Apparatus and method for aligning downhole measurements

Abstract

Apparatuses and methods are described, such as for aligning downhole measurements. Apparatuses and methods include an arrangement of at least two tilted transmitters and at least one tilted receiver along a longitudinal axis of the tool. A first and second plurality of azimuthal measurements are processed to provide a first and a second plurality of higher order mode signals configured to be time-shifted.

1 . A method of aligning a plurality of downhole electromagnetic measurements, comprising:
 activating, at an initial recording time, a first transmitter antenna in an arrangement along a longitudinal axis, the first transmitter antenna activated at an operating frequency;   activating, at the initial recording time, a second transmitter antenna in the arrangement, the second transmitter antenna disposed longitudinally from the first transmitter antenna along the longitudinal axis, the second transmitter antenna activated at substantially the same operating frequency as the first transmitter antenna;   collecting at a first receiver antenna a first plurality of azimuthal measurements associated with the first transmitter antenna;   collecting at a second receiver antenna a second plurality of azimuthal measurements associated with the second transmitter antenna;   processing the first plurality of azimuthal measurements to produce a corresponding first plurality of higher order mode signals;   processing the second plurality of azimuthal measurements to produce a corresponding second plurality of higher order mode signals; and   aligning the first plurality of higher order mode signals and the second plurality of higher order mode signals in the time-domain by a time-shift.   
     
     
         2 . The method of  claim 1 , wherein the first and second transmitter antennas are separated by the first and second receiver antennas and arranged along the longitudinal axis of a tool with the first transmitter antenna, the second transmitter antenna, the first receiver antenna, and the second receiver antenna having a non-zero angle with respect to the longitudinal axis. 
     
     
         3 . The method of  claim 2 , wherein a first longitudinal distance from the first transmitter antenna to the first receiver antenna is substantially equal to a second longitudinal distance from the second transmitter antenna to the second receiver antenna. 
     
     
         4 . The method of  claim 3 , wherein the operating frequency is selected according to the first or second longitudinal distance. 
     
     
         5 . The method of  claim 1 , wherein:
 the first transmitter antenna and the first receiver antenna are spaced approximately equidistant from a first reference point, wherein the first plurality of higher order mode signals is associated with the first reference point; and   the second transmitter antenna and the second receiver antenna are spaced approximately equidistant from a second reference point, wherein the second plurality of higher order mode signals is associated with the second reference point.   
     
     
         6 . The method of  claim 1 , wherein the first and second plurality of azimuthal measurements are collected over a predetermined time interval. 
     
     
         7 . The method of  claim 1 , wherein the aligning further comprises:
 identifying a similarity as an identified similarity between the first plurality of higher order mode signals and the second plurality of higher order mode signals; and   time-shifting the first or second plurality of higher order mode signals such that the identified similarity corresponds to the time-domain of either the first plurality of higher order mode signals or the second plurality of higher order mode signals.   
     
     
         8 . The method of  claim 1 , wherein the aligning further comprises:
 determining a common parameter, including at least one of a slope, a peak, or a sample variance, of at least a portion of the first plurality of higher order mode signals and at least a portion of the second plurality of higher order mode signals; and   correlating the portion of the first plurality of higher order mode signals and the portion of the second plurality of higher order mode signals in the time-domain based on the common parameter.   
     
     
         9 . The method of  claim 1 , further comprising:
 obtaining, at a drill bit, a drill bit depth measurement at approximately the initial recording time.   
     
     
         10 . The method of  claim 9 , further comprising obtaining the drill bit depth measurement over the predetermined time interval. 
     
     
         11 . The method of  claim 9 , wherein a longitudinal distance between the drill bit and at least one of the first or second reference points is predetermined. 
     
     
         12 . The method of  claim 9 , further comprising:
 correlating a depth of at least one of the first or second reference points with the drill bit depth measurement.   
     
     
         13 . The method of  claim 5 , further comprising:
 correlating the time-shift to a distance between the first and second reference points so as to determine a velocity of the tool.   
     
     
         14 . A method of aligning a plurality of downhole electromagnetic measurements, comprising:
 activating, at an initial recording time and an operating frequency, a first transmitter antenna in an arrangement along a longitudinal axis, the first transmitter antenna tilted with respect to the longitudinal axis;   activating, at the initial recording time and a substantially similar operating frequency, a second transmitter antenna in the arrangement, the second transmitter antenna disposed longitudinally from the first transmitter antenna along the longitudinal axis, the second transmitter antenna tilted with respect to the longitudinal axis;   collecting, at a receiver antenna, a first plurality of azimuthal measurements associated with the first transmitter antenna, and a second plurality of azimuthal measurements associated with the second transmitter antenna, wherein the first plurality of azimuthal measurements and the second plurality of azimuthal measurements are offset from each other in the time-domain, wherein the receiver antenna is located between the first and second transmitter antennas, the receiver antenna tilted with respect to the longitudinal axis;   processing the first plurality of azimuthal measurements to produce a corresponding first plurality of higher order mode signals;   processing the second plurality of azimuthal measurements to produce a corresponding second plurality of higher order mode signals; and   aligning the first plurality of higher order mode signals and the second plurality of higher order mode signals in the time-domain.   
     
     
         15 . The method of  claim 14 , wherein the arrangement includes the first and second transmitter antennas separated by the receiver antenna, wherein a first longitudinal distance from the first transmitter antenna to the receiver antenna is substantially equal to a second longitudinal distance from the second transmitter antenna to the receiver antenna, such that the receiver antenna is located at a longitudinal center point. 
     
     
         16 . The method of  claim 15 , wherein the operating frequency is selected according to the first or second longitudinal distance. 
     
     
         17 . The method of  claim 14 , wherein:
 the first transmitter antenna and the receiver antenna are spaced approximately equidistant from a first reference point, wherein the first plurality of higher order mode signals is associated with the first reference point; and   the second transmitter antenna and the receiver antenna are spaced approximately equidistant from a second reference point, wherein the second plurality of higher order mode signals is associated with the second reference point.   
     
     
         18 . The method of  claim 14 , wherein the first and second plurality of azimuthal measurements are collected over a predetermined time interval. 
     
     
         19 . The method of  claim 14 , wherein the aligning further comprises:
 identifying a similarity as an identified similarity between the first plurality of higher order mode signals and the second plurality of higher order mode signals; and   time-shifting the first or second plurality of higher order mode signals such that the identified similarity of the first and the second plurality of higher order mode signals corresponds in the time-domain of either the first plurality of higher order mode signals or the second plurality of higher order mode signals.   
     
     
         20 . The method of  claim 14 , wherein the aligning further comprises:
 determining a common parameter, including at least one of a slope, a peak, or a sample variance, of at least a portion of the first plurality of higher order mode signals and at least a portion of the second plurality of higher order mode signals; and   correlating the portion of the first plurality of higher order mode signals and the portion of the second plurality of higher order mode signals in the time-domain based on the common parameter.   
     
     
         21 . The method of  claim 14 , further comprising:
 obtaining, at a drill bit, a drill bit depth measurement at approximately the initial recording time.   
     
     
         22 . The method of  claim 21 , further comprising:
 obtaining the drill bit depth measurement over the predetermined time interval.   
     
     
         23 . The method of  claim 17 , wherein a longitudinal distance between the drill bit and at least one of the first or second reference points is known. 
     
     
         24 . The method of  claim 23 , further comprising:
 correlating the depth of at least one of the first or second reference points with the drill bit depth.   
     
     
         25 . The method of  claim 17 , further comprising:
 correlating the time-shift to a distance between the first and second reference points so as to determine a velocity of a tool.   
     
     
         26 . The method of  claim 14 , further comprising:
 processing the aligned first and second plurality of higher order mode signals to provide a formation resistivity measurement.   
     
     
         27 . The method of  claim 14 , wherein the method is conducted during a logging-while-drilling operation. 
     
     
         28 . A machine-readable storage medium having instructions stored thereon, which, when, performed by a machine, cause the machine to perform the method of  claim 14 . 
     
     
         29 . An apparatus to align a plurality of downhole electromagnetic measurements, comprising:
 a tool having an arrangement of transmitter antennas and receiver antennas, each transmitter antenna configured to operate at a substantially similar operating frequency, along a longitudinal axis of the tool, the tool including:
 a first and a second tilted transmitter antenna, the first tilted transmitter antenna disposed longitudinally above the second tilted transmitter antenna; 
 a first tilted receiver antenna disposed a predetermined first distance from the first tilted transmitter antenna, the first tilted transmitter antenna and the first tilted receiver antenna spaced approximately equidistant from a first reference point; and 
 a second tilted receiver antenna disposed a predetermined second distance from the second tilted transmitter antenna, the second tilted transmitter antenna and the second tilted receiver antenna spaced approximately equidistant from a second reference point, wherein the first and second reference points are disposed a predetermined third distance from each other; 
   a drill bit, including a depth measurement device, wherein the depth measurement device is located at a fourth distance from at least one of the first or second reference points; and   a processing unit configured to control activation of the transmitter antennas and the receiver antennas and to process a first plurality of electromagnetic measurements associated with the first reference point and a second plurality of electromagnetic measurements associated with the second reference point.   
     
     
         30 . An apparatus to align a plurality of downhole electromagnetic measurements, comprising:
 a first transmitter antenna located along a longitudinal axis of a tool, the first transmitter antenna configured to operate at a first operating frequency, the first transmitter antenna tilted with respect to the longitudinal axis;   a second transmitter antenna located along the longitudinal axis of the tool, the second transmitter antenna configured to operate at substantially the same operating frequency, the second transmitter antenna tilted with respect to the longitudinal axis;   a receiver antenna located along the longitudinal axis and tilted with respect to the longitudinal axis, the receiver antenna disposed a first distance from the first transmitter antenna, a first reference point being located along the first distance and approximately equidistant from the first transmitter and the receiver antenna, the receiver antenna disposed at a second distance, substantially equal to the first distance, from the second transmitter antenna, a second reference point being located along the second distance and approximately equidistant from the second transmitter and the receiver antenna, the receiver antenna configured to provide a first plurality of electromagnetic measurements associated with the first reference point and a second plurality of electromagnetic measurements associated with the second reference point; and   a drill bit, including a depth measurement device, wherein the depth measurement device is a located at a predetermined distance from at least one of the first or second reference points; and   a processing unit configured to control activation of the transmitter antennas and receiver antennas and to process the first and second plurality of electromagnetic measurements associated with the transmitter antennas and receiver antennas.   
     
     
         31 . A method of aligning a plurality of downhole electromagnetic measurements, comprising:
 obtaining a drill bit depth of a drill bit at an initial recording time;   collecting a first plurality of electromagnetic measurements at an operating frequency from a first tilted transmitter antenna and a first tilted receiver antenna, separated from each other by a first longitudinal distance and disposed approximately equidistant about a first reference point, the first reference point located at a second longitudinal distance from the drill bit;   collecting a second plurality of electromagnetic measurements, at substantially the same operating frequency, from a second tilted transmitter antenna and a second tilted receiver antenna, separated by substantially the same first longitudinal distance and disposed approximately equidistant from a second reference point, different than the first reference point;   collecting a third plurality of electromagnetic measurements, at substantially the same operating frequency, from a third tilted transmitter antenna and a third tilted receiver antenna, separated by substantially the same first longitudinal distance and disposed approximately equidistant about a third reference point, different than the first and second reference points;   processing the first, second, and third plurality of electromagnetic measurements to produce a corresponding first, second, and third plurality of higher order mode signals, respectively;   determining a depth of the first reference point, based on the drill bit depth at the initial recording time and the second distance;   aligning the first plurality of higher order mode signals with the second plurality of higher order mode signals in the time-domain by a first time-shift; and   aligning the first plurality of higher order mode signals with the third plurality of higher order mode signals in the time-domain by a second time-shift.   
     
     
         32 . The method of  claim 31 , wherein aligning the first plurality of higher order mode signals with second plurality of higher mode signals includes:
 determining a common parameter, including at least one of a slope, a peak, or a sample variance, of at least a portion of the first plurality of higher order mode signals and at least a portion of the second plurality of higher order mode signals; and   correlating the portion of the first plurality of higher order mode signals and the portion of the second plurality of higher order mode signals in the time-domain based on the common parameter.   
     
     
         33 . The method of  claim 31 , wherein aligning the first plurality of higher order mode signals with the third plurality of higher mode signals includes:
 determining a common parameter, including at least one of a slope, a peak, or a sample variance, of at least a portion of the first plurality of higher order mode signals and at least a portion of the third plurality of higher order mode signals; and   correlating the portion of the first plurality of higher order mode signals and the portion of the third plurality of higher order mode signals in the time-domain based on the common parameter.