Unravelling the Processes of the H2S Generation in the North-western Pyrenees (France)
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Scale formation is mostly governed by scaling ion concentrations and fluid conditions (pressure, temperature, and pH). Sulfide scale formation is most commonly initiated through the mixing fluids containing scaling cations (Fe2+, Zn2+ and Pb2+) or sulfidic anions (H2S(aq), HS- and S2-), or, more rarely, in a single fluid containing both ions which is undergoing physical condition changes, such as a pressure drop or pH change. The literature has extensive reviews of sulfide scales formed by mixing two fluids in both static and dynamic tests. The self-scaling of metal sulfides in a single fluid, however, has been less investigated. An experimental setup and procedure have been developed to investigate the impact of various factors, such as pH (0 - 10), sulphide and metal ion concentrations and salinity (3.5 - 20 wt. %), on the formation of sulfide scales in general and iron sulfide (FeS) in particular. This new setup provides anaerobic conditions to isolate and prevent the interference of atmospheric oxygen, while retaining aqueous and gaseous sulfide in solution. The setup is comprised of airtight vials and Hungate-type tubes equipped with septum-caps to facilitate the gas-tight liquid transfers required in such experiments. The concentrations of sulfide ranged from 100 to 1,000 mg/L, and iron, zinc and lead were studied at levels in the range of 50 - 100 mg/L. The formation of sulfide scales was measured by monitoring the depletion of cation concentration in aqueous solution at various pH values. The excess amount of sulfide concentration significantly affected the formed iron sulfide by affecting the pH at which initial cation depletion occurred. The higher sulfide excesses gave an FeS precipitation onset at lower pH levels, and larger FeS particle size than lower levels of sulfide excess. These findings directly affect the scale inhibition design, as most sulfide scale control chemicals are dispersants. Therefore, particle size is very relevant to these dispersants in terms of the inhibitor loading and efficiency. The assumption that sulfide scale is principally reliant on the cation concentration, particularly if limiting, is inaccurate, and sulfide excess must also be quantified and taken into consideration in the inhibition design.
Scale formation is mostly governed by scaling ion concentrations and fluid conditions (pressure, temperature, and pH). Sulfide scale formation is most commonly initiated through the mixing fluids containing scaling cations (Fe2+, Zn2+ and Pb2+) or sulfidic anions (H2S(aq), HS- and S2-), or, more rarely, in a single fluid containing both ions which is undergoing physical condition changes, such as a pressure drop or pH change. The literature has extensive reviews of sulfide scales formed by mixing two fluids in both static and dynamic tests. The self-scaling of metal sulfides in a single fluid, however, has been less investigated. An experimental setup and procedure have been developed to investigate the impact of various factors, such as pH (0 - 10), sulphide and metal ion concentrations and salinity (3.5 - 20 wt. %), on the formation of sulfide scales in general and iron sulfide (FeS) in particular. This new setup provides anaerobic conditions to isolate and prevent the interference of atmospheric oxygen, while retaining aqueous and gaseous sulfide in solution. The setup is comprised of airtight vials and Hungate-type tubes equipped with septum-caps to facilitate the gas-tight liquid transfers required in such experiments. The concentrations of sulfide ranged from 100 to 1,000 mg/L, and iron, zinc and lead were studied at levels in the range of 50 - 100 mg/L. The formation of sulfide scales was measured by monitoring the depletion of cation concentration in aqueous solution at various pH values. The excess amount of sulfide concentration significantly affected the formed iron sulfide by affecting the pH at which initial cation depletion occurred. The higher sulfide excesses gave an FeS precipitation onset at lower pH levels, and larger FeS particle size than lower levels of sulfide excess. These findings directly affect the scale inhibition design, as most sulfide scale control chemicals are dispersants. Therefore, particle size is very relevant to these dispersants in terms of the inhibitor loading and efficiency. The assumption that sulfide scale is principally reliant on the cation concentration, particularly if limiting, is inaccurate, and sulfide excess must also be quantified and taken into consideration in the inhibition design.
Numerous well operations, including water injection, varying stimulation approaches, and enhanced oil recovery (EOR) techniques are implemented during the production period in order to maintain the longevity of hydrocarbon production. However, reservoir formation, production, and injection facilities are often impacted by these treatments. Well operations induce inorganic scale to form near-wellbore regions and in various production and injection structures. Consequently, the deposition of scales hinders assessing an optimum hydrocarbon production as their precipitation on formation, various surface, and downhole equipment leads to many problems, including pressure decrement, formation damage, and operational failure of subsurface equipment. As a control measure to prevent scale precipitation downhole squeeze treatment is commonly used in the petroleum industry. By applying a squeeze treatment, a scale inhibitor solution is introduced into a formation above the formation pressure, allowing the scale inhibitor to get into the deep into near-wellbore formation. Downhole squeezing allows scale inhibitors to adsorb on the internal rock surface to avoid the settling down of scale precipitates. Thus, the study of adsorption of different types of inhibitors, such as chelating agents, polymeric inhibitors, and polyphosphates on formation is becoming necessary. The study incorporated several experimental techniques, including dynamic adsorption experiments using coreflooding setup, ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry), and ζ-potential measurements targeting evaluation of adsorption of aminopolycarboxylic acids in carbonate rocks and iron precipitation in calcite mineral. Potential precipitation of iron in varying pH environments and causing the formation of iron-containing scales was assessed through ζ-potential measurements. The findings reveal that the concentration of aminopolycarboxylic acids plays a significant role in their adsorption on carbonate rocks. The adsorption is also affected by different factors, such as the presence of salts. The results of ζ-potential measurements showed that iron (II) and iron (III) precipitation is controlled by the pH environment in calcite minerals. The treatments with 20 wt% ethylenediaminetetraacetic acid (EDTA) and diethylenetriamine pentaacetate acid (DTPA) produced the highest adsorption capacity in carbonate rock samples by inhibiting 84% and 85% of iron (III) ions, respectively. The encountered permeability damage in the adsorption tests was between 25% and 32%. Moreover, the presence of the salts considerably decreased the adsorption of EDTA and caused almost 20% more permeability reduction. Unlike the conventional testing methods for inhibitor adsorption, a novel experimental setup, coreflooding was used during the inhibitor adsorption, and scale inhibition in carbonate formation.
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