Geophone Magnets

With the development of geophysical exploration technology, the accuracy and quality demands of seismic data acquisition are much greater than before. The data need to have broadband, high-fidelity, high signal-to-noise ratio, and high dynamic to identify lithology, fluid, and fractured reservoir, thus improve reservoir location, characteristics, connectivity, and ultimately enhance oil recovery. Geophone is kind of professional sensor which converts surface mechanical vibration to the electric signal, or an electromechanical converter for converting mechanical energy to electric energy. Geophone is the key part of the entire seismic data acquisition. Geophone can be divided into electromagnetic induction type, the piezoelectric ceramic type, MEMS type, and fiber optics type according to their working principles. Electric induction type is the most commonly used among them and moving coil geophone is the most representative one.

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Structure and Working Principle of Geophone

Geophone can be classified to vibration system and magnetic circuit system. The shell is fabricated by cylinder-shape soft iron, and midsection is magnetic circuit system. Magnetic circuit system contains magnet and two pole shoes which fixed on the shell. The space between the soft iron shell and geophone magnet is vibration system which includes coil, coil support and springs, and these parts formed a coasting body. Insert geophone vertically into the surface, then geophone will couple with land via the tail cone of the shell. Surface vibration will cause relative motion between coasting body and shell, that is, coil had a relative motion in the magnetic field, hence output current signal corresponding to the vibration period. The structure of underground strata will be indicated after signal processing.

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About Geophone Magnets

As the core component of the product, geophone magnets are not only influenced main indices and parameters of geophone, but also affected its cost. Different type of permanent magnet will offer different feature to geophone. The air gap flux is only determined by parameters of geophone magnets. Air gap flux will be influenced by magnetic after effect, temperature, electromagnetic interference, and vibration, therefore cause the geophone parameter’s change. AlNiCo magnets, Samarium Cobalt magnets and Neodymium magnets were all applied into geophone, but AlNiCo magnets are still regarded as the optimum selection of geophone magnets due to its high accuracy, stability and cost-effective. It also should be noted that the dimension tolerance of geophone magnets is very tight.

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