Logging while drilling system signal recovery system

Abstract From the Canadian patent

Data signals indicative of subsurface well physical measurements and t or geophysical measurements are transmitted through the drilling mud by pressure pulsations originating at a downhole apparatus. Two closely spaced pressure sensors measure mud pressure pulsations in a mud line at a surface location. Both of the measured pressure pulsation signals are time shifted an amount equal to the travel time of the upwardly and downwardly propagation acoustic velocity in the mud between the two pressure sensors by separate time delay circuits. Summing circuits separately combine the original and delayed signals to cancel the respective upwardly and downwardly propagating energy from the two …