Paper: Porosity Calibration Of Modern Porosity Logs And Oil Neutron Logs, Mabee Field, Andrews And Martin Counties, Texas

As a part of the reservoir characterization and for calculation of original oil in place, it is necessary to correct the porosity logs to the core data. The Mabee field has 800+ logs with a majority of them consisting of old gamma ray neutron logs. The modern porosity logs were calibrated to core porosity by crossplotting log porosity against core porosity. Linear regressions were constructed which are defined by the slope and the y-intercept. The linear regressions demonstrated excellent linear correlation. It was observed that location of the well or geology appears to be more important in the relationship between core porosity and log porosity than the logging company. A logging company utilizing the same tool and logging boreholes the same size across the field exhibited varying slopes and y-intercepts. Conversely, one well logged by two different companies obtained nearly identical linear regressions. 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 logs of the neutron deflection. Linear regressions were done for the log,, neutron deflection vs. core porosity over the gross pay. Linear regressions of the mean and maximum 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 was 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 log,, neutron deflection to porosity.