不同中子源下补偿中子测井仪关键参数的MCNP模拟.doc

毕业设计（论文） 题 目 不同中子源下补偿中子测井仪关键参数的MCNP模拟 英文题 Monte-carlo comparison of Compensated Neutron Logger pivotal parameters Under Various neutron source 学生姓名 专 业 核工程与核技术 班 级 指导教师 二零一一年六月 摘 要 补偿中子测井是利用中子与钻井周围岩石和井内物质相互作用，探测地层岩石及其孔隙流体的化学元素和含量的测井技术。当地层空隙度小，其单位体积含氢量就小，利用补偿中子测井时含氢指数识别油气层则不敏感，可以通过调整合适的屏蔽体厚度、近、远探测器间距Δr和中子源距r等参数，以提高补偿中子测井对含氢指数识别油气层的灵敏度。本论文便是利用蒙特卡罗方法对补偿中子测井仪模型关键参数进行数值模拟计算，得出如下主要结论：本次模拟得到252Cf和Am-Be中子源下各参数的变化规律为：⑴铅屏蔽体厚度取6cm时远探测器碳氧比值取得最大值。⑵中子源为252Cf、探测器间距大于25cm时，远探测器碳氧比值随探测器间距的增加而不变；中子源为Am-Be、探测器间距大于20cm时，远探测器碳氧比值随探测器间距的增加而不变。⑶252Cf和Am-Be中子源下，近探测器热中子相对注量率和远探测器γ相对注量率都随源距的增加而减小。⑷Am-Be中子源下远探测器碳氧比值在空隙度为25%时取得最大值，252Cf中子源下远探测器碳氧比值随空隙度的增大而减小。这一结果，在补偿中子测井仪研制过程中，对Δr和中子源距r等参数，减少测试时间，降低成本，人员安全等方面，concent of chemcial elements of pore fluid and rock .Compensated Neutron Logger(CNL) becomes less sensitive to Hydrogen Index(HI) in identification of oil/gas bearing layers when formation porosity is small due to the low hydrogen quantity per unit volume. This paper aims to investigate the relationships between the CNL response and its design parameters, such as lead shield thickness, near-to-far detector spacing, and source-to-detector spacing, using the Monte Carlo method. The main study results as follow: The Simulation shows the change conclusion of each parameter under 252Cf and Am-Be neutron source: ⑴,Far-detector Carbon-oxygen ratio Obtain maximum while the thickness of lead shielding is 6cm. ⑵For 252Cf neutron source and Detector spacing is More than 25cm,far-detector carbon-oxygen ratio is unchanged With the increase of detector spacing; For Am-Be neutron source and detector spacing is more than 20cm,far-detector carbon-oxygen ratio is also unchanged With the increase of detector spacing.⑶Under Am-Be neutron source, near-detector’s thermal neutron relative flux rates and far-detector γ relative flux rates are reduced as an increase in source distance. ⑷Under Am-Be neutron, far-detector c