Monte Carlo Simulation of Determining Porosity by Using Dual Gamma Detectors

doi:10.7538/tws.2013.26.02.0104

Abstract

Abstract:

Current formation elementsspectroscopy logging technology utilize ²⁴¹Am-Be neutron source andsingle BGO detector to determine elements contents. It plays an important rolein mineral analysis and lithology identification of unconventional oil and gasexploration, but information measured is relatively limited. Measured systembased on ²⁴¹Am-Be neutron and dual detectors can be developed torealize the measurement of elements content as well as determine neutron gammaporosity by using ratio of gamma count between near and far detectors.Calculation model is built by Monte Carlo method to study neutron gamma porositylogging response with different spacing and shields. And it is concluded thatmeasuring neutron gamma have high counts and good statistical propertycontrasted with measuring thermal neutron, but the sensitivity of porositydecrease. Sensitivity of porosity will increase as the spacing of dual detectorincreases. Spacing of far and near detectors should be around 62 cm and 35 cmrespectively. Gamma counts decrease and neutron gamma porosity sensitivityincrease when shield is fixed between neutron and detector. The length of mainshield should be greater than 10 cm and associated shielding is about 5 cm. ByMonte Carlo Simulation study, the result provides technical support fordetermining porosity in formation elements spectroscopy logging using ²⁴¹Am-Beneutron and gamma detectors.

Key words: ^{font-family: 'Times New Roman'">241}font-family: 'Times New Roman'">Am-Be neutron source, gamma ray, neutron gamma porosity, optimaldesign, Monte Carlo Simulation

摘要：

现有地层元素能谱测井技术是利用²⁴¹Am-Be中子源和单BGO探测器确定元素含量，在非常规油气勘探的矿物分析和岩性识别方面发挥了重要作用，但信息相对单一。开发基于²⁴¹Am-Be中子源和双BGO探测器的测量系统，可在实现元素含量测量的同时利用近远探测器伽马计数比确定中子伽马孔隙度。本研究利用蒙特卡罗方法建立计算模型，模拟研究不同源距、屏蔽体等条件下中子伽马孔隙度测井响应，结果表明：与探测热中子相比，伽马射线计数率高、统计性好，但孔隙度的灵敏度下降；增加两个探测器的间距时灵敏度增加；远、近探测器源距选择62 cm和875px。中子源和探测器处放置屏蔽体，伽马计数下降，中子伽马孔隙度的灵敏度提高，主屏蔽体长度大于10 cm，副屏蔽体约为125px。通过蒙特卡罗模拟，为利用²⁴¹Am-Be中子源和伽马探测器的地层元素能谱测井中确定中子孔隙度参数提供技术支持。

关键词: ^{font-family: 'Times New Roman'">241}font-family: 'Times New Roman'">Am-Befont-family: 宋体">中子源font-family: 'Times New Roman'">, font-family: 宋体">伽马射线font-family: 'Times New Roman'">, font-family: 宋体">中子伽马孔隙度font-family: 'Times New Roman'">, font-family: 宋体">优化设计font-family: 'Times New Roman'">, font-family: 宋体">蒙特卡罗模拟

ZHANG Feng;LIUJun-tao;YUAN Chao;JIA Yan;YU Hua-wei. Monte Carlo Simulation of Determining Porosity by Using Dual Gamma Detectors[J]. Journal of Isotopes, 2013, 26(2): 104-109.

张锋;刘军涛;袁超;贾岩;于华伟. 利用双伽马探测器确定孔隙度的蒙特卡罗模拟[J]. 同位素, 2013, 26(2): 104-109.

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