基于热中子计数比的可控中子源密度测井方法研究  

Research on Controllable Neutron Source Density Logging Based on Thermal Neutron Counting Rate

作　　者：周少恒 常博 陶应龙 郝丽娟 李亚洲 王芳 甘佺 凤麟核团队 Zhou Shaoheng;Chang Bo;Tao Yinglong;Hao Lijuan;Li Yazhou;Wang Fang;Gan Quan;FDS Consortium(Hefei Institutes of Physical Science,Chinese Academy of Sciences,Hefei 230031,China;University of Science and Technology of China,Hefei 230026,China;International Academy of Neutron Science,Qingdao 266199,China;Thinking Neutron Technology Co.,Ltd.,Hefei 230031,China;Shandong Key Laboratory of Neutron Science and Technology,Qingdao 266199,China;不详)

机构地区：[1]中国科学院合肥物质科学研究院,合肥230031 [2]中国科学技术大学,合肥230026 [3]中子科学国际研究院,青岛266199 [4]中科石金(安徽)中子技术有限公司,合肥230031 [5]山东省中子科学技术重点实验室,青岛266199 [6]不详

出　　处：《核安全》2024年第6期93-100,共8页Nuclear Safety

基　　金：安徽省科技重大专项“高性能油气勘探中子发生器工程化研发”,项目编号:201903c08020003。

摘　　要：研究基于可控中子源的地层密度测井方法,该方法已成为核测井的一种发展趋势。受地层环境的影响,氘氚中子源产生的次生伽马源是一个与快中子输运过程相关的动态分布,仅采用伽马探测器计数的密度方法精度较差。为提高地层密度测量的精确性,通过引入热中子计数比与快中子减速长度的映射关系,建立了一种基于近、远非弹性散射伽马射线计数比与近、远热中子计数比的可控中子源密度测井方法。首先采用理想岩层环境模型验证了本文方法中的非弹性散射伽马射线计数比和热中子计数比与密度的响应关系符合快中子在地层中的输运规律,同时验证了该方法在不同岩性下的适用性,结果表明在密度为1.7~2.8 g/cm^(3)的范围内偏差小于0.025g/cm^(3)。进一步,基于TopMC/SuperMC建立四探测器中子密度测井仪器与标准井模型开展了本文方法的应用研究,结果表明,在不同岩性和密度条件下本文方法计算得到的计算密度与真实密度的相对误差都小于2.5%,初步验证了本文方法拥有较好的精确度,且对地层岩性敏感性较低。In the evolution of nuclear logging,nuclear density logging,as a conventional logging method in the open hole logging,is used to quantify the formation porosity.The conventional density logging technique employs cesium-137(Cs-137)as a radiation source,which presents a radiation risks to health,safety,and the environmental(HSE).Therefore,the exploration of formation density logging methods based on controllable neutron sources has emerged as a developmental trend in nuclear logging.The fast neutrons generated by the deuterium-tritium(D-T)source undergo inelastic scattering reactions with nuclides in the formation,resulting in a secondary gamma ray source.Due to the influence of geological environment,the gamma ray source exhibit a dynamic distribution which are closely associated with the transport process of the fast neutron.Therefore,the accuracy of the density measurement method which relying solely on gamma detector counting is unsatisfactory during actual measurements;hence it becomes necessary to consider for neutron counting as a means of correction.To enhance the precision of formation density measurement,by considering the response relationship between inelastic scattering counting ratio,diffusion length of inelastic scattering gamma rays and fast neutron slowing-down length,a thermal neutron counting rate was introduced to correct the effect of fast neutron slowing-down length on inelastic scattering counting.And a controllable neutron source density logging approach based on the ratio of near and far inelastic scattering gamma ray counts and the ratio of near and far thermal neutron counts is established in this study.Firstly,an ideal rock environment model was employed,and it was used to validate the correlation between the inelastic scattering gamma ray count ratio and thermal neutron count ratio with density in the established methodology,which adheres to the transport law of fast neutrons within the formation.Simultaneously,the applicability of the method was confirmed across diverse rock types.The

关 键 词：氘氚中子源 地层密度测井 热中子计数 蒙特卡罗 

分 类 号：TE19[石油与天然气工程—油气勘探]