电缆核磁共振测井仪探测特性研究

Investigation Characteristics of NMR Wireline Logging Tools

磁场形状和分布对核磁共振测井仪探测特性有决定性的作用.该文利用电磁场有限元方法,模拟分析了国际主流核磁共振测井仪MRIL-P、CMR、MREx、以及MR Scanner等4种仪器的磁场分布,考察了探头结构参数对磁场分布的影响,并进一步分析了仪器探测特性及其影响因素,同时对探头磁场形状进行了优化匹配,确定了探头的结构设计,并对比分析了4种探头之间的优缺点.结果表明,梯度磁场方案优于均匀磁场方案;居中型探头结构相对简单,信号量大,但其测量信号受钻井液影响;贴井壁型探头结构相对复杂,信号量较小,但其设计灵活,测量信号不受钻井液影响.

The magnetic field shape is critical to the performance of Nuclear Magnetic Resonance Well Logging tools.In order to understand and re-construct the investigation characteristics of four international leading NMR tools,MRIL-P,CMR,MREx,and MR Scanner,their field distribution is simulated by Finite Elements Method（FEM）.The influence of sensor configurations on field distribution is analyzed,and then sensor performance and influence factors are investigated.The results indicated that inhomogeneous field configurations are better than homogeneous field ones.Centric sensors have relatively simple geometries and high signal intensity,however,their measurements are sensitive to the mud,while eccentric ones have complicate geometries,low signal intensity,but they have various configurations and no restriction for mud type and salinity.