Abstract: Neutron porosity logging is indispensable for hydrocarbon reserve estimation, reservoir evaluation, and development planning. The use of controllable D-T neutron sources in logging-while-drilling (LWD) offers a safer, more stable, and environmentally friendly solution, representing the future direction of the technology. This study investigated the neutron field distributions under various drill collar sizes, tool mounting positions, and measurement environments through Monte Carlo simulations, targeting both offshore and onshore applications. The response characteristics of neutron porosity logging under different drill collar conditions are systematically analyzed. Results showed that side-mounted tools offer significantly improved sensitivity and accuracy compared to center-mounted configurations. The trend of thermal neutron count ratios increasing with porosity remains consistent across different borehole and formation environments, though the relative sensitivity decreases with increasing porosity. The effect of measurement conditions on thermal neutron counts varies with drill collar size, with borehole diameter identified as the primary influencing factor. These findings indicate that variations in hydrogen content have a far greater impact on count ratio responses than differences in capture cross-section. Due to the combined effects of neutron moderation and capture, environmental influences differ notably across drill collar configurations. Therefore, targeted correction methods are required to ensure accurate D-T source neutron porosity logging in LWD operations.