ABSTRACT: Porosity Calibration of Modern Porosity Logs and Old Neutron Logs

DULL, DENNIS W., Texaco Exploration and Production Inc., Midland, TX

As a part of the reservoir characterization and for calculation of original oil in place, one must correct the porosity logs to the core data. The Mabee field has more than 800 logs, with a majority of them consisting of old gamma-ray neutron logs.

The modern porosity logs were calibrated to core porosity by cross-plotting log porosity against core porosity. The linear regressions demonstrated excellent linear correlation. Location of the well or geology appears to be more important in the relationship between core porosity and log porosity than the logging company. Maps of slopes and y-intercepts were used to obtain the transforms for converting modern porosity logs to core porosity. The cased hole neutron porosity logs indicated that location was important, but that the logging company was equally as important. The slopes and y-intercepts were mapped by logging company.

The old neutron logs demonstrated a good inverse linear relationship between core porosity and the log10 of the neutron deflection. Linear regressions were done for the log10 neutron deflection vs. core porosity over the gross pay. Linear regressions of the mean and maximum log10 neutron deflection vs. the mean and field minimum porosity generated nearly identical slope and y-intercept. Thus, any of the neutron deflection curves could be transformed to porosity if the mean porosity were known. Mean porosities were mapped using

all core and transformed porosity logs over gross pay. These contoured values of mean porosity were used to generate a slope and y-intercept that would define the transform to convert log10 neutron deflection to porosity.

AAPG Search and Discovery Article #91018©1992 AAPG Southwest Section Meeting, Midland, Texas, April 21-24, 1992 (2009)