Gamma Spectroscopy Logging And Spectrum Resolution Application Based On Controllable Neutron Source

Nowadays,the domestic consumption of oil and gas resources is increasing while the conventional oil and gas reservoirs are exhausted.However,due to the great difficulty of unconventional oil and gas development,it puts forward higher requirements for oil and gas exploration and production,demanding new logging and production methods.Gamma spectroscopy logging,a technology that uses neutrons to react with the nuclei of formation elements to measure and analyze the gamma carrying formation information,and then calculate the relative content of each element of the formation.In 1991,the Schlumberger company introduced and promoted the element capture spectrum logging tool,which can only obtain the content of seven elements(Si,Fe,S,Ca,Ti,Ba,Gd)and their combination's different mineral content.later,Schlumberger's Litho Scanner was launched in 2012 and it can measure inelastic scattering and captured gamma spectroscopy.This new scanner can not only obtain the carbon content,but also a variety of other element content with higher accuracy.Because of its high performance,Litho Scanner was widely used in the exploration and production of unconventional oil and gas reservoirs.The purpose of this thesis is to perform log interpretation analysis for the controllable source gamma spectroscopy logging.Based on Schlumberger's Litho Scanner,a logging model was set up by the MCNP(Monte Carlo N-Particle Transport Code)simulation method.In the model,the D-T pulsed neutron source using 4? solid angle emission neutrons was selected,also,the LaBr3: Ce detector was employed with its energy resolution set.To supplement the missing elements(Mg,Cl,K,Ti,Ge,Ba,Ce,La,Gd)and their isotope reaction cross sections in MCNP5,the NJOY2016 program was used,verifying the supplemented cross section data and determining the correctness of the cross section.At the same time,according to the comparison of the neutron reaction cross section,energy and reaction time of the element in the inelastic scattering reaction and the capture reaction,the methods aiming at processing the single element inelastic scattering gamma,the captured gamma neglecting the influence of inelastic scattering and the background gamma of captured gamma considering inelastic scattering were proposed,a better single-element inelastic gamma energy spectrum and captured gamma energy spectrum of the formation were obtained.On the other hand,the data processing method of controllable source logging energy spectrum using inelastic scattering and capture gamma energy spectrum was also studied.The results showed that 5-point Savitzky-Golay filter was the best method for smoothing the gamma energy spectrum,and the energy conversion relationship of the track site was determined.After that,peak-finding,spectral drift correction and spectral count normalization processing were carried out,by introducing a deduction factor that varies with the depth of the formation,a net inelastic scattering and a net captured gamma energy spectrum were obtained.In addition,the despreading method for this type of instrument was studied.The relative yield of various elements was calculated based on the single-element gamma energy spectrum,net spectrum and least square method,realizing the spectral analysis and comparison of the net inelasticity and net capture gamma energy.A good result of spectrum analysis was finally achieved.Throughout the thesis,from the perspective of theory and simulation,combining with the logging data obtained by actual logging,a complete process was used to study the gamma spectroscopy logging based on controllable sources,a good element relative yield was gained from it.The results in this thesis laid a foundation for further research on the analysis of controllable source gamma-ray logging.