![]() Therefore the dielectric tools are made as wireline tools. To measure the dielectric properties of the formation, the EM signals generated by the tool must be able to penetrate through the mud layer before reaching the formation, which makes the tool to be designed as a pad-type tool so that it can be mechanically pushed against the borehole wall and reduce the influence from the mud to the tool performance. Due to the high-frequency nature of the dielectric tools, the investigation depth is rather limited (a few inches, see Table 1.2).Īs we know, the borehole mud has high content of water for water-based mud (WBM) and is very lossy to the EM signals, and has high dielectric constant. The dispersion characteristics of the dielectric constant may also be used to identify the formations. It is seen from Chapter 3, Electrical Properties of Sediment Rocks: Mixing Laws and Measurement Methods, that the dielectric constant is not really a constant, it changes with the frequency. Unfortunately, the conventional logging tools such as induction, LWD, and laterolog tools are not sensitive to the dielectric constant change due to the low frequency operation. On the other hand, the conductivities of the fresh water and oil or gas are very similar. It is very natural to use dielectric measurement to identify water versus oil and gas. As discussed in Chapter 3, Electrical Properties of Sediment Rocks: Mixing Laws and Measurement Methods, the dielectric constant of oil and gas are relatively small (1–3) whereas the water has very high dielectric constant (70–81). Therefore, from measurement point of view, higher frequency is preferred when we want to measure the dielectric constant of the formation. When the frequency further increases, the displacement current’s role becomes more important than the conduction current in the EM propagation process. However, when the frequency is getting higher, e.g., in megahertz like in logging-while-drilling (LWD) resistivity frequencies, displacement current will have to be considered, which is determined by the dielectric characteristics of the formation. In Chapter 2, Fundamentals of Electromagnetic Fields Induction Logging Tools and Chapter 3, Electrical Properties of Sediment Rocks: Mixing Laws and Measurement Methods, we noticed that in EM wave propagation, the conductivity is dominant (conduction current) at lower frequencies. In the previous chapters, we discussed electromagnet (EM)-based logging tools working at relatively lower frequencies. Richard Liu, in Theory of Electromagnetic Well Logging, 2017 12.1 Introduction Learn how to transform your electromagnet into a modular characterization system.C. ![]() ![]() The EM-V Series incorporate water-cooled coils and precision yokes made of magnetically soft, ultra-pure steel, assuring precise pole capĪlignment as well as excellent field homogeneity and stability. Choose from 6 repeatable gap widths by unbolting the top plate and clicking the selector into place. The ExactGAP pole gap indexing makes it fast and easy to reconfigure the magnet gap for the required sample or option size without having to re-calibrate the magnet after changing the gap. The EM-V Series electromagnets feature ExactGAP™ indexed pole settings. With true bipolar MPS power output, provides rapid uniform magnetic field ramping and field reversal to avoid discontinuities that occur during zero crossover when using unipolar power supplies. The EM-V series magnet coupled with a Lake Shore magnet power supply (MPS) and teslameter form a versatile laboratory electromagnet capable of producing magnetic fields up to 3.22 T and supporting very fast ramp rates of up to 1 T/s. Including magneto-optical studies, magnetic hysteresis studies, in-line annealing, Hall effect studies, susceptibility measurements, spin magnetic resonance demonstrations, and biological studies. The EM-V Series is ideally suited for integration into customer-designed magnetic test platforms for applications The Lake Shore EM-4V and EM-7V electromagnets (EM-V Series) produce magnetic fields with a variety of indexed air gap and pole cap configurations.
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