Type II-S kerogens

Figure 2a shows the total ion chromatogram (TIC) of the flash pyrolysate of a sulfur-rich (Type II-S) kerogen from the Jurf ed Darawish Oil Shale. The major peaks are alkylated thiophenes, shown more clearly in... 

Two Type II-S kerogens (as defined by Orr (i)) from the onshore Santa Maria Basin Monterey formation were pyrolyzed in this study to determine (a) the distribution of sulfur and its isotopic composition among the various products formed during artificial maturation, and (b) maturation trends reflected in the sulfur isotopic and elemental S/C ratios of kerogens, and in the variation of C and H isotopes. In addition, S isotopes in pyrites, kerogens and bitumens from the two Monterey shale samples were examined to speculate on the mode of S incorporation into Santa Maria Basin sediments. 

Most of the information on S S values of the reduced sulfur in sediments derives from both acid volatile sulfide (FeS) and pyrite (Fe 2). In a few cases, both sulfate and other sulfur species were isotopically compared. Due to analytical difficulties, organic sulfur and elemental sulfur isotope (S S) ratios were studied only in cases where the secondary enrichment led to OM rich in sulfur. This secondary enrichment forms type II-S kerogens. 

SELECTED CASE STUDIES OE TYPE II-S KEROGEN FORMATION ... 

This paper deals with the chemical and isotopic evolution of type II-S kerogen during its thermal maturation. 

Experimental thermal alteration (pyrolysis) provides the best opportunity to characterize changes in type II-S kerogen under thermal stress. In the present section, we follow the changes in sulfur isotope distribution as a result of the different temperatures and pyrolysis conditions. 

During the discussion on pyrolysis experiments we will refer to the Rock Eval thermal method, commercially used for the evaluation of PSR and maturation of sedimentary organic matter. This method employs an open system programmed pyrolyser purged with He carrier gas into various detectors for monitoring hydrocarbons, CO2 and a modified version with a sulfur detector. The use of this method for the evaluation of rocks containing type II-S kerogens is well documented (see Spiro, 1991 Baskin and Peters, 1992). 

Fig. 1. Sulfur isotope fractionation during closed vessel pyrolysis of several immature type II-S kerogens. This figure is after Everlien et al. (1997). The ratios reported as difference between values...

Sinninghe Damst6 J. S., de las Heras X. C. and de Leeuw J. W. (1992) Molecular analysis of sulfur-rich brown coals by flash pyrolysis-gas chromatography mass-spectrometry the type-II-S kerogen. J. Chromatogr. 607, 361-376. 

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