--> Abstract: Hydrocarbon Potential of Upper Cretaceous Shale Sections, Including the Eagle Ford, Woodbine and Maness Shale, Central Texas, by Thomas D. Bowman; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Hydrocarbon Potential of Upper Cretaceous Shale Sections, Including the Eagle Ford, Woodbine and Maness Shale, Central Texas

Thomas D. Bowman1

(1) TDB Oil Corp, Houston, TX.

Understanding the similarities and differences in any developing shale play is important as core acreage becomes leased and vigorous evaluation and understanding of these changes becomes important before extending a play and expanding the potential lease area. The Upper Cretaceous Shale section in Central Texas trends across Texas from the Mexican border in Southwest Texas into East Texas, roughly 50 miles wide and over 500 miles long. It is Upper Cretaceous in age resting between the Buda Lime and the base of the Austin Chalk. This section is referred to as the Eagle Ford shale in the Southwest Texas counties and is referred to as the Eagle Ford, Woodbine and Maness shale (Upper Cretaceous) of the East Texas counties. These formations are typically dark, organic-rich, brittle, fractured, fossiliferous, pyretic, and calcareous dark-grey to black shale. The generally, dark, organic-rich shale intervals exhibit increased natural radioactivity compared with lighter-colored shale that contain less organic matter. Referenced studies, both laboratory and natural, indicate gamma-ray spectral logging in open and/or cased wellbores indicate this increase in radioactivity to be primarily a result of increased uranium concentrations. Shale in the Eagle Ford/Woodbine/Maness formations attract radioactive isotopes of potassium, thorium and uranium, and can be characterized as falling into two categories: Dark, organically rich shale having radioactive characteristics of high potassium and high thorium, and having excessively high uranium content; and brittle, calcareous or silty, fractured shale that often produces oil and gas having a low potassium and thorium content with excessively high uranium response. The two kinds of log responses may have very similar total gamma-ray radiation, but the variation of the radioactive components that comprise the total gamma-ray response may be quite different when the components are broken down into their respective spectral concentrations. Changes these uranium, potassium and thorium percentages are most likely the response of regional changes in clay content. Across the play fairway from Southwest to East Texas these changes in clay content have been the major concern for hydrocarbon storage, drilling and completion techniques required for successful expansion of the Eagle Ford/Woodbine/Maness shale formations and resulting resource plays into east Texas and beyond.