脉冲中子密度测井中的γ场和中子场特性  

The Characteristics of Gamma Fields and Neutron Fields in Pulsed Neutron Density Logging

作　　者：程亮[1] 吴文圣[1] 何景枝[2] 

机构地区：[1]油气资源与探测国家重点实验室(中国石油大学(北京)),北京102249 [2]安徽省勘查技术院,安徽合肥230031

出　　处：《石油天然气学报》2014年第5期77-82,5-6,共6页Journal of Oil and Gas Technology

基　　金：油气资源与探测国家重点实验室项目(PRPZY2008-02);国家重点基础研究发展计划项目(2006CB202306)

摘　　要：中子场和γ场特性直接或间接影响脉冲中子密度的测量精度。应用蒙特卡洛数值模拟方法,计算了一个脉冲周期内,中子场和γ场的时间特性、空间特性和在地层中的衰减特性。由此得出,总中子时间谱和总γ时间谱均为方波,强度在中子脉冲停止后瞬间达到最大;非弹性γ强度在中子脉冲期间较为稳定。快中子场、非弹性γ场在脉冲期间以中子源为中心呈球状分布;脉冲停止后,强度峰值分布在以源为中点的圆环上。热中子场的强度峰值总是分布在以中子源为中点的圆环上。快中子场在介质相同时,孔隙度越大,衰减越快(气层除外);孔隙度相同时,介质的原子密度和含氢量越大,衰减越快;非弹性γ场的衰减受地层密度和孔隙度双重影响。The characteristics of gamma fields and neutron fields would directly or indirectly influence the measurement precision of pulsed neutron density. With Monte Carlo numerical simulation,the time characteristics,space distribution characteristics and attenuation characteristics for gamma fields and neutron fields were calculated in a pulsed period. Calculated results showed that total neutron time spectrums and total gamma time spectrums were all square waves,their intensities reached the maximum level at the moment of neutron pulse disappearing; inelastic gamma intensity was very steady in neutron pulse period. The fast neutron filed and inelastic gamma field presented spherical distribution. After the neutron pulse was ceased,their intensity apexes were distributed over a circle centering on source point. The intensive apexes of thermal neutron field are always distributed over a circle centering on source point; for the fast neutron field,when the porous media are the same except gas,the larger the porosity is,the faster the attenuation velocity is. When the porosity is invariable,the higher the atomic density and hydrogen bearing capacity are,the faster the attenuation velocity would be; the attenuation of inelastic gamma field is influenced by formation density and porosity.

关 键 词：脉冲中子密度测井 中子场 γ场 蒙特卡洛模拟 

分 类 号：P631.81[天文地球—地质矿产勘探]