Formation pathways of hydrogen polysulfides in sulfur-bearing natural gas reservoirs from density functional theory calculations

Context

The interaction mechanisms between a sulfur atom (S) and hydrogen sulfide (H₂S), as well as the formation and stability of H₂S_n (n = 2–9), are fundamental to understanding sulfur chemistry in natural gas reservoirs. Despite their importance, the abiogenic origins and reaction pathways of H₂S_n in natural gas fields remain inadequately understood. Clarifying these mechanisms is essential for addressing sulfur deposition challenges, which have direct implications for extraction efficiency, operational safety, and reservoir management.

Methods

This study utilized quantum chemistry calculations to systematically investigate the reaction mechanisms between sulfur atoms and hydrogen sulfide, with a particular focus on the formation of H₂S_n. Transition state (TS) searches were conducted to identify energetically favorable reaction pathways, and intrinsic reaction coordinate (IRC) analyses were performed to validate the reaction trajectories. The kinetics and thermodynamics of H₂S₂ formation from elemental sulfur and H₂S were comprehensively evaluated. Additionally, stability analyses were carried out to assess the relative stability of H₂S_n under varying reservoir conditions, offering insights into their decomposition tendencies and subsequent formation of H₂S and elemental sulfur (S₈).