Kerogens reduction

Oxidation of Kerogen, Sulfate Reduction and Onwards to Methanogenesis ... 

Reservoirs of natural gas generally contain only small amounts of H2S, but in some cases contain 2-30% by volume H2S(g) (Hitchon et al., 2001 Worden and Smalley, 2001). Sources of this H2S include (i) degradation of sulfur-rich kerogen, (ii) breakdown of sulfur-rich crude oil, (iii) BSR, and (iv) TSR (Worden and Smalley, 2001 Machel, 2001). Bacterial sulfate reduction is generally limited to temperatures below — 80 °C,... 

Sulfur isotope studies have also provided insights into the transition from Archean low Po to higher values in the Proterozoic. In the same studies that revealed extremely low Archean ocean sulfate concentrations, it was found that by —2.2 Ga, isotopic compositions of sedimentary sulfates and sulfides indicate bacterial sulfate reduction under more elevated seawater sulfate concentrations compared with the sulfate-poor Archean (Habicht et al., 2002 Canfield et al., 2000). As described above, nitrogen isotope ratios in sedimentary kerogens show a large and permanent shift at —2.0 Ga, consistent with denitrification, significant seawater nitrate concentrations, and thus available atmospheric O2. 

Bacterial sulfate reduction appeeirs to proceed to considerable depths in marine sediments but rates computed from changes in interstitial water sulfate concentrations, with suitable corrections for diffusion and sedimentation, are generally orders of magnitude below those in surface muds (Goldhaber and Kaplan, 1975). Again, this probably reflects a depletion of utilizable organic matter in the deeper layers by microbial utilization and conversion to more intractable humates and kerogens. 

Reduction and Phenol Acid Depolymerization of Colorado Oil Shale Kerogen... 

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