# US 11,029,435 B2 · Downhole nonlinear acoustics measurements in rock formations using dynamic acoustic elasticity and time reversal

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- Number: US 11,029,435 B2
- Document ID: US11029435B2
- Status: Granted
- Kind: B2
- Application number: 16/343,969
- Filed: 2017-10-24
- Published: 2019-10-31
- Granted: 2021-06-08
- Earliest claimed: 2016-10-24
- Assignees: Triad National Security, LLC; Chevron U.S.A. Inc.
- Applicants: Triad National Security, LLC; Chevron U.S.A. Inc.
- Inventors: Harvey Edwin Goodman; Timothy James Ulrich, II; Peter Roberts; Marcel C. Remillieux; Paul Allan Johnson; Pierre-Yves Le Bas; Robert A. Guyer
- Web page: https://patentgrep.com/patent/US11029435B2

## CPC

- G01N 15/082: {Investigating permeability by forcing a fluid through a sample}
- G01V 1/50: Analysing data
- E21B 47/107: using acoustic means
- E21B 47/18: through the well fluid {, e.g. mud pressure pulse telemetry}
- E21B 49/00: Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
- G01V 1/306: {for determining physical properties of the subsurface, e.g. impedance, porosity or attenuation profiles}
- G01V 1/3808: {Seismic data acquisition, e.g. survey design}
- G01V 1/3817: {Positioning of seismic devices}
- G01V 1/3826: {dynamic steering, e.g. by paravanes or birds}
- G01V 1/3835: {measuring position, e.g. by GPS or acoustically}
- G01V 2210/6222: Velocity; travel time
- G01V 2210/6248: Pore pressure
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS

## Abstract

Apparatus and methods for measurement of pore pressure in rock formations through an open, or cemented and/or cased, borehole are described. Such measurements are achieved using the Dynamic Acoustic Elasticity (DAE) method for characterizing nonlinear parameters by perturbing a selected rock formation volume with a High Amplitude, Low Frequency (HALF) acoustic strain wave, and probing this volume using a Low Amplitude, High Frequency (LAHF) acoustic wave. Time reversal techniques may be employed for focusing acoustic energy Into the formation in the vicinity of the pipe or open hole.

## Claims

### Claim 1

A method for determining nonlinear hysteretic parameters in a formation through a borehole, comprising:
generating strain in a volume surrounding the borehole by focusing a low frequency, periodic acoustic signal of a first frequency on the volume, the low frequency, periodic acoustic signal having a first amplitude at a first time and a second amplitude at a second time, wherein the first amplitude of the low frequency, periodic acoustic signal generates first strain in the volume and the second amplitude of the low frequency, periodic acoustic signal generates second strain in the volume;
transmitting pulsed, high frequency acoustic signals through the volume simultaneously with the generation of strain in the volume with the low frequency, periodic acoustic signal;
measuring signals generated in the formation in the volume relating to particle velocity or particle acceleration in the formation;
determining the strain in the volume based on the signals generated in the formation in the volume relating to the particle velocity or the particle acceleration in the formation, wherein the strain determined in the volume includes the first strain corresponding to the first amplitude of the low frequency, periodic acoustic signal and the second strain corresponding to the second amplitude of the low frequency, periodic acoustic signal;
measuring time-of-flight of the pulsed, high frequency acoustic signals through the volume as a function of strain within the volume during the generation of strain in the volume with the low frequency, periodic acoustic signal, the time-of-flight of the pulsed, high frequency acoustic signals including a first time-of-flight corresponding to the first strain and a second time-of-flight corresponding to the second strain;
determining change of the time-of-flight of the pulsed, high frequency acoustic signals as the function of the strain in the volume, the change of the time-of-flight of the pulsed, high frequency acoustic signals as the function of the strain in the volume including change from the first time-of-flight corresponding to the first strain to the second time-of-flight corresponding to the second strain; and
determining nonlinear hysteretic parameters α, β, and δ based on the change of the time-of-flight of the pulsed, high frequency acoustic signals as the function of the strain in the volume, wherein the nonlinear hysteretic parameter α relates to strength of hysteresis, the nonlinear hysteretic parameters β, and δ are combinations of third- and fourth-order elastic constants representing acoustoelasticity, and pore pressure in the volume is determined based on the nonlinear hysteretic parameters α, β, and δ.

### Claim 2 (depends on 1)

The method of claim 1, wherein said borehole comprises an open borehole.

### Claim 3 (depends on 1)

The method of claim 1, wherein the low frequency, focused periodic acoustic signal is generated using time reversal.

### Claim 4 (depends on 1)

The method of claim 1, wherein the low frequency, focused periodic acoustic signal is generated using phased arrays of acoustic sources.

### Claim 5 (depends on 1)

The method of claim 1, wherein the high frequency, pulsed acoustic signals are generated in the borehole.

### Claim 6 (depends on 1)

The method of claim 1, wherein the low frequency, focused periodic acoustic signal is generated in the borehole.

### Claim 7 (depends on 1)

The method of claim 1, wherein the particle velocity or the particle acceleration is measured using a non-contact vibrometer or a contact accelerometer.

### Claim 8 (depends on 1)

The method of claim 1, wherein the low frequency periodic acoustic signal is between 1 Hz and 1000 Hz.

### Claim 9 (depends on 1)

The method of claim 1, wherein the high frequency acoustic signal has a frequency between 200 kHz and 1.5 MHz.

### Claim 10 (depends on 1)

The method of claim 1, wherein the hysteresis of the nonlinear hysteretic parameters α, β, and δ as the function of strain in the volume is determined.

### Claim 11 (depends on 10)

The method of claim 10, wherein the pore pressure in the volume is determined further based on the hysteresis of the nonlinear hysteretic parameters α, β, and δ thereof as the function of strain in the volume.

### Claim 12 (depends on 11)

The method of claim 11, further comprising the step of calculating fracture failure of said borehole.

### Claim 13 (depends on 11)

The method of claim 11, further comprising the step of calculating collapse failure of said borehole.

### Claim 14 (depends on 11)

The method of claim 11, further comprising the step of calculating oil recovery performance of said formation.

### Claim 15 (depends on 1)

The method of claim 1, wherein determination of the change of the time-of-flight of the pulsed, high frequency acoustic signals includes determination of a ratio of change in perturbed velocity to linear velocity, and the nonlinear hysteretic parameter α is determined based on the ratio of change in perturbed velocity to linear velocity.

### Claim 16

An apparatus configured to determine nonlinear hysteretic parameters in a formation through a borehole, comprising:
a transceiver trained to focus time-reversed acoustic signals in a focal volume centered on said borehole and generate strain in the focal volume, wherein a first strain at a first amplitude is generated in the focal volume at a first time and a second strain at a second amplitude is generated in the focal volume at a second time;
a probe source comprising a transmitting transducer configured to transmit high frequency acoustic pulses into the focal volume while the transceiver focuses the time-reversed acoustic signals in the focal volume;
a receiver comprising a receiving transducer configured to receive, from the focal volume, the high frequency acoustic pulses transmitted by the probe source;
a signal processor configured to determine time-of-flight of the received high frequency acoustic pulses; and
a sensor disposed in the borehole configured to generate signals conveying particle velocity or particle acceleration;
wherein:
the strain in the focal volume is determined based on the signals conveying the particle velocity or the particle acceleration, wherein the strain determined in the focal volume includes the first strain corresponding to the first amplitude at the first time and the second strain corresponding to the second amplitude at the second time;
the time-of-flight of the received high frequency acoustic pulses include a first time-of-flight corresponding to the first strain and a second time-of-flight corresponding to the second strain;
change of the time-of-flight of the received high frequency acoustic pulses as the function of the strain in the focal volume is determined, the change of the time-of-flight of the received high frequency acoustic pulses as the function of the strain in the focal volume including change from the first time-of-flight corresponding to the first strain to the second time-of-flight corresponding to the second strain;
nonlinear hysteretic parameters α, β, and δ are determined based on the change of the time-of-flight of the received high frequency acoustic pulses as the function of the strain in the focal volume, wherein the nonlinear hysteretic parameter α relates to strength of hysteresis, the nonlinear hysteretic parameters β, and δ are combinations of third- and fourth-order elastic constants representing acoustoelasticity; and
pore pressure in the focal volume is determined based on the nonlinear hysteretic parameters α, β, and δ.

### Claim 17 (depends on 16)

The apparatus of claim 16, wherein the high frequency acoustic pulses have a frequency between 200 kHz and 1.5 MHz.

### Claim 18 (depends on 16)

The apparatus of claim 16, wherein said borehole comprises an open borehole.

### Claim 19 (depends on 16)

The apparatus of claim 16, wherein said probe source is disposed within the borehole.

### Claim 20 (depends on 16)

The apparatus of claim 16, wherein said receiver is disposed within the borehole.

### Claim 21 (depends on 16)

The apparatus of claim 16, wherein determination of the change of the time-of-flight of the received high frequency acoustic pulses includes determination of a ratio of change in perturbed velocity to linear velocity, and the nonlinear hysteretic parameter α is determined based on the ratio of change in perturbed velocity to linear velocity.