Eagleford Shale-gas Study

Figure 1. Play area and structural controls

Figure 1. Play area and structural controls of the Upper Cretaceous Eagle Ford Shale of south, central, and east Texas.


The Upper Cretaceous (Cenomanian to Turonian) Eagle Ford Shale, currently one of the most active gas-shale plays in the world, extends ~400 mi from the Maverick Basin and adjacent western San Marcos Arch in South and Central Texas to the East Texas Basin (Fig. 1). Eagle Ford production started in late 2008, with wells in the deeper part of the play (>15,000 ft) delivering dry gas and updip wells producing wet gas and liquids. Eagle Ford wells, within 16 fields in 22 counties, each have EUR's of 200,000 to 400,000 BOE cumulative production. Average daily production per well among the top 20 Eagle Ford producers is 2,580 Mcfe. Shale thickness of the more organic-rich lower Eagle Ford, the primary target, is generally <200 ft, whereas that in the more calcareous, upper unit is <480 ft (Fig. 2). Exploration and production is rapidly expanding northward. 

STARR team research in the Eagle Ford play has focused on the integrated regional lithostratigraphic framework of the Eagle Ford and adjacent units throughout its play area (Fig. 3). The prime intent is to aid explorationists to more clearly define the Eagle Ford Shale's possible producing areas from our observations of the unit's depth, thickness, and general lithologic character across its total subsurface area of occurrence. A 3D seismic survey is currently being investigated to study faulting and possible amplitudes reflecting distribution of organic-rich intervals.

Figure 2. Schematic southwest-to-northeast cross section

Figure 2. Schematic southwest-to-northeast cross section spanning the Eagle Ford play area showing interpretation of playwide facies correlations.

Weakly laminated to massive, organic-rich calcareous mudrock

Figure 3a. Whole-core samples of the dominant lithofacies in the Eagle Ford Shale, Maverick Basin:  Weakly laminated to massive, organic-rich calcareous mudrock of the lower Eagle interval, the primary target of operators.

 Interbedded, burrowed, and laminated calcareous mudrock

Figure 3b. Whole-core samples of the dominant lithofacies in the Eagle Ford Shale, Maverick Basin: Interbedded, burrowed, and laminated calcareous mudrock of the upper Eagle Ford interval.

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