Neutron Capture Gamma Ray Spectrum Processing Method And Preliminary Application In Elemental Capture Logging

The reserves of lithologic formation approximate to the reserves of structural-pool but it is difficult to evaluate the mineral and element content of the reservoir in quantitatively as the reservoirs have been much complex than before. Neutron-gamma spectroscopy logging to technology is promising. So far, there are three companies which grasp the element well-logging. They are Schlumberger, Halliburton and BakerHughes.Schlumberger provides well-logging services in China, and n-gamma formation elements well-logging is one of the project.ECS (Element Capture Spectroscopy) logging tool is developed by Schlumberger. The 241Am(a,n) Be is used as the neutron source and the BGO (Bi4Ge3O12) detector is used to probe the gamma ray which is released by the action between neutron and elements in the formation. The information of the mineral and element content of the reservoirs can be attained by analyzing the gamma spectrum. The elements,Al,Ca,Fe,K,S,Si,Ti are important in strata analysis, and they have large thermal neutron capture cross section and emit gamma rays by capture reaction.In this paper, we start from the basic principle of nuclear physics with the ideal model. We derived three key parameters of element capture spectroscopy, they are relative yield, sensitivity factor and formation factor. And we propose a set of neutron capture gamma spectrum processing method, including the pretreatment. A computer model on the basis of Monte Carlo N-particle (MCNP) Code is developed according to the Element Capture Spectroscopy logging which is used to simulate the gamma spectra what produced by the capture reaction between neutron and elemental nucleus about some elements. The spectral processing method is applied to the measured spectrum, obtained four wells formation elements content, proving this method.At last, the reliability of the gamma spectra simulated by the same model is verified through analyzing the mixed gamma spectrum produced by kinds of elements.We solve the measured spectrum of four well, finally the three parameters and elements content with depth are given. Because only the relative yield data, compared to solve the relative yield and relative yield of ECS data, the trend is basically the same, there are still differences in value, and analyzes the causes of the differences.