核磁共振测井仪探头磁体的优化设计

发布时间：2019-03-03 09:21

【摘要】：核磁共振测井是目前最先进的井下油气勘探方法之一。核磁共振测井原理是通过测井仪探头永磁体对地层施加静磁场，使地层中氢原子核磁化，再利用探头中射频线圈产生射频信号使氢原子核发生共振，最后采集接收共振信号进行成像。国外的核磁共振测井技术研究相对发达，但实施技术保密；国内对核磁共振测井技术研究主要集中在诸如测井解释模型的建立和对岩心地质特性的核磁共振分析等计算机科学及地质学方面。本文重点研究了一种改进型核磁共振测井仪探头磁体系统的设计问题。主要工作如下：首先，基于MAGNET软件分析了国外两种典型核磁共振测井仪探头磁体的静磁场分布，讨论了其产生的探测区域及探测深度两项主要技术指标。在此基础上，提出了一种改进型的探头永磁体设计方案，，结构方案采用了居中式梯度磁场测井方式，磁体结构除了包括还有产生静磁场的主磁体外，还引入了调整磁体，以实现对静磁场的微调。其次，采用表面响应模型与遗传算法相结合的优化策略完成了探头磁体结构的优化设计。依次选取主磁体和调整磁体的几何参数作为优化变量，以提高井眼外探测深度为优化目标，结合拉丁超立方采样策略和多二次径向基函数建立了近似目标函数的表面响应模型，并采用遗传算法对建立的表面响应模型进行寻优，最终实现了探头磁体的最优设计。然后，基于MAGNET软件对优化后的探头磁体产生的静磁场进行了仿真分析，讨论了在井眼四周可能存在的探测区域，以及探测深度和磁场强度的大小，分析了所提出的磁体结构对探测深度的改进效果。最后，在确定好探头磁体结构的基础上，根据测井要求完成了与磁体匹配的射频线圈的设计，分析了射频磁场与静磁场的正交性，确定了所提出的探头磁体在井眼外探测区域的位置和体积。
[Abstract]:Nuclear magnetic resonance logging is one of the most advanced downhole oil and gas exploration methods. The principle of nuclear magnetic resonance logging is that the magnetostatic magnetic field is applied to the formation through the permanent magnet of the probe of the logging tool to magnetize the hydrogen nucleus in the formation, and then the radio frequency signal of the radio frequency coil in the probe is used to cause the resonance of the hydrogen nucleus. Finally, the received resonance signal is collected for imaging. The research of nuclear magnetic resonance logging technology abroad is relatively developed, but the implementation of technology confidentiality; The research of nuclear magnetic resonance logging technology in our country mainly focuses on computer science and geology, such as the establishment of logging interpretation model and the nuclear magnetic resonance analysis of core geological characteristics. This paper focuses on the design of an improved magnetic resonance logging probe magnet system. The main work is as follows: firstly, based on MAGNET software, the static magnetic field distribution of the probe magnet of two kinds of typical nuclear magnetic resonance logging instruments abroad is analyzed, and the detection area and the detection depth of the magnetostatic magnetic field produced by the magnetostatic magnetic field are discussed. On the basis of this, an improved design scheme of probe permanent magnet is presented. The structure of the probe permanent magnet adopts the central gradient magnetic field logging method. The magnet structure not only includes the main magnet which produces static magnetic field, but also introduces the adjusting magnet. In order to achieve the fine-tuning of the static magnetic field. Secondly, the optimization strategy of surface response model and genetic algorithm is used to optimize the structure of probe magnet. The geometry parameters of the main magnet and the adjusted magnet are selected as the optimization variables, and the surface response model of the approximate objective function is established by combining the Latin hypercube sampling strategy and the multi-quadratic radial basis function, in order to improve the detection depth outside the hole. Finally, the optimal design of probe magnet is realized by using genetic algorithm to optimize the established surface response model. Then, the static magnetic field generated by the optimized probe magnet is simulated and analyzed based on MAGNET software, and the possible detection area around the well hole, as well as the detection depth and the magnetic field intensity are discussed, and the static magnetic field generated by the optimized probe magnet is simulated and analyzed. The improvement effect of the proposed magnet structure on the detection depth is analyzed. Finally, on the basis of determining the structure of the probe magnet, the RF coil matching with the magnet is designed according to the logging requirements, and the orthogonality between the RF magnetic field and the static magnetic field is analyzed. The position and volume of the probe magnet outside the well are determined.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.83

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