X射线密度测井能谱分析及响应特性研究

Energy Spectrum Analysis and Response Characteristics of X-Ray Density Logging

X射线源用于地层密度测井可避免放射性危害,对实现核测井的无源化具有重要意义。针对137 Cs源和X射线源产生的射线在不同介质衰减差异进行分析,利用蒙特卡罗方法模拟X射线能量、源距、地层密度和泥饼等条件下的能谱及响应,并对比研究2种射线源在改变岩性、地层密度、井眼环境等因素时的差异。研究结果表明,X射线散射能谱与源能量和源距等因素有关,进入地层发生反散射会出现双峰现象,且随着源距增加变为单峰;X射线光电效应过程明显,受岩性影响更大,且地层密度灵敏度大于137 Cs源;超近探测器计数信息可计算泥饼密度,而其他源距探测器信息反映井眼和地层贡献不同,可组合不同探测器信息来确定地层密度。

The X-ray source is important to achieve“sourceless”nuclear logging,which can avoid radioactive hazards in density measurement.In this paper,the ray generated by 137 Cs source and X-ray source is analyzed in different medium attenuation differences.The Monte Carlo method is used to simulate the energy spectrum and response of different X-ray energy,source distance,formation density and mud cake,and compare the differences between the two sources in the factors such as lithology,density,and borehole environment.The results show that the X-ray energy spectrum is related to the source energy and source distance,a double peak phenomenon will appear because of the backscattering,and will become a single peak as the source distance increases.The X-ray photoelectric effect process is obvious and greatly affected by lithology,and the density sensitivity is greater than 137 Cs;the ultra-near detector counts can calculate the mud cake density,while the other source distance detectors information reflects the borehole and formation contribution.The different detector’s information can be combined to determine the formation density.