Modeling analysis of environmental effects on accelerator porosity logging measurements

This paper reports on MCNP modeling of a new Accelerator Porosity Sonde (APS) too that was performed in an 8-inch 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 formation lithology. The results obtained in 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