Tongwei Zhang Paul G. Kralert Yongchun Tang Geoffrey S. Ellis 2019 <p><span>Although sulfur-containing compounds are known to play a significant role in the diagenic and catagenic processes that generate oil and gas, relatively little is known about the kinetics of reactions between elemental S and petroleum hydrocarbons. To investigate this subject, a series of closed-system pyrolysis experiments using paraffin, a low-sulfur oil, and a high-sulfur oil with and without elemental S were conducted, and first-order chemical kinetics were fit to the experimental results. The average value for the activation energy required to reduce elemental S to H</span>₂<span>S and to thermochemically alter higher molecular weight hydrocarbons to methane was calculated to be 193 kJ mol</span>^-1<span>&nbsp;(46 kcal mol</span>^-1<span>). The results of this study demonstrate that under typical geologic conditions the rate of reduction of elemental S to H</span>₂<span>S by petroleum hydrocarbons is quite rapid. The maximum time for substantial amounts of elemental S to persist in contact with petroleum hydrocarbons is estimated to be no more than a few million years in cool reservoirs (e.g., &lt;80 °C), and in hotter reservoirs (e.g., &gt;120 °C) the half-life of elemental S may be as short as hundreds of years. Additionally, the presence of elemental S substantially lowers the onset temperature of hydrocarbon thermal chemical alteration (TCA). The activation energy for TCA of a low-sulfur oil to generate methane is estimated to be lowered by 92 kJ mol</span>^-1<span>&nbsp;(22 kcal mol</span>^-1<span>) due to the presence of elemental sulfur. Consequently, the presence of elemental S in petroleum reservoirs is expected to lower the thermal stability of oil and decrease the maximum depth at which oil occurs within a basin (thermal deadline). The observed acceleration of hydrocarbon TCA is possibly due to organic sulfur compounds (e.g., thiols and sulfides) that form through the reaction of H</span>₂<span>S or polysulfides with hydrocarbons and subsequently thermally degrade leading to the formation of sulfur radicals that in turn enhance TCA reactions.</span></p> application/pdf 10.1016/j.gca.2019.02.023 en Elsevier Kinetics of elemental sulfur reduction by petroleum hydrocarbons and the implications for hydrocarbon thermal chemical alteration article