随钻方位γ能谱测井探测特性的数值模拟研究

Numerical simulation of detecting characteristics of the spectral azimuthal γ-ray logging while drilling

研究仪器探测特性对于前期的仪器结构优选设计及后期的资料解释都有重要意义。首先确定随钻方位γ能谱测井仪的仪器结构,建立相应的MCNP模型,然后仿照感应测井中的几何因子,模拟仪器的径向、纵向、方位积分几何因子;最后模拟研究井眼尺寸、泥浆密度、地层密度、天然放射性物质类型对仪器探测特性的影响。模拟计算结果表明:井眼尺寸、地层密度、天然放射性物质类型对探测特性影响较大,而泥浆密度基本无影响。

[Background]The detection characteristics of the spectral azimuthalγ-ray(SAGR)logging while drilling(LWD)tool are important for the early design of the instrument structure and subsequent interpretation of the logging data,so it is necessary to study its detection characteristics and its influencing factors.[Purpose]This study aims to investigate the effects of wellbore size,mud density,formation density,and natural radioactive material types on the SAGR instrument detection characteristics.[Methods]First of all,the instrument structure of the LWD spectral azimuthal gamma ray tool was determined,then the corresponding MCNP model was established.Based on the geometric factors in the induction logging,the radial,longitudinal and circumferential integral geometry factors of the SAGR instrument were simulated.Finally,the influence of wellbore size,mud density,formation density and different natural radioactive materials on the detection characteristics of the SAGR were studied by simulation.[Results]The results show that the wellbore size,formation density and natural radioactive material types have a great influence on the SAGR detection characteristics,while the mud density have no effect.[Conclusion]This study provides a theoretical reference for instrument design and logging data interpretation of the spectral azimuthalγ-ray logging while drilling tool.