Study on the dual gamma spectrum saturation logging method based on pulsed neutron source and numerical simulation

The dual gamma spectrum saturation logging based on pulsed neutron source is a new technology that can at the same time record inelastic scattering and capture gamma ray spectra, along with gamma ray time spectrum at the far and near gamma ray detector by means of a special pulse and measurement timing design. It is found that counting statistics of inelastic scattering and capture gamma ray is superior to foreign instruments by using large-diameter instrument and BGO crystal detector. The gamma ray time spectrum after repeated pulse neutron emission still meets the exponential decay law, and the channel count of gamma ray time spectrum is cumulated, so its counting statistics is better than conventional neutron lifetime logging. In addition, the macroscopic absorption cross section obtained by this pulse and measure timing is nearly the same as the single pulse. It is found that the oil saturation can be determined with the cross-plot technology of C/O and formation macroscopic absorption cross section under the condition of unknown formation porosity.