Application of Vitrinite Reflectance to the Woodford Gas-Shale Play in Oklahoma.

Brian Cardott1

¹Oklahoma Geological Survey

Several dissimilar Woodford gas-shale plays across Oklahoma constitute a natural laboratory on the influence of thermal maturity to economic gas production (excluding other important influences such as thickness, depth, and completion techniques). The plays span a thermal maturity range from oil window to upper gas window.

Success in the Barnett Shale gas play in Texas suggests that the highest gas rates are in the gas window (>1.4% vitrinite reflectance, VRo). Most of the Woodford Shale gas wells are >1.4%-<3% VRo in the western part of the Arkoma Basin with initial potential (IP) gas rates as high as 11.2 million cubic feet of gas per day (MMcfd). Thermal maturity in the eastern Arkoma Basin is as high as >6% VRo. A theory that gas composition dilution with CO2 is possible at high thermal maturities (e.g., >3.0% VRo) is untested for the Woodford Shale.

Oil window/gas window boundary (@1.15-1.4% VRo) Woodford Shale gas plays are on the western edge of the Arkoma Basin play (with IP gas rates <1MMcfd, although 4 wells <1.0% VRo had IP gas rates 1-2.1MMcfd) and on the Anadarko Basin shelf in western Canadian County.

Woodford Shale gas plays in the oil window include oil-producing wells in the Ardmore Basin in southern Oklahoma and biogenic-methane-producing wells on the northeast Oklahoma shelf in Wagoner County. Two wells in the Ardmore Basin have produced >1 billion cubic feet of gas with little or no oil production from naturally fractured Woodford Shale at @4,000 feet deep.

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

 

 

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