Development of a Downhole Tri-axial magnetic field measuring system and its application to Subsurface Fracture Characterization

本课题分三个阶段展开：(1)井下三轴磁场测量系统的硬件开发。该系统的基础是日本MITT下属的NEDO开发的井下工具。为了了解该仪器的特性，在位于东八里曼台地热田的东北大学实验场进行了空气和钻孔的基础实验。计算了工具的理论响应，考察了周围材料对电导率的方向性。(2)实验显示了同相和方相分量的独立响应。对电导率和磁导率同时测井方法进行了理论探讨。利用低频井下仪器对井间层析成像技术进行了测试。该系统使用2 MHz-32 MHz，这是常规井下雷达和感应技术的中频。通过这个项目，我们从实验和理论上证明了井下三轴磁场测量系统可以同时用于电导率和磁导率的测井，并可用于地下裂缝分类表征。

This project was carried out in the three phases described below.(1) Hardware development of the downhole tri-axial magnetic field measuring system was carried out. The basis of the system is the downhole tool developed by the NEDO under MITT, Japan. Fundamental experiment in air and in a borehole at Tohoku University experiment site at Higashi Hachimantai Geothermal field was achieved for understanding the tool characteristics. Theoretical tool response was calculated and directivity to electrical conductivity of the surround material was examined.(2) Independent response of in-phase and quadrate - phase components was experimentally shown. Theoretical approach to the method of simultaneous electrical conductivity and magnetic permeability logging was studied. Also, we found this technique is sensitive to the thin layer detection and precise determination of geological boundary.(3) A Cross-hole tomography technique was tested by using a low frequency downhole tool. The system use 2MHz-32MHz, which are intermediate frequency of conventional borehole radar and induction technique. We could show that this technique can be used in relatively conducting material.Throughout this project, we showed experimentally and theoretically that the dowohole tri-axial magnetic field measuring system can be used for simultaneous electrical conductivity ad magnetic permeability logging, and that it is useful for characterization of subsurface fracture classification.