Natural Fractures in the Barnett Shale: Comparison of Fort Worth Basin and Delaware Basin Examples.

Julia Gale1

¹University of Texas

Natural fracture systems are important in shale-gas reservoirs in two different ways. In some shale reservoirs the most important effect of natural fractures is their tendency to reactivate during hydraulic fracture treatments. The second way that fractures can be important is that in some shales natural fractures do contribute to permeability without any reactivation. The presence or absence of appreciable fracture porosity is undoubtedly related to the specific structural diagenetic history for each shale. Understanding the natural fracture system is therefore fundamental to decisions about how to complete wells.

Using core and outcrop studies I review common fracture types and characteristics the in the Mississippian Barnett Shale from the Fort Worth Basin in north central Texas and the Permian Basin in West Texas. Fracture origin is considered in the context of host-rock composition, burial history, and diagenetic evolution. Fracture attributes in these two basins are markedly different. Steep, narrow, calcite-sealed fractures are present in many Barnett cores in the Fort Worth Basin. They are important because of their likely tendency to reactivate during hydraulic fracture treatments. By contrast, in the Delaware Basin there is evidence that many fractures are partly open. Thus, their importance for completions is different from those in the Fort Worth Basin.

AAPG Search and Discover Article #90097 © 2009 Tulsa Geological Society, Tulsa, Oklahoma

 

 

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