随钻核磁共振测井射频线圈优化方法  

Optimization Method of Radio Frequency Coil for Nuclear Magnetic Resonance Logging While Drilling

作　　者：于会媛[1] 王光伟[1] 张嘉伟[1] 张文秀[2] 徐征[3] 徐显能 YU Huiyuan;WANG Guangwei;ZHANG Jiawei;ZHANG Wenxiu;XU Zheng;XU Xianneng(China Oilfield Services LTD., Well-Tech R&D Institute, Beijing 101149, China;Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;School of Electrical Engineering, Chongqing University, Chongqing 400044, China)

机构地区：[1]中海油田服务股份有限公司油田技术研究院,北京101149 [2]中国科学院地质与地球物理研究所,北京100029 [3]重庆大学电气工程学院,重庆400044

出　　处：《测井技术》2020年第6期548-552,共5页Well Logging Technology

基　　金：中国科学院战略性先导科技专项(A类)“深层地质导向技术:随钻核磁共振测井技术”(14020400)。

摘　　要：随钻核磁共振测井是目前最先进的井下油气勘探方法之一,随钻核磁共振探头的性能取决于其主磁体结构和配套的射频线圈。针对Jackson结构的主磁体,为了提高核磁共振信号的信噪比,对配套的螺线管结构射频线圈进行优化。建立射频线圈的解析计算模型,将核磁共振探头等效为螺线线圈与圆柱导体共轴的涡流问题模型,以磁矢量位函数为求解变量,使用分离变量法得到磁场的解析解;以线圈匝数和匝间距为优化变量,以核磁共振信噪比最大化为优化目标,同时考虑到电路的稳定性,以线圈电感为约束条件,对射频线圈的结构进行优化,得到一组高信噪比的射频线圈。Nuclear magnetic resonance logging while drilling(LWD NMR)is one of the most advanced downhole oil and gas exploration methods.The performance of the LWD NMR probe depends on its magnet structure,and the radio frequency(RF)coil.For the main magnet of Jackson structure,in order to improve the signal-to-noise ratio of the NMR signal,this study optimizes the RF coil with solenoid structure.The analytical calculation model of the RF coil is established,the NMR probe is equivalent to the eddy current model of coaxial spiral coil and cylindrical conductor.The magnetic vector potential function is selected as a variable,and the analytical solution of magnetic field is obtained by using the method of separation of variables.The number of turns and distance between turns of the coil are regarded as optimization variables,and the optimization goal was maximization of the signal-to-noise ratio of NMR signal.At the same time,the stability of the circuit was considered,the inductance of the coil is used as the constraint,the optimal RF coil structure with high signal-to-noise ratio is obtained.

关 键 词：随钻核磁共振测井 结构优化 射频线圈 信噪比 

分 类 号：P631.84[天文地球—地质矿产勘探]