Study on near detector-source spacing of density logging based on X-ray source

[Background] It has become a new trend to use X-ray source instead of ¹³⁷Cs source in density logging for development of oil logging. [Purpose] This study aims to analyze the near detector-source spacing's change when using a lower energy X-ray source instead of ¹³⁷Cs source in density logging. [Methods] Monte Carlo simulation method is used to study the critical detector-source spacing of different energy X-ray sources during the formation of water saturated limestone with different porosity, in addition, the near detector-source spacing is analyzed according to those sensitivities of X-ray sources and ¹³⁷Cs source. [Results] Simulation results show that low energy X-ray source's critical detector-source spacing is shorter compared with ¹³⁷Cs source's density instrument. When the density sensitivity is the same, the near detector-source spacing of X-ray source is shorter than that of ¹³⁷Cs source. [Conclusion] This study provides a theoretical basis for the design of near detector-source spacing of instrument. (authors)