Method and system for seismic continuous bit positioning

Claim 3

The method according to claim 1 wherein the acoustic signal generated by the continuous rotation of said drill bit against the formation is segregated from other acoustic signals by the steps of selecting assumed positions for said drill bit, time shifting the acoustic signals detected by said seismic detectors, correlating the time shifted acoustic signals and comparing the coherency values.

Claim 4

The method according to claim 1 wherein the steps of time shifting the acoustic signals, correlating the time shifted acoustic signals and comparing the coherency values are carried out by a computer at the well site in real time.

Claim 5

The method according to claim 1 wherein the acoustic signal generated by the drill bit is coherent and has a continuous waveform.

Claim 6

The method according to claim 1 wherein the acoustic signal generated by the drill bit may be varied by varying the rotational speed of said drill bit.

Claim 7

The method according to claim 1 wherein the steps of selecting assumed positions for said drill bit, time shifting the acoustic signals, correlating the time shifted acoustic signals and comparing the coherency values are performed at discrete intervals at the well site in real time.

Claim 8

The method according to claim 1 wherein the steps of selecting assumed positions for said drill bit, time shifting the acoustic signals, correlating the time shifted acoustic signals and comparing the coherency values are performed continuously at the well site in real time.

Claim 9

The method according to claim 1 wherein the step of correlating the time shifted acoustic signals is performed by adding and/or multiplying the amplitude values of the time shifted acoustic signals.

Claim 11

The method according to claim 1 wherein said drill bit is rotated by a drilling rig including a drill string and the depth of said drill bit in the borehole is estimated as a function of the known length of the drill string.

Claim 12

The method according to claim 1 wherein the depth of said drill bit in the borehole is determined as a function of the known depth of geologic boundaries.

Claim 13

The method according to claim 1 wherein said seismic detectors are spaced apart in a two-dimensional array.

Claim 14

The method according to claim 12 wherein said array of seismic detectors includes at least three seismic detectors.

Claim 15

The method according to claim 1 further comprising the step of recording the acoustic signals detected at each seismic detector.

Claim 16

In a drill bit location system for a rotary drilling rig, said rotary drilling rig including a drill string and a drilling mechanism to rotate said drill string and an associated rotatable drill bit to drill a borehole, said drill bit location system including an array of spaced seismic detectors to detect seismic signals and signal processing means coupled to said seismic detectors for processing the seismic signals, a method for locating the position of said rotatable drill bit in the earth during continuous rotation of said rotatable drill bit in the borehole, said method comprising the steps of: detecting a drill bit acoustic signal emanating from said rotatable drill bit during continuous rotation of said rotatable drill bit against the formation being drilled, the drill bit acoustic signal being detected by said array of seismic detectors; positioning said array of seismic detectors to obtain phase differences in the drill bit acoustic signal detected at different seismic detector positions; determining a set of assumed positions for said rotatable drill bit utilizing known information about the approximate depth of said drill bit; calculating the travel times for the drill bit acoustic signal from one of the assumed positions for said rotatable drill bit to each of said seismic detectors in said array of seismic detectors; segregating the drill bit acoustic signal from other acoustic signals detected by said seismic detectors by (1) time shifting the acoustic signal detected by each of said seismic detectors relative to a time reference by an amount corresponding to the calculated travel time of the drill bit acoustic signal from said one assumed position to said seismic detector and (2) correlating the time shifted acoustic signals for said one assumed position of said rotatable drill bit by calculating a coherency value representing the coherency of the time shifted acoustic signals; repeating the steps of calculating travel times of the drill bit acoustic signal and segregating the drill bit acoustic signal from other acoustic signals for each assumed position for said rotatable drill bit; and comparing the coherency values for all assumed positions for said rotatable drill bit to determine the location of said rotatable drill bit.

Claim 17

In a drill bit location system for a rotary drilling rig, said rotary drilling rig including a drill string and a drilling mechanism to rotate said drill string and an associated rotatable drill bit to drill a borehole, said drill bit location system including an array of spaced seismic detectors to detect seismic signals and signal processing means coupled to said seismic detectors for processing the seismic signals, a method for locating the position of said rotatable drill bit in the earth during continuous rotation of said rotatable drill bit in the borehole, said method comprising the steps of: detecting a drill bit acoustic signal emanating from said rotatable drill bit during continuous rotation of said rotatable drill bit against the formation being drilled, the drill bit acoustic signal being detected by said array of seismic detectors; positioning said array of seismic detectors to obtain phase differences in the drill bit acoustic signal detected at different seismic detector positions; determining a set of assumed positions for said rotatable drill bit utilizing known information about the approximate depth of said drill bit; calculating the travel times for the drill bit acoustic signal from one of the assumed positions for said rotatable drill bit to each of said seismic detectors in said array of seismic detectors; segregating the drill bit acoustic signal from other acoustic signals detected by said seismic detectors by (1) time shifting the acoustic signal detected by each of said seismic detectors relative to a time reference by an amount corresponding to the calculated travel time of the drill bit acoustic signal from said one assumed position to said seismic detector and (2) correlating the time shifted acoustic signals for said one assumed position of said rotatable drill bit by calculating a coherency value representing the coherency of the time shifted acoustic signals; repeating the steps of calculating travel times of the drill bit acoustic signal and segregating the drill bit acoustic signal from other acoustic signals for each assumed position for said rotatable drill bit; and comparing the coherency values for all assumed positions for said rotatable drill bit to determine the location of said rotatable drill bit.

Claim 18

The method according to claim 15 wherein the step of segregating the drill bit acoustic signal from other acoustic signals is carried out by a computer at the well site in real time.

Claim 19

The method according to claim 15 wherein the drill bit acoustic signal is coherent and has a continuous waveform.

Claim 20

The method according to claim 15 wherein the drill bit acoustic signal may be varied by varying the rotational speed of said rotatable drill bit.

Claim 21

The method according to claim 15 wherein the steps of determining assumed positions for said rotatable drill bit, calculating travel times, segregating the drill bit acoustic signal from other acoustic signals and comparing coherency values are performed at discrete intervals at the well site in real time.

Claim 22

The method according to claim 15 wherein the steps of determining positions for said rotatable drill bit, calculating travel times, segregating the drill bit acoustic signal from other acoustic signals and comparing coherency values are performed continuously at the well site in real time.

Claim 23

The method according to claim 15 wherein correlation of the time shifted acoustic signals is performed by adding and/or multiplying the amplitude values of the time shifted acoustic signals.

Claim 25

The method according to claim 15 wherein the approximate depth of said drill bit in the borehole is a function of the known length of the drill string.

Claim 26

The method according to claim 15 wherein the approximate depth of said rotatable drill bit in the borehole is a function of the known depth of geologic boundaries.

Claim 29

The method according to claim 25 wherein the step of segregating the drill bit acoustic signal from other acoustic signals is carried out by a computer at the well site in real time.

Claim 30

The method according to claim 25 wherein the step of correlating the adjusted acoustic signals is performed by adding and/or multiplying the amplitude values of the adjusted acoustic signals.

Claim 31

The method according to claim 25 wherein the step of adjusting the time reference of the acoustic signals is performed by time shifting the acoustic signals by an amount corresponding to the calculated travel times.

Claim 32

The method according to claim 25 wherein the location of said drill bit corresponds to the highest coherency value of the set of coherency values.

Claim 33

The method according to claim 25 wherein said drill bit is rotated by a drilling rig including a drilling string and the depth of said drill bit in the borehole is estimated as a function of the known length of the drill string.