Method and apparatus for communicating signals from within an encased borehole

摘要

A method and apparatus for communicating signals from within an encased borehole including a wireless communications system for transmitting down-hole environmental data signals between a down-hole tool and a surface receiver. The down-hole tool is disposed within a borehole encased in an electrically conductive casing; the receiver is located at the ground surface. The tool includes a conductive upper and lower tool housing, a plurality of down-hole sensors, and a signal generating device. The sensors and signal generating device are housed within the tool. The generating device receives analog or digital signals of the down-hole environmental conditions from the sensors, converts these signals into a modulation pattern signal which is applied to a carrier signal and conducts a modulated carrier signal into the upper and lower tool housings. An upper contactor or spreader electrically connects the upper housing to a first position on an inside wall of the casing. Similarly, a lower contactor or spreader electrically connects the lower housing to a second position on the inside wall of the casing. The first and second positions are spaced-apart by a pre-determined separation, and define a casing conducting portion therebetween. The transmitted drive signal cause a reciprocating current to flow through the conducting portion thereby inducing a voltage potential on the outside of the well-casing which forms corresponding dipolar electromagnetic field in the earth surrounding the conductive portion and propagating the field upward to be received by the surface receiver.