Geochemical Characterization of Gases from the Barnett Shale, Fort Worth Basin, Texas, by Norelis Rodriguez Maiz and R. Paul Philp
Molecular and isotopic composition of 53 gas and 7 condensate samples produced from the Barnett Shale were analyzed by gas chromatography isotope ratio mass spectrometry in order to determine the origin and maturity at which these gases were generated. Additionally, two hydrous pyrolysis experiments were carried out using immature outcrop samples with the objective of corroborating the maturity values predicted for the gases.
TOC and Rock-eval data measured on core and outcrop samples indicate the Barnett Shale primarily contains type II organic matter. Characterization using molecular, and C and D isotopic, composition indicates that gas produced from the Barnett is thermogenic in origin and does not appear to contain any biogenic gas.
Two main groups of gases were identified based on molecular and isotopic composition. Methyl adamantane index combined with vitrinite reflectance measurements, isotopic composition of the gases and the results from the hydrous pyrolysis experiments indicate a maturity range of 1.3 to 1.9 %Ro for group 2 gases. Values above 1.9 %Ro are suggested for group 1 gases, with the higher maturities in the areas closer to the Ouachita Thrust Belt. Finally, a general increase in maturity is observed from west to east in the Fort Worth Basin with higher maturity values near the Ouachita Trust Belt, possibly due to the effect of hydrothermal fluids on the burial history of the basin.
AAPG Search and Discovery Article #90070 © 2007 AAPG Foundation Grants in Aid