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The AAPG/Datapages Combined Publications Database

Wyoming Geological Association


Resources of Southwestern Wyoming; Field Conference Guidebook, 1995
Pages 271-280

Improvements to Formation Evaluation, Almond Formation, Green River Basin, Wyoming

William P. Iverson, Thomas L. Dunn, Ronald C. Surdam


Almond sandstone cores from an Amoco well at the north end of the Echo Springs gas field are used to measure petrophysical properties in the laboratory. Permeability (Kg) versus confining stress verifies a slight reduction of Kg at in situ conditions. The cut-off porosity of 12% used commonly by many operators is verified with these data. Brine saturated core samples also verify the commonly used sandstone Archie parameters of a = 0.81 and m = 2.0 for calculating resistivity formation factors. The saturation exponent is accurately determined at n = 2.0 for use in Archie's equation. Such data support calculations of gross gas-in-place from volumetric techniques using well logs. Capillary pressure curves obtained with mercury injection techniques demonstrate the expected threshold displacement pressures, high in the tight sands and lower in the more porous sands. Effective permeability to gas (ke) is also determined at irreducible water saturation, and found to be very reduced in the tightest samples. More porous sands show little reduction in ke in comparison with previous kg measurements. These data improve our database for the Almond sandstone and allow for improvements to formation evaluation in general.

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