Combination of Magnetic Resonance and Classic Petrophysical Techniques to Determine Pore Geometry and Characterization of a Complex Heterogeneous Carbonate Reservoir

GUY, WILLARD J., TIMOTHY R. CARR, EVAN K. FRANSEEN, SAIBEL BHATTACHARYA, and SCOTT BEATY

As part of a USDOE and industry funded Class 2 project within the Schaben Field, Ness County, Kansas, the Kansas Geological Survey has evaluated a combination of petrophysical tools for characterization of complex heterogeneous cherty dolomite reservoirs. Production in the Schaben Field is from the Mississippian (Osagian) cherty dolomite beneath a major Pennsyivanian-Mississippian uncomformity.

The petrophysical evaluation of three recently drilled and older wells within Schaben Field has included traditional core analysis, air-brine capillary measurements, thin section petrography, photography and relative permeability measurements. Significant new technology includes mini-permeameter, the PfEFFER wire-line log analysis plot (resistivity vs porosity); and magnetic resonance measurements on selected saturated and unsaturated core samples to determine the "effective" porosity, free fluid percentage, bound water percentage and irreducible water saturation.

The primary problem in the evaluation of Mississippian fields in Kansas is how to determine the "effective" porosity in a cherty dolomite with fine intercrystalline porosity and variable amounts of secondary vugular, moldic, micro and solution porosity. This study indicates that the majority of the dolomite reservoir with intercrystalline porosity is an effective oil reservoir while the dolomite reservoir with the more highly visual vugular porosity is not always well connected and may not be an effective oil reservoir. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.