Research On Fast Calculation Method Of Neutron Logging Based On Detection Range Constraint

Due to the complex lithology of unconventional reservoirs,field interpreters often rely on logging simulation models to provide a basis for interpretation.Monte Carlo method is one of the main techniques used in simulation to obtain nuclear detection responses in complex environments.However,this method requires a large number of random samplings,which is computationally expensive and not suitable for real-time logging interpretation.Thus,it is crucial to develop a fast forward calculation method to overcome the limitations of Monte Carlo methods.In this thesis,a new method based on perturbation theory is proposed to compute detector responses in various complex environments.The method uses environmental perturbations constrained by detection range to achieve at least six orders of magnitude faster computation than Monte Carlo methods.Extensive model data are used to validate the reliability of the proposed method,demonstrating consistency with Monte Carlo method results.The proposed method is applied successfully to the inversion of earth model parameters and tool improvement.The modularization and softwareization of the related methods are implemented,and a functionally integrated software platform is developed to make automated application of the fast forward calculation methods.Thesis first presents the theoretical basis of neutron logging,including the neutron transport process,neutron diffusion flux,and conventional environmental correction algorithm.Next,the Monte Carlo neutron porosity logging simulation model is developed based on the actual neutron tool CNT-100,and its accuracy is verified through experiments on numerous test pits.Then,based on theories and simulation model,the environmental influences in the well are analyzed,and a complete database is constructed for the development of the fast forward calculation method.Subsequently,thesis combines perturbation theory and neutron transport theory to develop the fundamental numerical model of detector response for neutron porosity logging.The numerical model is optimized by incorporating the detector detection range of the actual tool,and the fast forward calculation method is developed by using the database.The effectiveness and speed of the fast forward calculation method are verified in four simulation cases.In two actual field well cases,the Earth model parameters obtained from the inversion corresponded well with the interpreted model,validating the applicability and reliability of the inversion method based on the fast forward calculation.Furthermore,based on the data support provided by the fast forward calculation method,tool is improved,and a multi-chart calibration algorithm is proposed to enhance porosity measurement accuracy.Finally,thesis paper modularizes and softwareizes the related methods of migration length calculation and fast forward calculation based on the research results.The logging model calculation module,nuclear physics parameter calculation module,data processing module,fast forward calculation module and inversion algorithm module are constructed on a functionally integrated software platform.This platform simplifies the process of developing fast forward calculation method and automates its application.