Method for computing dip of earth formations from wellbore image data

• US 5,983,163 A
• Filed: 09/04/1998
• Issued: 11/09/1999
• Est. Priority Date: 09/04/1998
• Status: Expired due to Term

• Current Assignee: Western Atlas International Incorporated (Northrop Grumman Corporation)
• Original Assignee: Western Atlas International Incorporated (Northrop Grumman Corporation)
• Inventors: Priest, John F., Waid, Charles Carter
• Primary Examiner(s): Oda, Christine
• Assistant Examiner(s): Taylor, Victor J.
• Application Number:
  US09/148,399
• Time in Patent Office: 431 Days
• Field of Search: 702/106, 702/117, 702/111, 702/110, 702/10, 367/125, 367/134, 324/355.5, 324/333.3
• US Class Current: 702/10
• CPC Class Codes: G01V 3/38 Processing data, e.g. for analysis, for interpretation, for correction

Abstract

A method for calculating the orientation of a geologic feature with respect to the axis of a wellbore drilled through earth formations. The method uses finely detailed measurements of a selected property of the earth formations made along the wall of the wellbore. The method includes the steps of segregating the finely detailed measurements by an angle subtended with respect to an arbitrary reference on the circumference of the wellbore. The measurements are further segregated into a selected axial interval along the wellbore. For each segment, for each subtended angle, the segregated measurements are spectrally analyzed with respect to spatial frequency. Coefficients of a best fit curve are determined for the phase components of the spectrally analyzed measurements with respect to the subtended angle. The orientation of the geologic feature is calculated from the best fit curve. In the preferred embodiment a noise floor is calculated in each segment by stacking the amplitude components at each spatial frequency in each interval. For each spatial frequency, the stacked amplitude is compared to the noise floor. Only spatial frequencies having amplitudes above the noise floor are used to generate the best fit curve from their respective phase components.

Claims

1. A method for determining an orientation of a geologic feature with respect to the axis of a wellbore drilled through earth formations using circumferentially spaced apart measurements of a selected property of said earth formations made along the wall of the wellbore, the method comprising:

segregating said measurements by an angle subtended with respect to a selected reference along said wall of said wellbore;

segregating measurements into a selected axial interval along said wellbore;

transforming the segregated measurements in a direction of the axial interval to give transformed measurements having a phase as a function of spatial frequency,

spectrally analyzing said transformed measurements segregated with respect to said subtended angle and said axial interval with respect to the spatial frequency;

determining coefficients which define a best fit curve of the phase components of said spectrally analyzed measurements with respect to said subtended angle; and

calculating said orientation from said best fit curve.

2. The method as defined in claim 1 further comprising;

averaging in each said interval amplitude components of said spectrally analyzed measurements for each spatial frequency;

determining a noise floor from said averaged amplitude components;

selecting ones of said frequencies wherein said averaged amplitude components exceeds said noise floor; and

determining said coefficients of said best fit curve from phase components of said selected ones of said frequencies.

3. The method as defined in claim 1 further comprising:

calculating an average wellbore radius for each said subtended angle over each segment;

dividing said phase components for each said subtended angle in each said segment by said average wellbore radius for said subtended angle.

4. The method as defined in claim 1 wherein said selected property comprises acoustic reflectance amplitude.

5. The method as defined in claim 1 wherein said selected property comprises electrical resistivity.

6. The method as defined in claim 1 further comprising converting said orientation with respect to said axis of said wellbore and said arbitrary reference to an orientation with respect to gravity and a geographic reference.

7. A method for calculating an orientation of a geologic feature with respect to the axis of a wellbore drilled through earth formations, comprising:

inserting a well logging instrument into said wellbore, said instrument adapted to measure a selected property of said earth formations at a plurality of circumferentially spaced apart locations around a wall of said wellbore;

measuring said selected property of the earth formations made along the wall of said wellbore at said plurality of circumferentially spaced apart locations around said wall of said wellbore;

segregating said circumferentially spaced apart measurements by an angle subtended with respected to a selected reference along the circumference of said wellbore;

transforming the segregated measurements in a direction of the axial interval to give transformed measurements having a phase as a function of spatial frequency,

spectrally analyzing said transformed measurements segregated with respect to subtended angle and said axial interval with respect to the spatial frequency;

determining coefficients which define a best fit curve of phase components of said spectrally analyzed measurements with respect to said subtended angle; and

calculating said orientation from said best fit curve.

8. The method as defined in claim 7 further comprising;

averaging in each said interval amplitude components of said spectrally analyzed measurements for each spatial frequency;

determining a noise floor from said averaged amplitude components;

selecting ones of said frequencies wherein said averaged amplitude components exceeds said noise floor; and

determining said coefficients of said best fit curve from phase components of said selected ones of said frequencies.

9. The method as defined in claim 7 further comprising:

calculating an average wellbore radius for each said subtended angle over each segment;

dividing said phase components for each said subtended angle in each said segment by said average wellbore radius for said subtended angle.

10. The method as defined in claim 7 wherein said selected property comprises acoustic reflectance amplitude.

11. The method as defined in claim 7 wherein said selected property comprises electrical resistivity.

12. The method as defined in claim 7 further comprising converting said orientation with respect to said axis of said wellbore and said arbitrary reference to an orientation with respect to gravity and a geographic reference.