Maturation effects on absolute biomarker concentration in a suite of coals and associated vitrinite concentrates

摘要: Abstract Extensive bulk chemical and petrographic characterization of 37 coals vitrinite concentrates the Lower Kittanning seam (Carboniferous) from western Pennsylvania eastern Ohio shows that are compositionally similar represent a uniform organic facies. Geochemical differences among samples due to rank, with reflectances ranging 0.53 1.76%. The sample suite affords an excellent opportunity evaluate effects coal rank on range commonly used molecular indicators thermal maturity. Absolute concentrations constituents, rather than peak ratios, were determined based addition internal standards (5β cholane d10-anthracene) extractable matter prior separation by liquid chromatography. C29 ααα 20R 20S sterane isomers provide clues processes involved in apparent “sterane epimerization” reaction. isomer is initially present free state much higher isomer. With increasing evolution kerogen, both liberated kerogen proportionality 20S, resulting net increase (20R + 20S) ratio. There appears be little evidence for epimerization molecules state. Kinetic modeling epimer therefore requires more elaborate reaction scheme involving formative degradative reactions, as opposed simple A-to-B conversion. amount 1-MDBT remains constant over wide maturity range, signifying equal rates formation destruction this compound relative total EOM. 4-MDBT general maturity, most pronounced change occurring at maturities above about 1.3% Rm. ratio 4 1 MDBT (“MDR parameter”) particularly useful assessment elevated levels (e.g. light oil/condensate range). Some source-dependent parameters, such pristane/phytane, C 27 29 sterane, 4β(H)-eudesmane/8β(H)-drimane 30 hopane 23 cheilanthane , found function rank. changes occur (Rm > 1.1%), where these source take “marine” or “deep-water lacustrine” signature, even though there no depositional environment coaly At lower corresponding typical oil window, less pronounced, but may still affect attempts correlate crude immature its suspected rock. dependence “source” parameters should taken into account petroleum geochemical studies non-marine systems.