瞬发中子测井的铀矿井眼实时校正方法研究

Real-time correction method of uranium mine caliper based on prompt neutron well logging

在铀资源勘查过程中,相比与传统自然γ测井,铀裂变瞬发中子测井以其"直接测铀"的优势节约了勘探成本,提高了探测效率。但该技术受井眼条件对源中子的慢化与吸收影响较大,必须进行现场校正,才能保证其解释结果的有效性。本文通过蒙特卡罗模拟手段,铀裂变瞬发中子测井探管内采用14 MeV的氘-氚(D-T)脉冲中子源,源距为30 cm,中子探测器均为^(3)He气体探测器,γ探测器为LaBr_(3)(Ce)探测器。通过模拟井径为110 mm、130 mm、160 mm的生产孔,研究井径与热中子俘获γ能谱的对应关系,将井眼大小的变化以俘获γ谱的氢峰计数率表征,用拟合函数表示氢峰计数率的变化规律,获得氢峰计数率与井眼大小的对应关系,并以此修正中子测井的解释结果。测试验证结果表明:井径的变化可由氢元素特征峰计数率表征。本文方法可降低因井眼变化对铀裂变瞬发中子测井的解释结果的影响,为提高铀裂变瞬发中子测井的可靠性奠定基础。

[Background]In the exploration of uranium resources,the prompt fission neutron logging method saves the exploration cost and improves the detection efficiency with its advantage of directly measuring uranium.However,this method is greatly affected by the moderation and absorption of source neutrons by the formation environment,and must be corrected on site.[Purpose]This study aims to reduce the impact on the caliper variation for prompt neutron well logging by making use of the captureγspectrum.[Methods]First of all,the corresponding relationship between caliper and thermal neutron captureγspectroscopy was analyzed by Monte Carlo simulation based on the facts of 14 MeV deuterium-tritium(D-T)pulse neutron sources with a source distance of 30 cm for the uranium prompt fission neutron logging tube,two ^(3)He gas detectors for neutron measurement,and one LaBr_(3)(Ce)detector forγspectrum acquisition.Well diameters of 110 mm,130 mm and 160 mm were taken as simulation holes.Then,the variation of caliper was characterized by the hydrogen peak count rate of the capturedγspectrum,and the variation law of the hydrogen peak count rate was represented by a fitting function.Finally,the corresponding relationship between the hydrogen peak count rate and the caliper variation was obtained for the real-time correction of uranium mine caliper.[Results]Simulation results results shows that the change of well diameter can be characterized by the characteristic rate of hydrogen.The proposed method can reduce the influence of caliper change on the interpretation results of uranium fission prompt neutron logging.[Conclusions]This method has the ability to improve the reliability of uranium fission prompt neutron logging.