Numerical Simulation on Pulsed Neutron-Gamma Ray Density Logging Response in Logging while Drilling

The inelastic and capture gamma ray at different spacing can be recorded with the system of D-T pulsed neutron source and two NaI crystal detectors. The response of inelastic gamma ray counting ratio from near and far detectors and formation density can be obtained after hydrogen index was corrected by the capture gamma ray counts ratio. As a result, the formation density can be measured with pulsed neutron-gamma logging method. The distributions of inelastic and capture gamma ray under different formation conditions are simulated using Monte Carlo method, and then the inelastic gamma ray counting is related to formation density and hydrogen index. Owing to the higher sensitivity of capture gamma ray reflecting to hydrogen index than inelastic gamma ray, the response of formation density and the inelastic gamma ray counting ratio from near and far detectors is founded, which hydrogen index is corrected by capture gamma ray counting. In addition, the binary regression method is utilized to get the density response formula, with which the apparent density after correction is very close to the real one. It is concluded that the formation density can be determined by pulsed neutron gamma logging method while drilling.