Molecular mechanism of elemental sulfur dissolution in H 2 S under stratal conditions.

Resulting from the solubility reduction of elemental sulfur during the development of high sulfur gas formations, sulfur deposition often occurs to reduce the gas production and threaten the safety of gas wells. Understanding the dissolution mechanism of elemental sulfur in natural gas is essential to reduce the risk caused by sulfur deposition. Because of the harsh conditions in the high-sulfur formations, it remains challenging to in situ characterize the dissolution-precipitation processes, making deficient the knowledge of sulfur dissolution mechanism. The dissolution of sulfur allotropes (S N , N = 2, 4, 6 and 8) in H 2 S, the main solvent of sulfur in natural gas, is studied in this work by means of first-principles calculations and molecular dynamics simulations. While S 6 and S 8 undergo physical interaction with H 2 S under the conditions corresponding to those at 1-6 km stratigraphic depths, S 2 and S 4 react with H 2 S and form stable polysulfides. Unravelling the mechanism would be helpful for understanding and controlling the sulfur deposition in high-sulfur gas development.