JOHN H. DOVETON
Kansas Geological Survey, Lawrence, Kansas 66047

Abstract: Forward-modeling of Log Responses from Rock Petrophysical Properties as an Aid in Reservoir Analysis

Traditional log analysis is an inverse procedure in which an interpretation of reservoir fluid volumetrics and pore properties is made from indirect physical measurements of a logging tool. When logged zones from a well reservoir interval are plotted on a Pickett resistivity - porosity crossplot, they form a trajectory whose trace is dictated by petrofacies and relative height in the hydrocarbon column. The trajectory graphs the log response ?effect? rather than the reservoir variables because?, so that multiple interpretations can be possible when attempting the inverse path from log response effect to reservoir cause. Even when correct, the interpretation of reservoir properties is usually limited to a qualitative assessment rather than a quantitative characterization. Forward-modeling offers the alternative strategy in which reservoir models of capillary pressure can be converted to logging measurements and plotted on a Pickett plot for comparison with measured data. Forward-modeling provides realizations rather than solutions, and so must be viewed as critically as traditional inverse interpretation techniques. However, the models are generated from numerical rock measurements, so that useful reservoir characterizations can result from good matches of model to logging data. An ideal strategy combines both inverse interpretation and forward modeling within an integrated analysis.

AAPG Search and Discovery Article #90921©1999 AAPG Mid-Continent Section Meeting, Wichita, Kansas