Patent ID: 8800684

Claim:
A method of forming boreholes in an earth formation, the method comprising: drilling a reference borehole in the earth formation; transmitting a first signal into the earth formation from a transmitter at a known location in the reference borehole; receiving signals at at least three spaced sensors positioned at selected locations responsive to the transmitted first signal; estimating a signal velocity in the earth formation utilizing the signals received at the at least three sensors responsive to the transmitted first signal; drilling at least one other borehole in the earth formation; transmitting a second signal into the earth formation from a transmitter in the at least one other borehole; receiving signals at the at least three sensors responsive to the transmitted second signal; and estimating a path of the at least one other borehole utilizing the signals received by the at least three sensors responsive to the transmitted second signal and the estimated signal velocity in the earth formation.