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随钻过程中采用D-T可控中子源和2个NaI晶体探测器系统,记录两个探测器的非弹性散射和俘获伽马射线,采用俘获伽马计数比值进行含氢指数校正后,建立非弹性散射伽马计数比和地层密度的响应关系,从而实现脉冲中子-伽马密度测井.利用蒙特卡罗方法模拟地层条件下非弹性散射和俘获伽马分布,得到非弹伽马计数与地层密度和含氢指数都有关,但近、远探测器俘获伽马计数比反映含氢指数灵敏度高,利用其对含氢指数校正后就可以得到非弹伽马计数与地层密度的关系;通过二元回归方法得出地层密度校正后的响应公式,校正后视密度和真密度值相差很小.研究结果表明,在随钻过程中利用脉冲中子伽马测井方法可以确定地层密度.
DT controllable neutron source and 2 NaI crystal detector systems are used during the drilling process. The inelastic scattering and trapping gamma ray of two detectors are recorded. After hydrogen isotope correction is achieved by capturing gamma ratio, Elastic scattering gamma ratio and formation density in order to realize the pulse neutron-gamma density logging.Using Monte Carlo method to simulate the inelastic scattering and trapping gamma distribution in the formation, the non-elastic gamma count and The density of formation and the hydrogen index are related, but near and far detector capture gamma count reflects the high hydrogen index sensitivity, the use of its hydrogen index can be corrected after non-bomb gamma count and the relationship between the formation density; through The binary regression method yields the response formula of stratigraphic density correction, and the corrected apparent density and true density value have little difference.The results show that the density of stratigraphy can be determined by pulsed neutron gamma logging while drilling.