With the development of geophysical exploration technology, the demand for accuracy and quality of seismic data acquisition becomes higher 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, 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. It is the key part of the entire seismic data acquisition. Geophone can be classified 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.

Basic Structure and Working Principle of Geophone

Geophone can be divided into 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.

About Geophone Magnet

As the core component of the product, geophone magnet is 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 magnet. Air gap flux will be influenced by magnetic after effect, temperature, electromagnetic interference and vibration, therefore cause the geophone parameter’s change. Actually, AlNiCo magnet, sintered Samarium Cobalt magnet, and sintered Neodymium magnet was all applied into geophone, but cast AlNiCo magnet is still regarded as the optimum selection of geophone magnet due to its high accuracy, stability and cost-effective. It also should be noted that the dimension tolerance of geophone magnet is very tight.