Study On Uranium Quantitative Correction Method For Uranium Fission Prompt Neutron-γ Fusion Logging

Uranium fission prompt neutron-γfusion logging technology is a relatively advanced uranium quantitative logging technology.It inherits the advantages of single neutron logging andγlogging technology,and abandons the disadvantages of each,such as low efficiency,high cost and long period.It can realize uranium quantitative interpretation quickly,accurately and conveniently,and has significant technical advantages compared with traditional uranium logging methods.In this paper,the current theories and methods of uranium quantitative interpretation in neutron logging and gamma logging,the causes and influencing factors of the error of uranium quantitative interpretation results are reviewed,and the theoretical basis of uranium fission prompt neutron-gamma fusion logging technology is briefly discussed.On this basis,the thesis focuses on the dead time of neutron detector of fusion logging instrument（UNL-H1）,the correction method of dual-energy neutron time spectrum,the influence of logging environment on dual-energy neutron time spectrum and the correction method.The research results will effectively improve the accuracy of quantitative interpretation results of uranium fission prompt neutron-γfusion logging.The main research contents and achievements are as follows:1)The influence of the time characteristics,count rate fluctuation and background value of dual-energy neutrons on the optimal period of uranium quantification was analyzed,the extraction method of dual-energy neutron time spectrum characteristic information was discussed,and the optimal period of uranium quantification was determined;2)The method of obtaining neutron detector dead time is studied.The principle,method and procedure of calculating dead time by pulse"double body source"method are explored,as well as the key technical points.The results show that the factors such as window size,distance between two windows and neutron count rate difference of two body sources have great influence on the dead time calculation results.The reasonable range of influencing factors is proposed,and the reasonable dead time of neutron detector of fusion logger UNL-H1 is obtained by using this method;3)A method of revising the dual-energy neutron time spectrum of the neutron-γfusion logging instrument was established by revising the calibration data of the standard model over the years,and comparing the calibration coefficients before and after the correction,the correctness of the method of calculating the dead time of the pulse"two-body source"and the practicability of the method were verified.The optimum dead time of UNL-H1 is 0.716μs;4)The neutron calibration and total gamma calibration of the neutron-γfusion logging instrument were carried out by using the standard model well measurement and simulation methods,and the corresponding neutron calibration coefficient and gamma calibration coefficient were obtained.According to the data analysis of the latest standard model logging,the neutron calibration coefficient is revised from 0.3003（0.01%e U/cps）to 0.4864（0.01%e U/cps）after the correction of the dead time,which is very close to the calibration coefficient of 0.4823（0.01%e U/cps）obtained by simulation.It further proves the rationality and validity of the method of obtaining dead time and correcting;5)Under the condition that the parameters are basically the same,the effects of logging environmental parameters such as dry hole diameter,casing material and thickness,water layer thickness,mud composition and density on the dual-energy neutron time spectrum and the correction methods are studied by using MCNP simulation and experimental verification.Although there are some differences in the correction expressions,However,the influence law of logging parameters on time spectrum and the trend of N_E/T（Epithermal neutron count/Thermal neutron count ratio）with logging parameters are similar;6)A complete set of correction function expressions for the influence of logging parameters on dual-energy neutron time spectrum is established.The uranium content of the model was calculated by combining the modified expression of logging parameters obtained by simulation and experiment methods with the calibration coefficient previously obtained,and the relative error was compared with the true value.The order of relative error was as follows:uncorrected calculated value>calculated value of simulation correction>the calculated value of the experimental correction（after the correction of the dead time）,proving the reliability and practicability of the method of determining and correcting the dead time once again effectively;7)The fusion logging instruments UNL-H1 and logger FD3019 were used to carry out practical application in a bare hole in a mining area,and the uranium grade interpretation results of the borehole and the equilibrium coefficient of uranium-radium were obtained after the measured data were corrected by the complete set of uranium quantitative correction methods,and then compared with the core analysis results respectively.From the actual results,the practicability of the neutron-γfusion logging method and the validity of the uranium quantitative correction method are preliminarily proved.