Mechanisms of Environmentally Acceptable Inhibitors for Zinc Sulphide Inhibition

Williams, Helen; Tortolano, Christopher; Champion, Nalco; Adenuga, T

doi:10.2118/173771-ms

Cited by 5 publications

References 19 publications

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A Systematic Investigation of Factors Affecting the Formation of Zinc Sulfide ZnS

et al. 2016

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Work was undertaken to systematically investigate the factors that affect the formation of zinc sulfide in an aqueous system. Experiments were performed at a series of temperatures from room temperature up to 90 °C, at a range of initial pH values and in two brines systems. The effect of pH was further examined by changing the salt from Na2S.9H2O to NaSH.xH2O, therefore changing the initial sulfide source from S2- to HS-, as part of an ongoing method development strategy. A variation of the standard barium sulfate static bottle test was used, in which the two bottles to be mixed contained aqueous "H2S" and zinc, respectively. Having pH adjusted the zinc brine to values calculated by the FAST sulfide model, the brines were pre-heated to the required temperature and mixed. Aliquots were removed at 2, 4 and 24 hours to perform elemental analysis by ICP and pH measurements were performed on all samples once they had returned to room temperature. In addition, particle size analysis and ESEM examination of the resulting precipitate were also performed for a subset of the samples prepared. The reaction between zinc and aqueous "H2S" was quantitative at all temperatures up to 90 °C and in both brines. The final pH values of the supernatant were independent of the zinc brine pH and instead were dependent on the molar ratio of zinc and sulfide ions. A high pH, sulfide dominated, and a low pH, zinc dominated, plateau region were seen with a sharp inflection between the two. As a consequence, reaching field representative pH values was seen to be extremely difficult while retaining the ability to alter the relative concentrations of the reacting ions. Altering the sulfide source yielded the same trend, albeit with different absolute values. These observations have been rationalised with reference to the thermodynamic constants governing the reaction through scale prediction modelling. The work presented here provides a greater understanding of the factors governing the formation of zinc sulfide scale and the considerations required for more industrially relevant formation and inhibition experiments in the future.

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A Systematic Investigation of Factors Affecting the Formation of Zinc Sulfide ZnS

et al. 2016

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A Systematic Investigation of Factors Affecting the Formation of Zinc Sulfide (ZnS)

Graham¹,

Singleton²,

Sorbie³

et al. 2017

SPE Production &Amp; Operations

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Summary Work was undertaken to systematically investigate the factors that affect the formation of zinc sulfide (ZnS) in an aqueous system. Experiments were performed at a series of temperatures from room temperature up to 90°C, at a range of initial pH values and in two brine systems. The effect of pH was examined further by changing the salt from Na2S·9H2O to NaSH·xH2O, therefore changing the initial sulfide source from S2– to HS–, as part of an ongoing method-development strategy. The formation of ZnS was achieved by the equivolume mixing of two preheated bottles, which contained aqueous “H2S” and zinc ions, respectively. Having pH adjusted the zinc brine to values calculated by an in-house thermodynamic model, the brines were preheated to the required temperature and mixed. Aliquots were removed at 2, 4, and 24 hours to perform elemental analysis by inductively coupled plasma optical emission spectrometry (ICP-OES), and pH measurements were performed on all samples after they had returned to room temperature. In addition, particle-size analysis and environmental scanning electron microscopy (ESEM) examination of the resulting precipitate were also performed for a subset of the samples prepared. The reaction between zinc ions and aqueous “H2S” was quantitative at all temperatures up to 90°C and in both brines. The final pH values of the supernatant were independent of the zinc brine pH, and instead were dependent on the molar ratio of zinc and sulfide ions. With a high pH, sulfide-dominated, and a low pH, zinc-dominated, plateau regions were seen with a sharp inflection between the two. As a consequence, reaching field-representative pH values was seen to be extremely difficult while retaining the ability to alter the relative concentrations of the reacting ions. Altering the sulfide source yielded the same trend, although with different absolute values. These observations have been rationalized with reference to the thermodynamic constants governing the reaction through scale-prediction modeling. The work presented here provides a greater understanding of the factors governing the formation of ZnS scale and the considerations required for more industrially relevant formation and inhibition experiments in the future.

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Laboratory Investigation of Zinc and Lead Sulphide Inhibition

Alharbi¹,

Graham²,

Sorbie³

2018

SPE International Conference and Exhibition on Formation Damage Control

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The formation of zinc sulphide (ZnS) and/or lead sulphide (PbS) has been a persistent problem, particularly in high temperature high pressure HT/HP fields. ZnS and PbS deposition can pose safety hazards and have serious economic consequences including reduction in well productivity and may require the implementation of an effective scale mitigation and removal strategy. HT/HP fields are prone to critical changes in temperature and pressure and, in addition, they usually have high salinity brines; indeed they are often referred to as HP/HT/HS systems. When these factors (pressue/temperature/salinity) vary together, they tend to trigger the formation of inorganic scales including sulphides. Apart from the role of temperature and salinity in scale formation, these (HT/HS) conditions often negatively impact scale inhibitor performance due to chemical degradation or incompatibility. The objective of this study was to investigate ZnS and PbS formation (as single or combined scales) and inhibition over a range of parameters including pH, temperature, salinity, time and initial Zn, Pb and H2S concentrations. Polymeric and phosphonate scale inhibitors (SIs) were tested using static scale formation experiments, with samples being analysed by inductively coupled plasma (ICP) analysis, Environmental Scanning Electron Microscopy (ESEM), pH and particle size distribution measurements. Of the seven scale inhibitors tested, only two demonstrated inhibitory capacity at active concentrations of 100 ppm or below. SI-2, a high-molecular weight polymer, was remarkably effective in preventing both zinc and lead sulphide deposition regardless of the final supernatant pH. SI-3 showed more limited efficacy compared with SI-2 with its highest inhibition being achieved at low pH values.This information is important to consider when designing scale inhibitor treatments; as carbon dioxide liberates from produced water due to decreasing pressureit causes the pH to increase, which may cause a drop in the inhibition efficiency of some scale inhibitors. Increasing the brine salinity had a detrimental impact on the performance of the tested scale inhibitors. Neither SI-2 nor SI-3 were able to prevent PbS deposition by ionic displacement of Zn from ZnS by Pb2+ despite the fact that both scale inhibitors were effective against PbS under the same conditions using the conventional scale inhibition experiments. The particle size distribution of the partially inhibited ZnS and PbS particulates was found to be dependent on the type and concentration of the scale inhibitor, the final pH and salinity. The difference in particle size could have significant effects on in-line filter blocking tests and produced water quality issues.

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Mechanisms of Environmentally Acceptable Inhibitors for Zinc Sulphide Inhibition

Cited by 5 publications

References 19 publications

A Systematic Investigation of Factors Affecting the Formation of Zinc Sulfide ZnS

A Systematic Investigation of Factors Affecting the Formation of Zinc Sulfide ZnS

A Systematic Investigation of Factors Affecting the Formation of Zinc Sulfide (ZnS)

Laboratory Investigation of Zinc and Lead Sulphide Inhibition

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