hydroxide partially preformed). Moreover, at sufficiently high concentrations of SI, the deposition of ZnS and PbS was prevented even when these scales were formed by means of cation displacement (i.e., displaced ZnS and PbS ions from preformed FeS). The route of formation for FeS, ZnS, and PbS was seen to have a significant effect on the inhibition process. The particle sizes of inhibited (suspended) FeS were significantly lower than those of the blank FeS samples, with this effect increasing with increased SI concentration. This difference in particle size might have an important influence on in-line filter-blocking tests and produced-water quality issues.
Iron sulfide (FeS) and zinc sulfide (ZnS) scales have been observed in many sour oil and gas wells. FeS often forms alongside other scales such as calcium carbonate and barium sulfate and such scales can be removed using chemicals like hydrochloric acid (HCl) and chelating agents. However, there are several drawbacks associated with the FeS removal by acid. For example, HCl acid, which outperforms other dissolvers has a high corrosion rate and generates hydrogen sulfide (H2S) gas as a byproduct. Other dissolvers, including chelating agents, often have low dissolution rates. Therefore, FeS inhibition is preferred as a strategy rather than allowing it to form followed by its removal. The objective of this paper is to investigate the inhibition efficiency of various inhibitors for preventing FeS and ZnS deposition. Different scale inhibitor (SI) chemistries have been examined over a wide range of parameters, including temperature, salinity, pH and concentrations of Fe, Zn and sulfide. Static formation and inhibition experiments were conducted and the progress of the reaction was monitored by inductively coupled plasma (ICP) analysis and pH. In addition, the inhibitor consumption in sulfide scale solutions has also been investigated; i.e. the inhibitor concentration has been monitored during the sulfide inhibition process to determine the role and fate of the SI itself. Polymeric scale inhibitors, including phosphino polycarboxylic acid (PPCA), showed a high inhibition efficiency for ZnS in different salinity and temperature conditions. On the other hand, some polymeric scale inhibitor that prevented the deposition of ZnS completely failed to inhibit FeS. It was found that, in mixed FeS and ZnS systems where both sulfide scales deposited, the precipitation of FeS had a negative impact on the inhibition efficiency for ZnS. By analogy, the FeS formation can affect the inhibition efficiency for other scales such as calcium carbonate and barium sulfate. In addition, in our SI consumption experiments we found that the scale inhibitor was consumed in ZnS solutions while there was no decrease (no SI consumption) in the scale inhibitor concentrations in FeS solutions. Based on these results, we demonstrate that it is easier to inhibit ZnS rather than FeS under the same conditions. The presence of FeS had a negative impact on the performance of the scale inhibitor for ZnS and similar effects might occur in FeS/conventional scale systems. For the first time in a sulfide scaling system, this work examines if the scale inhibitor remains at its original dosage in solution or if it declines. There were two distinct behaviors, the scale inhibitor was consumed in ZnS but not in FeS solutions.
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