利用双伽马探测器确定孔隙度的蒙特卡罗模拟  

Monte Carlo Simulation of Determining Porosity by Using Dual Gamma Detectors

作　　者：张锋[1] 刘军涛 袁超[2] 贾岩[3] 于华伟[1] 

机构地区：[1]中国石油大学(华东)地球科学与技术学院,山东青岛266580 [2]中国石油勘探开发研究院,北京100083 [3]中国石油大港油田测试公司,天津300280

出　　处：《同位素》2013年第2期104-109,共6页Journal of Isotopes

基　　金：国家自然科学基金项目(40774058;40874065);国家重大油气专项(2011ZX0520-002);山东省自然科学基金(ZR2012DM002);中石油创新基金(2012D-5006-0302);中央高校基本科研业务费专项资金(10CX03001A)

摘　　要：现有地层元素能谱测井技术是利用241 Am-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241 Am-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62cm和35cm。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10cm,副屏蔽体约为5cm。通过蒙特卡罗模拟,为利用241 Am-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。Current formation elements spectroscopy logging technology utilize 241 Am-Be neu- tron source and single BGO detector to determine elements contents. It plays an important role in mineral analysis and lithology identification of unconventional oil and gas explora- tion, but information measured is relatively limited. Measured system based on 241Am-Be neutron and dual detectors can be developed to realize the measurement of elements content as well as determine neutron gamma porosity by using ratio of gamma count between near and far detectors. Calculation model is built by Monte Carlo method to study neutron gainma porosity logging response with different spacing and shields. And it is concluded that measuring neutron gamma have high counts and good statistical property contrasted with measuring thermal neutron, but the sensitivity of porosity decrease. Sensitivity of porosity will increase as the spacing of dual detector increases. Spacing of far and near detectors should be around 62 em and 35 cm respectively. Gamma counts decrease and neutron gamma porosity sensitivity increase when shield is fixed between neutron and detector. The length of main shield should be greater than 10 cm and associated shielding is about 5 cm. By Monte Carlo Simulation study, the result provides technical support for determining porosi- ty in formation elements spectroscopy logging using 24lAm_Be neutron and gamma detectors.

关 键 词：241Am—Be中子源 伽马射线 中子伽马孔隙度 优化设计 蒙特卡罗模拟 

分 类 号：P631.8[天文地球—地质矿产勘探] TL816[天文地球—地质学]