Study On The Responses And Correction Methods Of Pulsed Neutron Porosity Logging

The pulsed neutron source logging is gradually replacing the chemical neutron source and gamma source logging because of environmental protection.It's now becoming the main method of logging.The measurement accuracy of pulsed neutron porosity logging is seriously affected by borehole and formation environment.Therefore,it is necessary to investigate the influence factors and correction methods for pulsed neutron porosity logging.In this paper,Monte Carlo numerical simulation software is used to establish the model of the pulsed neutron porosity logging instrument.The neutron porosity logging responses of pulsed source and Am-Be source were obtained.The logging responses under various influencing factors were obtained by changing the formation and borehole environment.The correction charts of several main influencing factors were made based on the standard well curve.At the same time,the article adopted the appropriate formulas to fit the porosity correction volume through the analysis of the porosity errors produced by various influencing factors,and obtained the correction formula of each influencing factor.The results showed that the pulsed neutron source had lower porosity sensitivity than Am-Be source.The density correction could effectively improve the porosity sensitivity of the pulsed neutron source,and even higher than that of the chemical source in low porosity formation.The simulating results displayed that some factors had great influence on the measurement results such as borehole diameter,standoff,borehole salinity,formation temperature and?_ma.While other factors had little effect such as mud density and mudcake thickness.The correction charts and correction formulas could effectively reduce the measurement errors caused by environmental factors and improve the measurement accuracy.