随钻核磁共振测井静磁场温度特性仿真研究

Simulation Study on Temperature Characteristics of Static Magnetic Field for NMR logging While Drilling

为探究随钻核磁共振测井探头中目标区域静磁场的温度特性,在现有磁体系统结构基础上,首先利用有限元仿真分析了磁体系统中各个材料对静磁场的影响,然后分别利用有限元仿真和实测得到了不同温度下同一探测点的静磁场变化规律,且有限元仿真结果和实测结果比较吻合。通过有限元仿真分析了不同温度下的核磁共振有效区域分布,分别讨论了核磁共振射频场中心频率不变和可变2种情况下有效区域的分布情况,在保证有效区域位置不变的前提下,重点分析了对应射频场中心频率的调整策略。结果表明,所建立的随钻核磁共振测井静磁场有限元仿真模型可以方便有效地给出射频场中心频率随温度的调整策略,为探头的优化设计与工程应用提供数据参考,具有实际指导作用。

In order to explore the temperature characteristics of the static magnetic field in the target area of the nuclear magnetic resonance(NMR)logging while drilling probe,based on the existing magnet system,firstly,the influence of each material in the magnet system on the static magnetic field is analyzed by simulation.The finite element simulation and measurement are utilized to obtain the static magnetic field variation of the same detection point at different temperatures,and the finite element simulation results are in good agreement with the measured results.The distribution of the effective area of NMR at different temperatures is analyzed through simulation.The distribution of the effective area is discussed under the two conditions of the center frequency of the NMR radio frequency field being constant and variable.Under the premise of keeping the effective area position unchanged,the focus is on the adjustment strategy of the corresponding radio frequency field center frequency.The results show that the static magnetic field simulation model of NMR logging while drilling can conveniently and effectively give the adjustment strategy of the center frequency for the radio frequency field with the temperature,and provide data reference for the optimization design and engineering application of the probe,which have practical guidance.