Data-processing methods for D-T source neutron-gamma density logging while drilling

摘要: With the increasing demand for controllable source logging, research on data-processing algorithms that meet accuracy requirements has become key to the development of controllable-source-logging tools. This study theoretically derives the relationship between the formation density and inelastic gamma count rate to investigate the data-processing methods for deuterium-tritium (D-T) source neutron-gamma density logging while drilling. Then, algorithms for the net inelastic gamma count-rate extraction and neutron transport correction are studied using Monte Carlo simulations. A new method for fast-neutron effect identification and additional correction is proposed to improve the density-calculation accuracy of gas-filled and heavy-mineral formations. Finally, the effectiveness and accuracy of the proposed data-processing methods are verified based on simulated and measured data. The results show that the density-calculation accuracy of water-bearing conventional formations in simulated data is ±0.02g/cm3. The accuracy of gas-filled and heavy-mineral formations after the additional fast-neutron effect correction is ±0.025g/cm3. For the measured data from the actual tool, the algorithms per form well in the density calculation. The density results obtained using the processing algorithms are consistent with the density data provided by NeoScope. Therefore, the D-T source neutron-gamma density-logging algo rithms proposed in this study can obtain relatively accurate data-processing results for a variety of formations. This study provides technical support for engineering applications and the development of logging tools for controllable-source neutron-density logging.