A new method of wireless data telemetry in oil well services uses compressional acoustic waves to transmit data along the drill string. Coded wave trains are produced by an acoustic transducer, travel through the drill string and are subsequently decoded to recover the data. Normal drilling operations produce in-band acoustic noise at multiple sources at intensities comparable to the transducer output, while propagation through the long drill string further degrades the signal. We describe a theoretical channel model, and, based on this model, demonstrate that a single receiver system has a capacity of several hundred bits per second in such noisy drilling conditions. We analyze a two-receiver scheme that exploits the fact that the dominant noise source and the signal propagate in opposite directions. We show that with two receivers this dominant noise can be cancelled, which results in a significant improvement in capacity over the single receiver.