Hydrolysis of Pyrite: a Possible Pathway for Generation of High Concentrations of H2S Gas in Deep-buried Reservoirs?

Abstract

Sulfates are conventionally regarded as the main sulfur source for H2S gas in sedimentary basins. In recent years, however, some theoretical insights and laboratory experiments indicate that accumulation of H2S in carbonate gas reservoirs may be associated with pyrite. In this paper, thermodynamic analysis and simulation experiments on the interactions between pyrite and water were carried out to investigate the possibility of pyrite hydrolysis in diagenetic environments. The results show that hydrolysis of pyrite possibly takes place above 275 o C. When temperature is above 425 o C, the reaction can proceed spontaneously. The temperature range favoring the occurrence of pyrite hydrolysis is far higher than that for typical oil and gas reservoirs. Thermodynamically pH has negligible influence on the formation of H2S during hydrolysis of pyrite in sedimentary basins. The results of our simulation experiments strongly imply that a small amount of pyrrhotite (FeS1.13) was formed during pyrite decomposition. Nevertheless, significant hydrolysis of pyrite did not occur under closed experimental conditions. Water may not act as an important hydrogen source for H2S generation in a typical natural gas reservoir.

Hydrogen Peroxide Ammonium Citrate Extraction: Mineral Decomposition and Preliminary Waste Rock Characterization

“…For example, in the cases of the samples WR1 and WR2, the HA2+AR2 S concentrations were only around half of the AR1 S concentrations. As the Fe-sulfide dissolution processes can produce H 2 S [52,53], it can be assumed that the S was lost due to gasification during the extraction.…”