Design and Realization of Pulse Neutron Casing Well Logging

Abstract: To meet the urgent need of current oil field exploration, after carefully studying of the same kind of data acquisition instruments at home and abroad, we have developed a new one to measure reservoir oil saturation.Through a lot of experiments and computer simulation, we have mastered the ability to measure the inelastic scatter gamma rays spectrum after an earth formation of interest adjacent a well bore is irradiated pulsed neutron. Thus we can determine the oil saturation of the formation of interest. We have compared the performance and well logging responsiveness among serveral instruments and we make our minds to use NaI(Tl) crystal and photomultiplier tube as the probe for gama rays. To get rid of the noise , we redesigned our instruments' spacing and screen and get a good signal/noise.New pulsed neutron generator and spectrum-stablizing technology are adopted to insure the relibity of data acquisition. Stabilization of spectrum can be observed realy and the operater can adjust relevant parameters during a log.A long-spaced detector and a short-spaced detector are used in the instrument. The long-spaced detector explors the useful information of the formation. The short-spaced one is used for bohole correction. The whole vertical resoluction of the instrument is high.Many high speed elements like CPLD are used in this system.,The CPLD elements are used to design the contrl part of the downhole instrument. With use of CPLD, the deadtime is reduced, then the effection of to measurement is lessoned.The whole system communites with the surface via LDT mode. Master-slave singlechip system is adopted in the sytem. The master singlechip system receives commonds from the surface and transmits back some auxiliary parameters in M2 mode. It also sends out control commonds from master singlechip as well. CPLD and other intergrated circuits are managed by the slave singlechip system. Emition of pulsed neutron, acquisition and quantify of long spaced signal are completed. At last,the logging signal is transmitted to the surface system in M5 mode.This instrument make a breakthrough of its sort in our domestic market and can be substitute of the same kind abroad. With sharp reduction in buying and maintenace cost, effective use at wide ranges in our oil fields bearing geologic feature can be expected once combined with correspond well logging interpretation theory and technology. To consider the oil recovery ratio improvement and persistence development in oil fields exploration, applaying of this instrument can play great role…
Key words: pulse neutron casing well logging; pulsed neutron generator; oil saturation logging

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