测井用X射线管发射机制的数值模拟研究OA

Formation density logging is one of the most important applications of nuclear techniques in hydro-carbon exploration and production.Conventional density logging tools typically employ 137 Cs radioisotope sources,which have radiation risks to environment and the operators.X-ray technology with controllable radiation charac-teristics has been widely used in nondestructive testing,medical imaging,and irradiation,therefore,replacing chem-ical radioisotope sources with X-ray tubes has become an important development trend for nuclear logging.The narrow borehole environment imposes strict constraints on both the size and the emission geometry of X-ray tubes used in logging tools.The emission mechanism of X-ray tubes designed for formation density logging is investiga-ted.A Monte Carlo method is used to simulate the generation of X-rays produced by high-energy electrons bom-barding the anode target.The effects of key design parameters including target angle,target material,and electron beam energy on the tube output characteristics and on the formation density response are systematically analyzed,and the quantitative relationships between tube voltage and beam current and the required density measurement ac-curacy are clarified.The results show that the anode target should be mounted such that the normal to the target plane is aligned with the X-ray emission direction,and the X-ray exit angle of the tool should be as large as possi-ble.Although different target materials produce distinct characteristic X-ray lines,the high-energy scattered compo-nent of the spectrum shows only minor variations.Considering both physical properties and excitation efficiency,tungsten is identified as the preferred target material.The tube voltage and electron beam current jointly control the accuracy of X-ray-based density measurements.To achieve a density measurement accuracy of 0.015 g/cm3 with tradi-tional instruments,the required electron beam intensities of the tube are 3.6 mA,0.8 mA,and 0.5 mA for the tube voltages of 150kV,250kV,and 350 kV,respectively.