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 H2Sn (n = 2-9), are fundamental to understanding sulfur chemistry in natural gas reservoirs. Despite their importance, the abiogenic origins and reaction pathways of H2Sn 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 H2Sn. 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 H2Sn under varying reservoir conditions, offering insights into their decomposition tendencies and subsequent formation of H2S and elemental sulfur (S8).