ASSESSING STRESS STRAIN AND FLUID PRESSURE IN STRATA SURROUNDING A BOREHOLE BASED ON BOREHOLE CASING RESONANCE

• US 20130188452A1
• Filed: 01/19/2012
• Published: 07/25/2013
• Est. Priority Date: 01/19/2012
• Status: Abandoned Application

• Current Assignee: Adam Pidlisecky, Andre St-Onge, David Eaton
• Original Assignee: Adam Pidlisecky, David Eaton
• Inventors: ST-ONGE, Andre, EATON, David, PIDLISECKY, Adam
• Application Number:
  US13/353,376
• Publication Number:
  US 20130188452A1
• Time in Patent Office: Days
• US Class Current: 367/35
• CPC Class Codes: G01V 1/50 Analysing data

Abstract

A method of determining a physical property of subsurface strata surrounding a borehole. The physical property includes any one or more of stress, strain of fluid pressure of the subsurface strata. The borehole includes a borehole liner having an interior wall. A pair of sensor modules separated by a known distance are clamped to the interior wall of the borehole liner. The clamping induces an acoustic discontinuity in the borehole liner such that a P-wave propagating longitudinally within the borehole liner is at least partially reflected. A respective sensor of each sensor module detecting P-waves propagating in the liner and generating a corresponding sensor output signal indicative of the detected P-waves. A respective sensor output signal from each sensor module is analyzed to detect a resonance in a section of the borehole liner between the sensors. A fundamental frequency of the detected resonance is determined and analyzed to determine the physical property.

Claims

1. A method of determining a physical property of subsurface strata surrounding a borehole, the physical property comprising any one or more of stress, strain and fluid pressure in the subsurface strata, the borehole including a borehole liner having an interior wall, the method comprising:

clamping a pair of sensor modules separated by a known distance to the interior wall of the borehole liner, the clamping inducing an acoustic discontinuity in the borehole liner such that an elastic wave propagating longitudinally within the borehole liner is at least partially reflected;

a respective sensor of each sensor module detecting elastic waves propagating in the liner and generating a corresponding sensor output signal indicative of the detected P-waves;

analysing a respective sensor output signal from each sensor module to detect a resonance in a section of the borehole liner between the sensors;

determining a fundamental frequency of the detected resonance; and

analysing the fundamental frequency to determine the physical property.

2. The method of claim 1, wherein analysing a respective sensor output signal comprises:

determining a power spectrum of the sensor output signal; and

identifying resonance in the power spectrum.

3. The method of claim 2, wherein determining a power spectrum of the sensor output signal comprises computing a Fast Fourier Transform.

4. The method of claim 2, wherein identifying a resonance in the power spectrum comprises detecting at least one local maximum in the power spectrum.

5. The method of claim 1, wherein analysing the fundamental frequency to determine the strain comprises:

determining a relationship between strain and propagation speed of an elastic wave in the liner;

detecting a change in the fundamental frequency; and

determining the strain based on the detected change in the fundamental frequency and the determined relationship between strain and propagation speed of an elastic wave in the liner.

6. A method of determining stress in a borehole liner, the method comprising:

clamping a pair of sensor modules separated by a known distance to the interior wall of the borehole liner, the clamping inducing an acoustic discontinuity in the borehole liner such that an elastic wave propagating longitudinally within the borehole liner is at least partially reflected;

a respective sensor of each sensor module detecting elastic waves propagating in the liner and generating a corresponding sensor output signal indicative of the detected P-waves;

analysing a respective sensor output signal from each sensor module to detect a resonance in a section of the borehole liner between the sensors;

determining a fundamental frequency of the detected resonance; and

analysing the fundamental frequency to determine the stress.

7. The method of claim 6, wherein analysing a respective sensor output signal comprises:

determining a power spectrum of the sensor output signal; and

identifying a resonance in the power spectrum.

8. The method of claim 7, wherein determining a power spectrum of the sensor output signal comprises computing a Fast Fourier Transform.

9. The method of claim 7, wherein identifying a resonance in the power spectrum comprises detecting at least one local maximum in the power spectrum

10. The method of claim 6, wherein analysing the fundamental frequency to determine the stress comprises:

determining a relationship between stress and propagation speed of an elastic wave in the liner;

detecting a change in the fundamental frequency; and

determining the stress based on the detected change in the fundamental frequency and the determined relationship between stress and propagation speed of an elastic wave in the liner.

11. A system for determining a physical property of subsurface strata surrounding a borehole, the physical property comprising any one or more of stress, strain and fluid pressure in the subsurface strata, the borehole including a borehole liner having an interior wall, the method comprising:

a pair of sensor modules configured to be clamped to the interior wall of the borehole liner and separated by a known distance, the clamping inducing an acoustic discontinuity in the borehole liner such that an elastic wave propagating longitudinally within the borehole liner is at least partially reflected;

a respective sensor of each sensor module detecting elastic waves propagating in the liner and generating a corresponding sensor output signal indicative of the detected elastic waves; and

a surface station configured to;

analyse a respective sensor output signal from each sensor module to detect a resonance in a section of the borehole liner between the sensors;

determine a fundamental frequency of the detected resonance; and

analyse the fundamental frequency to determine the physical property.