Relationship Between Bitumen Maturity and Organic Facies in Devonian Shales from the Appalachian Basin

Alan R. Daly

Variation in several bitumen maturity parameters was studied in a core of Devonian shale from the central Appalachian basin. Kerogens in the shales are at maturity levels equivalent to the early stages of oil generation and range in composition from Type III-IV to Type II-III. Maturity parameters based on steranes, terpanes, and n-alkanes exhibit fluctuations that are unrelated to thermal maturity changes in the core. The parameters correlate with one another to a high degree and appear to be directly or indirectly related to the organic facies of the shales. The maturity level indicated by each parameter increases with total organic carbon (TOC) content and hydrogen index value. The greatest variation occurs in rocks with TOC values below 2% and hydrogen index values bel w 250. The data provide a good opportunity to examine the dependency of bitumen maturity on organic facies, and they highlight a caveat to be considered during interpretation.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.