A design of source spacing of the X-ray density logging tool based on numerical simulation

Background In recent years, with increased awareness of environmental protection and safety, the development of nuclear logging tools using non-chemical sources such as X-ray instead of chemical sources like 137Cs has become a new trend. However, X-ray source usually has a lower energy level compared to chemical source, therefore the measurement accuracy is hardly satisfying the demand of density logging tool. Purpose This study aims to investigates the detector spacing design of a X-ray source tool based on an existing multi-detector gamma density tool. Methods Based on a 215.9 mm diameter borehole filled with water where the logging tool was eccentrically placed in, Monte Carlo software Geant 4 was employed for the simulation of the X-ray density logging in the formation density range of 1.7~3.0 g∙cm-3. According to density sensitivity, detection efficiency and depth, a series of models of this logging tool with detector-to-source distance between 135 mm and 430 mm were simulated to analyze the detector responses. Finally, based on above data, the design of source spacing for detectors was determined for the X-ray density tool. Results The finalized tool includes three NaI detectors with detector-to-source distances of 160 mm, 270 mm, and 344 mm, respectively. Simulation results show that the maximum wall detection depth reaches 120 mm with the vertical resolution of 344 mm, and the density measurement accuracy is 0.014 g∙cm-3. Conclusions The feasibility of developing a potential X-ray density logging tool is validated by this study, providing reference for future design of nonchemical source density logging tool.