TH2240A - Equipment and methods for capturing the details of compressed waves generated by multipolar sound waves. - Google Patents

Abstract

This fabricated multipolar acoustic recording apparatus consists of a recording head, an apparatus for generating 2^n polar acoustic waves in the pristine crust surrounding the wellhead but separated from the wellhead by the degraded zone (where n is a greater than zero integer), and an apparatus for detecting the refracted 2^n polar acoustic signal in the principal shape. The wave-generating apparatus consists of four identical piezoelectric hollow cylinders. All four are radially polarized and connected to the recording head in a way that forms a hemispherical shape axially aligned with the recording head. Electrical pulses are applied through the inner and outer cylindrical surfaces of each cylinder. These pulses are polarized in a way that causes adjacent cylinders to vibrate radially in opposite phases. The vibrations of each cylinder generate compressional waves in the wellhead fluid, which interfere to create tetrapolar acoustic waves in the surrounding crust. These sound waves may be deflected in the pristine crust and detected by a transducer. A transducer consists of two detectors in a well spaced apart and a longitudinal wave generator. If the 2^n polar acoustic wave is a compression wave, its compression velocity in the pristine crust can be found from the time interval between the detection of the refracted 2^n polar acoustic wave by the two detectors. If the 2^n polar acoustic wave is a shear wave, its shear velocity in the pristine crust can be determined similarly. The radius of the destroyed zone can be determined from the compression wave velocity in the pristine crust and in the destroyed zone, or from the shear wave velocity in the pristine crust and in the destroyed zone.

Claims (16)

1. Equipment for capturing p-wave velocity details in the pristine crust surrounding the wellhead. This equipment consists of: a housing modified to be lowered into or raised from the wellhead; a transducer within the housing for transmitting P2^n polarized waves into the pristine crust, where n is an integer greater than zero; and a detector within the housing for detecting the reversal of the P2^n polarized waves traveling in the pristine crust at least one location in the wellhead, a axial distance along the wellhead from the transducer. 2. A device under claim 1 in which a 2n-pole P wave is emitted as a quaternary P wave. 3. An apparatus under claim 1 in which a 2n-pole P wave is emitted as an octaponic P wave. 4. The device under Claim 1, which is a signal detection device that detects a reverse polarity P2n wave signal at two locations in the wellhead, spaced longitudinally apart along the wellhead, shall also include a device for measuring the time interval between the detection of the reverse polarity P2n wave signal at these two locations. 5. Equipment for capturing P-wave velocity details in the primitive crust surrounding a wellhead containing fluid. This equipment consists of: a recording head modified for lowering into and raising from the wellhead; a 2n-pole acoustic source attached to the recording head for transmitting 2n-pole P-waves through the fluid into the primitive crust, where n is an integer greater than zero; and a signal detector attached to the recording head, which includes at least one detector for detecting P-wave backwave signals, positioned longitudinally along the wellhead from the source, to detect any significant backwaves of waves originating from the source other than the P-wave backwave. After detecting the P-wave backwave, it can be distinguished from the P-wave backwave. 6. The device under claim 5, which also includes a band filter for eliminating all frequency components of any backwave detected by a detector whose frequency is outside the selected frequency range, where the selected frequency range includes frequencies at which the magnitude of the detected P2n backwave is large relative to the magnitude of any other detected backwave. 7. The device under claim 5, which also includes a device for increasing the distance between 2n-pole sound sources and detecting at least one such signal. 8. The device under claim 6, whose capture head consists of a separable section incorporating a first section containing a 2n-pole acoustic wave source and at least one such signal detector, can be enhanced by adding a barrier between such first and second section. 9. An apparatus under claim 5 in which a 2n-pole acoustic wave source is a quaternary source. 10. An apparatus under claim 5 in which a 2n-pole acoustic wave source is an octaponic source. 11. A method for capturing the P-velocity of the pristine crust surrounding a wellhead but separated from the wellhead by a degraded zone. This method consists of the following steps: (a) transmitting a 2n-polar P-wave from a point in the wellhead into the pristine crust, where n is an integer greater than zero; (b) measuring the P-velocity in the pristine crust by detecting a 2n-polar P-wave reversal signal at a point in the wellhead longitudinally away from the transmission point; and (c) repeating steps (a) and (b) by increasing the distance between the transmission point and the detection point until the P-velocities measured in two consecutive measurements are equal. This measured P-velocity is the P-velocity in the pristine crust. 12. A method for capturing P-velocities in the pristine crust surrounding a wellhead but separated from it by a degraded zone. This method consists of the following steps: (a) transmitting a 2n-polar P-wave from a point in the wellhead into the pristine crust, where n is an integer greater than zero; (b) measuring the P-velocity of the pristine portion of the crust beyond the wellhead by detecting P-wave reversal signals at least two locations in the wellhead, one at a distance from the transmission point and one from each other along the length of the wellhead; and measuring the time interval between the detection of the 2n-polar P-wave reversal signals at at least two such locations; and (c) repeating steps (a) and (b) with increasing distances between the transmission point and the two detection locations to find the P-velocity in the pristine portion of the crust beyond the wellhead until the P-velocities measured in the two consecutive measurements are equal. This measured P-velocity is the P-velocity of the pristine crust. 13. Method for determining the radius of the degraded zone of the crust surrounding a wellhead, where the original crust surrounds the wellhead and is separated from it by this degraded zone. This method consists of the following steps: (a) Transmission of a P2n polar wave from a point in the wellhead into the surrounding crust, where n is an integer greater than zero; (b) Measurement of the P wave velocity of the degraded zone at the first point away from the wellhead by detecting the P2n polar wave reversal signals at two separate points in the wellhead, oriented longitudinally along the wellhead, and measuring the time interval between the detection of the P2n polar wave reversal signals at the first and second points; and increasing the distance between the transmission points; (c) Repeating steps (a) and (b) by increasing the distance between the transmission point and the first point, and between the transmission point and the second point, in order to measure the velocity. The P-velocity of the depleted zone of the Earth's crust is measured at increasing distances from the borehole until the measured P-velocities in two consecutive measurements are equal. The radius of the depleted zone of the Earth's crust can be expressed as: (z/2)(((Cv/Ci)-1)((Cv/Ci)+1))1/2, where z is the minimum distance between the transmission point and the first position, and between the transmission point and the second position where a constant P-velocity is measured, Cv is the P-velocity in the original crust, and Ci is the P-velocity in the depleted zone. 14. A method for capturing S-velocity details in the pristine crust surrounding a wellhead but separated from it by a degraded zone. The method consists of the following steps: (a) transmitting a 2n-polar S-wave from a point in the wellhead into the degraded zone, where n is an integer greater than zero; (b) measuring the S-velocity in the degraded zone by detecting a reversal signal of the 2n-polar S-wave at a point in the wellhead longitudinally away from the transmission point; and (c) repeating steps (a) and (b) by increasing the distance between the transmission point and the detection point until the S-velocities measured in two consecutive measurements are equal. This measured S-velocity is the S-velocity in the pristine crust. 15. A method for capturing S-velocity details in the pristine crust surrounding a wellhead but separated from the wellhead by a degraded zone. This method consists of the following steps: (a) transmitting a 2n-polar S-wave from a point in the wellhead into the degraded zone, where n is an integer greater than zero; (b) measuring the S-velocity in a section of the pristine crust zone further away from the wellhead by detecting S-wave reversal signals at two locations in the wellhead, one at a distance from the transmission point and one between them in the longitudinal direction of the wellhead, and measuring the time interval between the detection of the 2n-polar S-wave reversal signals at these two locations; and (c) repeating steps (a) and (b) by progressively increasing the distance between the transmission point and the two detection locations in order to measure the S-velocity in the section of the pristine crust zone further away from the wellhead until the S-velocity measured in the two measurements is equal. Consecutive occurrences of equal value, and the measured S-wave speed, is the S-wave speed in the original Earth's crust. 16. A method for determining the radius of the depleted zone of the crust surrounding a wellhead, where the original crust surrounds the wellhead and is separated from it by this depleted zone. This method consists of the following steps: (a) Transmission of an S²ⁿ polar S wave from a point in the wellhead into the surrounding crust, where n is an integer greater than zero; (b) Measurement of the S wave velocity of the depleted crust zone by detecting the S²ⁿ polar S wave reversal signals at two positions in the wellhead, one at a distance from the transmission point and one from each other in the longitudinal direction of the wellhead, and measuring the time interval between the detection of the S²ⁿ polar S wave reversal signals at the first and second positions; and (c) Repeating steps (a) and (b) by increasing the distance between the transmission point and the first position, and between the transmission point and the second position, in order to measure the S wave velocity of the depleted crust zone. The radius of the destroyed zone of the crust is progressively increased away from the borehole until the measured S-velocities in two consecutive measurements are equal. The radius of the destroyed zone of the crust can be expressed as: (z/2)(((Cv/Ci)-1)((Cv/Ci)+1))1/2, where z is the distance between the aforementioned transmission point and the first such point and between the transmission point and the second such point, which has the smallest value at which a constant S-velocity is measured, Cv is the S-velocity in the original crust, and Ci is the S-velocity in the destroyed zone. (Clause 16, page 6, figure 12)