So-called polarization horns appear in electromagnetic well logs when the sondes move through the interface between formations of different conductivities. Since the early 1990s, peaks in the logs have been attributed to the influence of surface charges due to the presence of electric field components perpendicular to the interfaces. A new analysis finds that surface charges should not be pinpointed as the immediate cause for the appearance of interface peaks in electromagnetic logs from any tool operating in any frequency range. This is accomplished by calculating the derivatives of the magnetic field components with respect to the sonde’s vertical position as it crosses the interface between two homogeneous isotropic media. The mathematical expressions reveal the components with smooth transitions and the ones with discontinuities in their rates of change across the interface. The analysis is applied to the four components needed to simulate the responses of coaxial and coplanar coil configurations in dipping logs. The results show that only the horizontal field from a horizontal dipole source suffers an influence from the current density field perpendicular to the interface between the two media, which gives rise to surface charges, but even for this component, the nonsmooth transitions are not associated with the perpendicular current. An anisotropic example gives further support to the conclusion that the polarization horns are associated with the discontinuous current density field parallel to the interface rather than with the continuous current across the interface.

中文翻译：

---

电磁测井中“极化”角的原因新探

当探测器通过不同电导率的地层之间的界面移动时，电磁测井中就会出现所谓的极化角。自1990年代初以来，由于垂直于界面的电场成分的存在，测井的峰值已归因于表面电荷的影响。一项新的分析发现，不应将表面电荷确定为在任何频率范围内运行的任何工具产生的电磁测井曲线中界面峰出现的直接原因。这是通过计算当磁场穿过两个均匀各向同性介质之间的界面时，相对于探空仪垂直位置的磁场分量的导数来实现的。数学表达式揭示了具有平滑过渡的组件以及跨界面变化率不连续的组件。该分析适用于在浸渍测井中模拟同轴和共面线圈配置响应所需的四个组件。结果表明，仅来自水平偶极子源的水平场受到垂直于两种介质之间界面的电流密度场的影响，这会产生表面电荷，但是即使对于该分量，非光滑跃迁也不会与垂直电流。一个各向异性的例子进一步支持了以下结论：该分析适用于在浸渍测井中模拟同轴和共面线圈配置响应所需的四个组件。结果表明，仅来自水平偶极子源的水平场受到垂直于两种介质之间界面的电流密度场的影响，这会产生表面电荷，但是即使对于该分量，非光滑跃迁也不会与垂直电流。一个各向异性的例子进一步支持了以下结论：该分析适用于在浸渍测井中模拟同轴和共面线圈配置响应所需的四个组件。结果表明，仅来自水平偶极子源的水平场受到垂直于两种介质之间界面的电流密度场的影响，这会产生表面电荷，但是即使对于该分量，非光滑跃迁也不会与垂直电流。一个各向异性的例子进一步支持了以下结论：非平滑过渡与垂直电流无关。一个各向异性的例子进一步支持了以下结论：非平滑过渡与垂直电流无关。一个各向异性的例子进一步支持了以下结论：极化角与平行于界面的不连续电流密度场有关，而不是与穿过界面的连续电流有关。