Electromagnetic Modeling of Transmissions through an In Situ Gasified Coal Seam

As an aid in the design of an electromagnetic system for the measurement of the overall width of the gasified section of an underground (in situ) coal gasification process, an analytical model has been developed that will predict the electromagnetic field transmitted through the gasified portion of the coal seam. The gasified and ambient (ungasified) coal media have been modeled electrically as being lossy, surrounded above and below by relatively high-conducting overburden and underburden. Vertical electric and horizontal magnetic dipoles have been investigated utilizing a geometrical optics formulation. Indications from the frequency responses of the transmission monitoring scheme are that the system is capable of measuring the width of the in situ gasification process with reasonable accuracy.