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

点击翻译按钮获取中文摘要

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.