【摘要】 随钻核磁共振是将核磁共振装置精巧设计在钻杆上,在钻头快速钻进的条件下实现核磁共振测量，具有广阔应用前景，是核磁共振科学仪器研制的前沿领域.随钻核磁共振仪器的射频线圈是仪器跟随钻头在水平井快速钻进时产生射频磁场激励样品并接收核磁共振信号的关键组件.射频线圈的性能极大程度上决定着仪器的探测特性，对于仪器的设计与优化，高信噪比、低功耗是高品质随钻核磁共振仪器线圈的设计目标.对应着线圈的电性参数中的高发射效率、低线圈电阻和线圈品质因数.在以往的射频线圈设计方法中，这些参数的优化通常相互制约，优化耗时长且依赖于线圈设计经验，传统的正演线圈设计思路难以获得理论最佳结果.本文采用逆向设计思路，选择目标场法进行随钻核磁共振探头射频线圈设计.通过建立螺线管线圈电流与射频磁场之间的关系，设置线圈电感为约束条件，以最大化探头信噪比为目标，采用正则化方法求解目标函数以获取流函数，进而确定线圈绕线结构.同时，结合研究团队自研的随钻核磁共振仪器的静磁场分布，构建理想目标射频磁场分布并进行逆向求解以获取线圈结构.研究团队对已有的等间距线圈和本方法设计的新线圈开展实验验证，结果显示新线圈测得的信号幅度增加12%，信噪比提高9%.基于逆向设计思路的目标场法可有效优化随钻核磁共振线圈性能，解决了传统设计中参数优化缓慢的问题，为随钻核磁共振线圈的高效设计与优化提供了可行方法，有助于提升仪器探测特性.更多还原

【Abstract】 Logging While Drilling Nuclear Magnetic Resonance(LWD NMR) integrates a precision-engineered NMR device within the drill string, enabling NMR measurements under conditions of rapid drill bit penetration.This technique holds significant application potential and represents a cutting-edge field in the development of NMR scientific instruments. The radiofrequency(RF) coil of the LWD NMR probe is a key component,generating radiofrequency magnetic fields to excite samples and receive NMR signals as the instrument accompanies the bit during rapid horizontal drilling. The RF coil’s performance directly influences the detection characteristics of the NMR instrument, making it essential to design coils with high Signal-to-Noise Ratios(SNR) and low power consumption. An ideal RF coil should exhibit performance characterized by high SNR,high transmission efficiency, and low power consumption. However, optimizing these key parameters is often mutually constrained. Traditional coil design approaches generally rely on empirical methods and structural forward modeling of the coil for parameter optimization, which often restricts the achievement of optimal results.This paper proposes a novel inverse design approach for the RF coil of LWD NMR probes, extending the target field method to RF coil design for downhole tools. It establishes a relationship between the current in the solenoidal coil and the RF magnetic field outside the coil, while setting coil inductance as a constraint. The objective is to maximize the probe’s SNR, utilizing regularization techniques to solve the objective function. The coil’s winding pattern is determined using the stream function. This paper constructs the target RF field distribution based on the static magnetic field generated by the magnet of the LWD NMR probe developed by the research team. The optimal RF field is inversely solved to determine the coil structure. Experimental validation was conducted using conventional solenoidal coils and the newly designed coil. The research team performed experimental verification on existing equidistant coils and the new coil designed via this method. Results show that the signal amplitude measured with the new coil increased by 12%, and the SNR improved by 9%. The target field method based on the inverse design approach can effectively optimize the performance of LWD NMR coils, address the slow parameter optimization issue in traditional designs, offer a viable method for the efficient design and optimization of LWD NMR coils, and aid in enhancing the probe’s detection performance.更多还原