Subsurface telemetry in conductive medium for remote sensors [well-logging applications]

For oilfield exploration, a method in which a bullet containing sensors and electronics is ballistically deployed in the earth formation has been propose. The bullet sensors measure formation properties, and data are transmitted back to a host (referred to as "collar") via a wireless channel. In oilfield exploration, a hole, typically 15 to 30 cm in diameter, is drilled to a depth that may extend to a few kilometers. Along with the drill-bit there are many sensors attached to the drill pipe to measure formation properties with a transceiver unit being used for wireless data transfer. In this paper, we present a telemetry system and discuss some theoretical and experimental aspects of signal-to-noise ratio for data transmission.