Modeling analysis of environmental effects on accelerator porosity logging measurements

MNCP modeling of a new Accelerator Porosity Sonde tool was performed in an 8-in borehole and over the complete porosity range in order to investigate its epithermal neutron response to porosity and the most significant environmental variables that affect the porosity measurement, including tool standoff, temperature, and the formation lithology. The results obtained for limestone, sandstone, and dolomite formations are compared to experiments when possible. These calculations give a much better detailed understanding of the tool response sensitivity than the limited number of laboratory measurements available in each formation lithology. The numerical model of the tool allows other features such as the porosity sensitivity on the interdetector shielding material and engineering design compromises such as requirements for intrashield wiring channels or electronic ports to be fully evaluated.<>