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Abstract <p>Thermochemical sulfate reduction (TSR) is one of the processes that are responsible for the generation of hydrogen sulfide in a reservoir. Recently, new hydrogeochemical modeling approaches have been developed to investigate TSR in hydrocarbon reservoirs. These models were developed to understand the basic hydrogeochemical mechanisms for H<sub>2</sub>S production, as well as the factors that control this process. In this paper, we have modeled the TSR process in Permian–Lower Triassic deposits using the Shanul gas field in southwestern Iran as an example. The one-dimensional diffusive mass transport model (PHREEQC) we used is based on equilibrium reactions for gas—water–rock interactions and kinetic reactions for sulfate reduction and methanogenesis. The simulation results indicate that the intensity of the TSR reaction and the volume of driven H<sub>2</sub>S (hydrogen sulfide) are significantly influenced by three factors: the mineral composition of the host reservoir rock, the pressure drop in the reservoir, and the pH of the formation water. The results show that the mineral composition of the host rocks affects the intensity of the TSR process. The presence of iron-containing minerals can significantly inhibit the production of H<sub>2</sub>S. The modeling results suggest that the presence of a 5% level of iron-containing minerals has the potential to completely remove hydrogen sulfide from a system within 20 years. Additionally, it has been observed that changes in reservoir pressure after production or injection significantly affect the concentration of hydrogen sulfide within the reservoir. A drop in pressure up to 50% (from 600 to 300 atm) of the initial reservoir pressure increases the H<sub>2</sub>S concentration by more than ten times (from 4 × 10<sup>–4</sup> to 4 × 10<sup>–3</sup> mol/kg (H<sub>2</sub>O). In addition, it has been shown that changing the pH of an aqueous solution can significantly change the rate of the TSR. According to the simulation results, a 20% decrease in the pH of water (from 6.5 to 5.7) would lead to an increase in H<sub>2</sub>S concentration from 8 × 10<sup>–4</sup> to 16 × 10<sup>–4</sup> mol/kg (H<sub>2</sub>O).</p>

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Hydrogeochemical Modeling of Hydrogen Sulfide Formation in a Carbonate Reservoir: A Case Study of the Shanul Field, Southwest Iran

  • 期刊论文

  • 发表日期：

    2025年2月1日

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  • H. Gholizadeh,
  • E. A. Krasnova,
  • A. V. Korzun,
  • A. R. Rabbani

摘要

Abstract

Thermochemical sulfate reduction (TSR) is one of the processes that are responsible for the generation of hydrogen sulfide in a reservoir. Recently, new hydrogeochemical modeling approaches have been developed to investigate TSR in hydrocarbon reservoirs. These models were developed to understand the basic hydrogeochemical mechanisms for H2S production, as well as the factors that control this process. In this paper, we have modeled the TSR process in Permian–Lower Triassic deposits using the Shanul gas field in southwestern Iran as an example. The one-dimensional diffusive mass transport model (PHREEQC) we used is based on equilibrium reactions for gas—water–rock interactions and kinetic reactions for sulfate reduction and methanogenesis. The simulation results indicate that the intensity of the TSR reaction and the volume of driven H2S (hydrogen sulfide) are significantly influenced by three factors: the mineral composition of the host reservoir rock, the pressure drop in the reservoir, and the pH of the formation water. The results show that the mineral composition of the host rocks affects the intensity of the TSR process. The presence of iron-containing minerals can significantly inhibit the production of H2S. The modeling results suggest that the presence of a 5% level of iron-containing minerals has the potential to completely remove hydrogen sulfide from a system within 20 years. Additionally, it has been observed that changes in reservoir pressure after production or injection significantly affect the concentration of hydrogen sulfide within the reservoir. A drop in pressure up to 50% (from 600 to 300 atm) of the initial reservoir pressure increases the H2S concentration by more than ten times (from 4 × 10–4 to 4 × 10–3 mol/kg (H2O). In addition, it has been shown that changing the pH of an aqueous solution can significantly change the rate of the TSR. According to the simulation results, a 20% decrease in the pH of water (from 6.5 to 5.7) would lead to an increase in H2S concentration from 8 × 10–4 to 16 × 10–4 mol/kg (H2O).