Enhanced Semi-Empirical Modeling of Neutron-Gamma Density Logs Incorporating Pair Production Effects: Experimental Benchmarking for Improved Accuracy

This study introduces an improved model for neutron-gamma density (NGD) measurements, specifically designed to reduce the impact of pair production on density estimations. Using the MCNPX simulation software, the model simulates the interaction of the NGD tool with geological formations, focusing on the energy distribution of neutrons and gamma rays, and the effect of mudcake thickness on gamma flux ratios. The study investigates how varying hydrogen weight fractions, particularly those below 10%, influence gamma and neutron flux. The new model effectively mitigates errors caused by pair production, offering more accurate density estimations, especially for formations with low hydrogen content. Experimental benchmarking with a Cf-252 source was conducted to validate the simulation results, providing a comparison with real-world data. While the model demonstrates improved performance for materials with hydrogen content less than 10%, further refinements may be needed for high hydrogen fraction scenarios.