Magnetic susceptibility registration in ICDP boreholes - test of a new logging tool

磁化率是岩石最常用的物理性质之一。在岩心或钻孔中记录该参数可支持岩性剖面的构建和钻孔之间的对比。记录磁化率的仪器通常使用固定的场振幅来构造所施加的交流磁场。然而，在最近的工作中已经表明，磁化率的重要亚铁磁性矿物磁黄铁矿和钛磁铁矿强烈依赖于交流场的振幅。这对磁化率测井的解释和对比具有重要意义。GFZ-OSG公司新研制的小井眼磁化率测井仪MS 2 H是第一台考虑场相关性影响的磁化率测井仪。在这个项目的框架内，我们计划测试新的探头在ICDP钻孔中的应用。初步的案例研究表明，依赖于磁场的磁化率测量可以提供有关熔岩流成分变化的信息，并可能使磁铁矿和磁黄铁矿的岩石被磁化。这种测试的结果被认为是有效解释磁化率测井的关键。

Magnetic susceptibility is one of the most commonly measured rock physical property. The logging of this parameter on drillcores or in boreholes supports the construction of lithological profiles and correlation between drilling holes. Instruments, recording the magnetic susceptibility are commonly constructed using a fixed field amplitude for the applied ac magnetic field. However, as has been shown in recent work, the susceptibility of important ferrimagnetic minerals as pyrrhotite and titanomagnetite strongly depends on the ac-field amplitude. This has important implications for the interpretation and correlation of susceptibility logs. The newly developed slim-hole sonde MS2H of GFZ-OSG is the first susceptibility logging tool that considers the effect of field dependency. In the framework of this project we plan to test the application of the new sonde in ICDP drillholes. Preliminary case studies have shown that field dependent susceptibility measurements can provide information concering variations in the composition of lava flows and may enable magnetite and pyrrhotite-bearing rocks to be distinguised. The results of such tests are considered to be critical for the effective interpretation of susceptibility logs.