Monte Carlo Simulation Study Of RAS Saturation Logging

The pulsed-neutron logging technology is the most effective method to evaluate the oil saturation in the cased-hole.In order to determine the remaining oil saturation,monitor remaining oil distribution pattern and find potential reservoirs and identify water flooded conditions,a similar pulsed-neutron logging tool(RAS)has been introduced.RAS saturation logging instrument integrates the C/O logging and neutron lifetime logging,which can measure abundant information of the formation.Further studying the response of the influence factors on C/O logging of RAS can lay a foundation for further research of data processing and interpretation method of RAS saturation logging.In the second chapter,the paper analyzes the logging instrument structure,the logging principle,the measurement modes,and discuss the main application range of RAS.The third chapter introduces the Monte Carlo numerical simulation technology and Monte Carlo simulation software MCNP-5.Then combined with RAS logging instrument structure,oilfield typical borehole environment and formation conditions and other information,a Monte Carlo simulation model for RAS inelastic scattering measurement model is established,and the inelastic scattering measurement mode of Monte Carlo calculation model is tested;Subsequently,Monte Carlo simulation technology is used to simulate the response of RAS inelastic scattering mode in different casing sizes,thickness of cement,formation lithology,formation oil density and shale content.The relation diagram of the ratio of C/O logging to the oil saturation and porosity under different measurement conditions is established;A detailed analysis of casing size,cement thickness,lithology,oil density and shale content change on the influence of C/O logging measurement of RAS,on the basis of quantitative research and qualitative analysis of the relationship between the value of C/O logging and the change of the size of casing,cement thickness,lithology,oil density and shale content.Research shows that the value of C/O logging of RAS decreases with the increasing casing size,and its reduction is directly proportional to the porosity.With the cement thickness increasing,the value of C/O logging of the water formation increases,and the value of C/O logging of oil formation value is inversely proportional to the porosity.When the cement thickness is less than 100mm,the effect of cement thickness on C/O logging is basically linear.With density of crude oil in the layer increasing,the value of C/O logging in the pure water layer is constant,the value of C/O logging in the pure oil layer increases,and the increase rate is proportional to the porosity.With the increase of shale content,the decreasing trend of C/O logging in pure water layer decreases with increasing porosity.The value of C/O logging in pure oil layer increases with medium and low porosity,but decreases with high porosity.In summary,the effects of casing size,cement ring thickness,formation lithology,formation crude oil density,and formation shale content on the value of C/O logging are the results of interactions between the corresponding influencing factors and porosity.The conclusions of this study can be applied to the study of C/O logging data processing methods and interpretation methods of RAS and other similar pulsed-neutron logging tools.