Hydrous heating experiments at 130°C yield insights into the occurrence of hydrogen sulfide and light alkanes in natural gas reservoirs

Organic Geochemistry
By: , and 

Links

Abstract

Improved understanding of the origin of produced volatiles from conventional reservoirs and unconventional source rocks is critical for petroleum exploration and production. A series of hydrous heating experiments using two immature Type II siliciclastic source rocks, Pennsylvanian Turner Mine shale (TMS) and Devonian New Albany Shale (NAS), at 130 °C over one to two years were conducted to assess gas generation at low temperature. Elemental sulfur (ES) was added to the NAS samples to evaluate the role of sulfur on thermochemical sulfate reduction (TSR). The produced volatile composition was investigated in situ using Raman spectroscopy at the end of the heating experiments. Results show that the two source rocks yield different types and concentrations of volatiles. Only CH4 and CO2 were detected following hydrous heating of the TMS source rock in contrast to CH4, C2H6, C3H8, and CO2 which were observed in experiments using NAS. Variations in the produced volatiles are likely the result of compositional differences within the respective source rock organic matter. Experiments involving ES show strong H2S signals that are likely due to the formation of H2S from the reaction of ES with water at 130 °C. H2S signals correlate with a greater relative concentration of CH4 and CO2 compared to experiments where ES was not added, on a time-normalized basis. The correlation between the presence of H2S and an increase in CH4 and CO2 concentration could indicate the occurrence of TSR. Here we propose that H2S in siliciclastic shale can be generated in the presence of ES at low temperatures via both disproportionation of ES into H2S and SO42–, and TSR. Our findings from this study provide experimental evidence that may aid efforts to interpret the origin of H2S in low-temperature sedimentary basins.

Study Area

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Hydrous heating experiments at 130°C yield insights into the occurrence of hydrogen sulfide and light alkanes in natural gas reservoirs
Series title Organic Geochemistry
DOI 10.1016/j.orggeochem.2019.103901
Year Published 2019
Language English
Publisher Elsevier
Contributing office(s) Eastern Energy Resources Science Center
Description Article 103901
Country United States
State Pennsylvania