Abstract: An Integrated Approach to the Petrophysical and Petrographic Evaluation of Low Resistivity and Low Contrast Pay Resulting from Complex Mineralogy in Clastic Reservoirs

A comprehensive interpretation of a resistivity log's response in such complex reservoirs relies upon a thorough understanding of interactive processes at the petrophysical and petrographic scale. The research objective is to identify and describe specific mechanisms of electrical behaviour that account for poorly described features of low resistivity and low contrast pay in reservoirs of mineralogical complexity. It also aims to enhance the range of descriptive information available from the standard electrical petrophysical measurements made in the laboratory. The study addresses both conjectural and experimental relationships between mineralogy, pore architecture and the petrophysics of electrical interaction in rock-fluid systems.

Sandstones of divergent diagenetic mineralogy are being investigated from various provenances, ranging from a poor quality, bioturbated gas reservoir in the North Sea, to Triassic sandstones hosting 'red bed' type mineralization from the Alderley Edge mines in Cheshire, England. These rocks provide a natural source of polymetallic mineralized sandstones in which to study electrical circuitry and conductive systems, and will assist in understanding analogous mineral assemblages in reservoir rocks.

All laboratory data will be integrated with wireline log information where available, to evaluate the resistivity response at different scales and depths of investigation. Petrographic studies include descriptions of texture, structure, mineralogy and pore system morphology by thin section, XRD, XRF and SEM studies. Petrophysical characterization includes formation factor, resistivity index, spectral impedance analysis, capillary pressure, pore size distribution and excess conductivity where relevant. 

AAPG Search and Discovery Article #90940©1997 AAPG Foundation Grants-in-Aid