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X射线密度测井屏蔽体的蒙特卡罗模拟研究

Monte Carlo simulation analysis of X-ray density logging shields
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摘要 密度测井中使用可控X射线源替代137Cs放射源已经成为新的趋势。X射线源强度受靶基上高压影响较大,当高压为350 kV时,密度测量不确定度可以保持在0.01 g·cm-3。为探究适用于350 kV高压X射线密度测井仪器的屏蔽体材料及厚度等参数,利用蒙特卡罗方法研究了X射线穿过不同材料与厚度后的能谱及计数率;并且通过对0~0.15 MeV、0.15~0.35 MeV两个能窗相关响应关系的对比,分析了不同能窗中X射线衰减与探测器计数率差异的原因。另外结合四探测器X射线密度测井仪器实际结构,主要考虑了三部分粒子对探测器的影响,并通过MCNP模拟分析并设计了各部分屏蔽体的放置方式及最佳厚度。研究表明:X射线的衰减无论在高能窗还是低能窗,都随着屏蔽材料原子序数及厚度而增大。选择钨镍铁合金为四探测器X射线密度测井仪器模型的屏蔽材料;在基座与近源距探测器之间设置的屏蔽体厚度为1.75 cm,每个探测器之间放置厚度为0.2 cm的屏蔽体,探测器背部增加0.35 cm厚度的屏蔽体。本研究为X射线密度测井仪研制中的屏蔽材料和结构提供了设计理论和关键参数。 [Background]The use of controlled X-ray sources instead of 137Cs radioactive sources in density logging has become a new trend.The intensity of the X-ray source is substantially influenced by the high voltage on the target substrate,and the density measurement uncertainty can be maintained at 0.01 g·cm−3 when the high voltage is 350 kV.[Purpose]This study aims to analyze the parameters of the shielding material and thickness suitable for the 350 kV high-voltage X-ray density logging instrument.[Methods]The Monte Carlo method was used to analyze the energy spectrum and counting rate of X-rays passing through different materials and thicknesses.By comparing the correlation between the 0~0.15 MeV and 0.15~0.35 MeV energy windows,the reasons for the difference between the X-ray attenuation and detector count rate in different energy windows were determined.In addition,combined with the actual instrument model construction of the four-detector X-ray density logging instrument,the influence of the three parts of particles on the detector was primarily considered.The placement mode and optimal thickness of each part of the shield for detectors were analyzed and designed using Monte Carlo N-particle(MCNP)simulation.[Results]The simulation results show that the attenuation of X-rays in high-and low-energy windows increases with increase of atomic number and thickness of shielding materials.When tungsten nickel iron alloy is selected as the shielding material for the four-detector X-ray density logging instrument model,the suitable thickness of the shield between the base and the near-source detector is 1.75 cm.Meanwhile,to maintain the high voltage of X-ray generator at 350 kV,a shield layer with a thickness of 0.2 cm is placed between each detector,and a shield layer with a thickness of 0.35 cm is added to the back of the detector.[Conclusions]This study provides the design theory and key parameters for shielding materials and structures in the development of X-ray density logging tool.
作者 刘睿 于华伟 祝倩 岳爱忠 王虎 刘超卓 张倩文 杨树 祝林苛 张晓蕾 LIU Rui;YU Huawei;ZHU Qian;YUE Aizhong;WANG Hu;LIU Chaozhuo;ZHANG Qianwen;YANG Shu;ZHU Linke;ZHANG Xiaolei(National Key Laboratory of Deep Oil and Gas,China University of Petroleum(East China),Qingdao 266580,China;School of Geosciences,China University of Petroleum(East China),Qingdao 266580,China;Well Logging Technology Research Institute of China Petroleum Group Well Logging Co.,Ltd.,Xi'an 710077,China;School of Science,China University of Petroleum(East China),Qingdao 266580,China)
出处 《核技术》 EI CAS CSCD 北大核心 2024年第8期8-14,共7页 Nuclear Techniques
基金 山东省自然科学基金(No.ZR2022MD019) 中国石油天然气集团有限公司科学研究与技术开发项目(No.2021DJ3801) 中央高校基本科研业务费(No.22CX01001A-2) 中国石油大学(华东)探究性实验项目资助 中国石油集团测井有限公司十大科技项目中项目九"测井应用基础与前沿储备技术研究项目"(No.CNLC2022-9C)课题六"开放基金课题"(No.CNLC2022-9C06)资助~~。
关键词 可控源 X射线 密度测井 蒙特卡罗模拟 屏蔽体 Controllable source X-ray Density logging Monte Carlo simulation Shield
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