Monte Carlo Simulation On Pulsed Neutron Formation Multi-element Logging

In recent years,with the decline of conventional oil and gas production and the increasing demand for oil and gas at the same time,people began to pay attention to unconventional oil and gas reservoir exploration and exploitation,a new type of technology was born-formation element logging.Formation element logging is a neutron gamma logging technology using interaction with the release of ?-rays between neutron source and formation elements to determine the element content,and then evaluate the formation.As a new technology for comprehensive evaluation of reservoirs,formation element logging can be used to obtain the mineral composition of the strata,which has been widely used in the identification of complex lithology,has become an important means of unconventional oil and gas reservoir identification and depositional environment and shale gas reservoir exploration.After research,it was found that the current foreign mastery of the technology of the logging company has three,namely Schlumberger,Halliburton and Baker Hughes,and China's formation element logging started late,in order to break the foreign China's technology monopoly,in 2012,China successfully developed a layer of elemental logging prototype.However,there is no set of standard elements that can be applied to the actual logging,and there is a lack of a complete method and software for capturing energy spectrum analysis.The focus of this paper is to study the pure standard energy spectrum acquisition and energy spectrum analysis algorithm.In this paper,the theoretical calculation formula of logging is deduced from the principle of logging,and the platform logging model is established by Monte Carlo program MCNP.The influence of different types of detectors and logging parameters on the measured energy spectrum is studied,to obtain the ideal element standard spectrum.According to the formula,the three important parameters needed to solve the solution are the relative yield,the relative sensitivity factor and the formation factor.The least square method is used to describe the process of solving the three parameters in detail.Finally,by using the above spectral method,the standard spectrum of each element and the spectral spectrum of the mixed stratum were combined to determine the mass percentage of the formation element,and the accuracy of the solution spectrum algorithm was verified by comparison with the actual element content.The LaBr3: Ce crystal can be used as a detector to obtain higher measurement accuracy.The structural parameters of the logging tool are optimized to achieve the best detection response.The energy spectrum is processed by the energy spectrum data.The content of the elements obtained by the energy spectrum data processing is compared with the actual content,and it is proved that the feasibility of the proposed spectral algorithm is feasible.