The Importance of Applying "Intuition Factors" to Reservoir Volume Calculations: A Case Study in Wilburton Field, Arkoma Basin, Southeastern Oklahoma

Laura L. Wray

Calculating or extrapolating accurate reservoir parameters for recoverable reserve determinations is often difficult. Average porosities determined from logs can be incorrect due either to tool resolution in thin beds, wellbore rugosity, or faulty tool calibration. Water saturation estimates can vary depending upon the availability of measured or calculated Rw values. Reservoir thickness and aerial extent are only as accurate as the isopach maps from which they are derived. Measured reservoir pressures can be low in tight gas formations due to inadequate build-up times. Only formation temperature and abandonment pressure are more reliable numbers.

Characterization of the Spiro Sandstone reservoir in Wilburton Field, southeastern Oklahoma, requires the utilization of various "intuition factors". Extreme heterogeneity resulting from both depositional and diagenetic variability presents problems in accurately assessing pore volume calculations. By relying upon a systematic approach which allows scientific intuition to be merged with measured reservoir parameters, it is possible to predict economic and uneconomic results of proposed infill drilling locations.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California