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STARR New Venture Regional Studies

Barnett Shale-gas Play Analysis


The Mississippian Barnett Shale of the Fort Worth Basin (FWB) (figure 1) is a “shale-gas” system composed of a mixture of laminated siliceous mudstone, laminated argillaceous lime mudstone (marl), and skeletal argillaceous lime packstones. Newark East field, the largest gas field in Texas, is developed in this Barnett “shale-gas” system. The Barnett Formation continues to be an active target for shale gas in the FWB, as well as in the adjacent Permian Basin. Much effort has been devoted to understanding exploration methods, completion techniques, organic content, and maturation in this system. However, little has been published on the sedimentology, lithofacies, or depositional setting of these rocks. To help maximize the resources from this shale-gas system, The STARR Program has been studying the Barnett strata using wireline logs, cores, and outcrops. Research efforts are underway to understand the regional depositional setting, lithofacies, and pore networks (fractures and nanopores). This effort will help define exploration limits of production and provide data for defining completion techniques.

Data used:
Well logs – correlations
Cores – facies, porosity, and diagenesis (core example)
Literature – background informationProduction/Engineering data – best producing intervals and sweet spots

Figure 1. Outline of the Fort Worth Basin showing tectonic elements and core distribution.

Wise, Montague, Cooke, Clay, Denton, Jack, Palo Pinto, Parker, Hood, Erath, Somervell, Bosque, Hill, Johnson, Tarrant, Ellis, Dallas

Figure 3. Cold-cathode CL, plane light, and EDS element map images of multiple fracture sets in the dolomitic layer. Early, middle and late labels refer to the relative timing of fractures. Phases are labeled albite (a), barite (b), calcite (c), dolomite (d), pyrite (p) and quartz (q). (click picture to enlarge)
Figure 2. Natural fractures in the T. P. Sims core sealed with calcite and arranged in en echelon arrays at (a) meter and (b) centimeter scale. (c) Broken fracture surface showing calcite mineralization. Note that subtle changes in host-rock composition are reflected in differences in character of cement. The numbers on the core are depths in feet. (click picture to enlarge)  

©2008 Bureau of Economic Geology, The University of Texas at Austin