Patent ID: 8393412

Claim:
A sonic telemetry system for determining the positional profile of a subsurface well including a bottom hole assembly (BHA) and formed with a drill including a drill bit, which system comprises: multiple surface sonic transmitters positioned along an intended path of a well located within a known soil formation; a sonic downhole transceiver positioned in proximity to the BHA, said sonic downhole transceiver being adapted for receiving signals from the surface sonic transmitters and transmitting a telemetered data stream from the drill; a surface receiving device adapted for receiving said telemetered data stream; said telemetered data stream comprising relative time of flight (TOF) information retrieved from signals sent by said surface transmitters and received by said sonic downhole transceiver; a processor connected to said surface receiving device and programmed to compare said TOF information with actual transmission times and the surface locations of the transmitting transmitters; said processor being adapted for calculating the position of the sonic downhole transceiver relative to said sonic transmitters during a drilling operation based on the TOF and the time of transmission data collection; wherein said processor for comparing TOF is adapted to include correlation properties of a pseudo noise code directly modulated on the sonic carrier using standard digital modulation methods to determine the TOF at a resolution sufficient to achieve a one meter or better ranging accuracy; said pseudo noise code bits are modulated onto linear frequency chirps then transmitted at a rate below the directly modulated code; said linear frequency chirps used to improve correlation properties of the pseudo noise code, whereby said correlation property improvements result in a reduced receiver bandwidth with equal ranging accuracy; and said surface sonic transmitters further comprise an extensional wave sonic source and an interface at which extensional bar waves are converted to pressure waves (P-waves) in the subsurface formation.