INFLUENCE OF MATURITY AND ORGANIC MATTER TYPES ON HYDROGEN EXCHANGEABILITY AND CARBON AND HYDROGEN ISOTOPIC SIGNATURES: EXAMPLE FROM THE NEW ALBANY SHALE

A suite of New Albany Shale (Devonian and Mississippian) samples from the Illinois Basin containing different types of organic matter, with vitrinite reflectance (Ro) from 0.29 to 1.4%, has been analyzed using 13C CP-MAS, NMR, FTIR, carbon and hydrogen isotopic ratios, as well as organic hydrogen isotopic exchangeability (Hex). Thermal maturity was first specified via Ro, then evaluated using NMR and FTIR. There is a good correlation (R2 ~ 0.8) among all three independent parameters for thermal maturity. Carbon isotopic values of the kerogens range from –27.4 to –30.8‰ and do not correlate with either thermal maturity or with maceral composition. Values of delta D of isotopically nonexchangeable organic hydrogen range from –125‰ (Ro=0.29) to -67‰ (Ro=1.27) and exhibit a linear trend towards enrichment in deuterium with increasing maturity. This trend may indicate thermally mediated interchange between D-depleted organic hydrogen and relatively D-enriched formation water hydrogen. The abundance of exchangeable organic hydrogen decreases from 7.3% to 2.4% with Ro increasing up to 0.6%, followed by a reverse trend of increasing Hex up to 6.6% at higher Ro. No clear relationship has been noted between hydrogen exchangeability and hydrogen isotopic values and petrographic composition, (for example, proportions of alginite and amorphinite) of kerogen.