Zhao, Hank¹ 
(1) Republic Energy, Dallas, TX

ABSTRACT: Thermal Maturation and Physical Properties of Barnett Shale in Fort Worth Basin, North Texas

Intensive development with increasing large scale fracturing treatments has made the Barnett shale play in the Fort Worth Basin the largest shale gas field in the United States. The Mississippian-age Barnett Shale is both organic-rich gas source and fractured reservoir rock. Its thermal maturity and physical properties mainly along with porosity and brittleness are the most important factors for commercial gas production. 
Through analyzing digital data of hundreds of well logs basin-wide, a log-derived indicator of shale thermal maturity was established and correlated with measurement data and production data. On this basis, the various areas bearing either oil, condensate, wet gas, or dry gas in the Barnett Shale were delineated over the whole basin. It clearly indicates that gas occurrences are strongly associated with local thermal anomalies, instead of burial depth only. 
The physical properties of the shale are mainly determined by its porosity and brittleness. The study shows that lateral variation of shale porosity closely related with local structural relief of unconformably underlying Ordovician carbonate formations (Viola or Ellenburger) in scale and size. However, the regional structural dips have little affect on variation of the shale porosity. A concept of early differential compaction of Barnett shale between underlying and overlying carbonate formations was illustrated with several individual cases. The shale brittleness is an important factor for the shale to be fractured either by natural stress or by fracturing stimulation. It results from a combination effect of the rock composition related to local depositional environments and a degree of alignment of clay particles related to the differential compaction. 
Acknowledgements: Permission of Republic Energy; Helpful discussion with Brad Curtis and Dan Steward

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.