Print this pageThe Relationship of Thermal Maturity and Structural Geology to Produced-Gas Composition in the Barnett Shale, Fort Worth Basin
Randy F. LaFollette1, Kent A. Bowker2, Hank Zhao3, and Daniel M. Jarvie4
1BJ Services Company, Tomball, TX
2Bowker Petroleum, LLC, The Woodlands, TX
3Independent Geologist, Dallas, TX
4Humble Geochemical Services, Humble, TX
Over the past few years the Barnett Shale of the Fort Worth basin has developed into the premier shale-gas play in the world. Accordingly, this play is utilized widely as a model for other prospective shale-gas plays. One of the key factors to the success of the Barnett, and, by extension, other gas-shale plays based on a Barnett analogue, is a complete understanding of the composition of the hydrocarbons in place (presumably some type of gas). Various techniques are employed to estimate the composition of the gas in place; and most of these techniques are based on a measurement of thermal maturity because, for the most part, thermal maturity determines the gas composition (given the precursor kerogen, etc.).
Detailed gas-composition data is not publicly available for production in Texas, but the state requires gas gravity data be collected yearly from each producing well. There are now thousands of producing Barnett wells in the Fort Worth basin. In the Barnett, there is an excellent correlation between the calorific content of the produced gas and its gas gravity. From the calorific content, we can infer a general gas composition. In general, gas gravity decreases (lower BTU) towards the Ouachita Front, but there are multiple localized trends in the gas-gravity data that appear to be related to faulting in the basin. There is good agreement between the gas gravity and a published map of the Barnett thermal maturity as measured by vitrinite reflectance and a map of maturity based on a published log-analysis technique. The data support the hypothesis that hot brine flowing in the underlying Ellenburger had a large influence on the thermal maturity of the Barnett.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas