--> ABSTRACT: Stable Carbon Isotope Reversal Does Not Correlate to Production in the Marcellus Shale, by Madren, Jonathan; #90142 (2012)

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Stable Carbon Isotope Reversal Does Not Correlate to Production in the Marcellus Shale

Madren, Jonathan *1
(1) Anadarko Petroleum Corporation, Conroe, TX.

Do trends in stable carbon isotopes correlate to production in shale gas plays? It has long been noted that the stable carbon isotopes of hydrocarbons such as methane, ethane, and propane tend to become isotopically heavier with higher thermal maturity. Recently, workers have encountered a reversal in this trend in several horizontal plays such as the Barnett Shale of west Texas and the Haynesville Shale in Louisiana. In these areas, the stable carbon isotopes of ethane and propane become isotopically lighter with depth, a reversal of the normal trend. While this trend could be interpreted as mixing of gases with different origin and maturity, the low permeability of these formations makes this unlikely. Although the mechanism of this reversal presently remains unclear, there is an association between the presence of this isotopic anomaly and increased production in some horizontal plays.

Using isotopes to predict areas of higher production was evaluated in the Marcellus Shale in western Pennsylvania. The results of this work indicate that stable carbon isotopes go through the same reversal process as in other plays, but the trends are the same in both areas of good and poor production. Rather than acting as a signal for higher production volumes, the reversal in isotopic trend is probably indicative of maturity and the stratigraphic horizon of this reversal is likely due to the occurrence of better seals within shale members seen throughout the Hamilton formation. Therefore, better production in the Marcellus Shale seems to be more closely related to traditional matrix parameters like porosity and permeability than trends in stable carbon isotopes.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California