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1. (WO2012092131) STRESS IN FORMATIONS FROM AZIMUTHAL VARIATION IN ACOUSTIC AND OTHER PROPERTIES
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CLAIMS

What is claimed is:

1. A method for characterizing an earth formation, comprising:

making at least one measurement using a limited aperture source indicative of a principal direction of a near field stress in a borehole penetrating the earth formation; and

obtaining one of: (i) an indication of a principal direction of a far field stress in the earth formation and (ii) a magnitude of a horizontal principal stress;

using the at least one measurement indicative of the principal direction of the near field stress and one of: (i) the indication of the principal direction of the far field stress in the earth formation and (ii) the magnitude of the horizontal principal stress for estimating the other one of: (i) the indication of the principal direction of the far field stress and (ii) the magnitude of the horizontal principal stress.

2. The method of claim 1 wherein the at least one measurement using the limited aperture source further comprises a series of measurements over a range of frequencies over a range of depths of the borehole penetrating the earth formation.

3. The method of claim 1 further comprising making the at least one measurement using the limited aperture source during drilling operations.

4. The method of claim 1 wherein the at least one measurement made by the limited aperture source further comprises at least one of: (i) a compressional wave velocity and (ii) a shear wave velocity.

5. The method of claim 1 wherein the indication of the principal direction of the far field stress is obtained using cross dipole log data.

6. The method of claim 1 further comprising:

marking a selected depth of the formation as having intrinsic anisotropy if, at the selected depth, the magnitude of the difference between the principal direction of the near field stress and the principal direction of the far field stress is less than about 3 degrees.

7. The method of claim 1 further comprising:

marking a selected depth of the borehole as being in a principal stress plane of the earth formation if, at the selected depth, the magnitude of the difference between the principal direction of the near field stress and a normal to the principal direction of the far field stress is less than about 3 degrees.

8. The method of claim 1, if the indication of the principal direction of the far field stress is obtained, further comprising:

estimating a further principal stress direction.

9. The method of claim 1 further comprising estimating a magnitude of a principal stress of the formation using a relation between a velocity of a fast shear mode, a velocity of a slow shear mode, and a relation between the velocity of the fast shear mode, the velocity of the slow shear mode, and two principal stresses in the formation.

10. The method of claim 1 further comprising conducting a further operation selected from: (i) determining a completion type, (ii) designing a completion type, (iii) selecting mud for drilling operations, (iv) designing a casing for completion, (v) determination of economic value of a reservoir, and (vi) evaluation of a risk in pore pressure prediction.

11. The method of claim 1 further comprising:

estimating at least one of: the principal direction of the near field stress, the principal direction of a far field stress, and a vertical stress at the borehole.

12. An apparatus for characterizing an earth formation comprising:

a logging tool configured to obtain at least one limited aperture measurement in a borehole penetrating the earth formation; and at least one processor configured to:

(i) estimate a principal direction of a near field stress near the borehole using the at least one limited aperture measurement; and

(ii) use the estimated principal direction of the near field stress and one of: (i) an indication of a principal direction of a far field stress and (ii) a magnitude of a horizontal principal stress to estimate the other one of: (i) the indication of the principal direction of the far field stress and (ii) the magnitude of the horizontal principal stress.

13. The apparatus of claim 12 wherein the at least one limited aperture measurement further comprises at least one of: (i) a compressional wave velocity and (ii) a shear wave velocity.

14. The apparatus of claim 12 wherein the at least one processor is further configured to:

mark a selected depth of the earth formation as having intrinsic anisotropy if, at the selected depth, a magnitude of a difference between the principal direction of the near field stress and the principal direction of the far field stress is less than about 3 degrees.

15. The apparatus of claim 12 wherein the at least one processor is further configured to mark a selected depth of the borehole as being in a principal stress plane of the formation if, at the selected depth, a magnitude of a difference between the principal direction of the near field stress and a normal to the principal direction of the far field stress is less than about 3 degrees..

16. The apparatus of claim 12 wherein, if the indication of the principal stress direction of the far field is obtained, the at least one processor is further configured to estimate a further principal stress direction.

17. The apparatus of claim 12 wherein the at least one processor is further configured to a magnitude of a principal stress of the formation using a relation between a velocity of the fast shear mode, a velocity of a slow shear mode, and a relation between the velocity of the fast shear mode, the velocity of the slow shear mode, and two principal stresses in the formation.

18. The apparatus of claim 12 wherein the at least one processor is further configured to use conduct a further operation selected from: (i) determining a completion type, (ii) designing a completion type, (iii) selecting mud for drilling operations, (iv) designing a casing for completion, (v) determination of economic value of a reservoir, and (vi) evaluation of a risk in pore pressure prediction.

19. The apparatus of claim 12 further comprising:

a conveyance device configured to convey the logging tool into the borehole, the conveyance device selected from: (i) a wireline, and (ii) a drilling tubular.

20. The apparatus of claim 12 wherein at least one processor is further configured to determine a magnitude of a principal stress of the formation using the principal direction of the near field stress, the principal direction of the far field stress, and a vertical stress at the borehole.

21. A non-transitory machine-readable medium product having stored thereon instructions that, when read by at least one processor, causes the at least one processor to execute a method, the method comprising:

using at least one measurement of claim by a limited aperture source indicative of a principal direction of near field stress in a borehole; and

obtaining one of: (i) an indication of a principal direction of a far field stress in the earth formation and (ii) a magnitude of a horizontal principal stress;

using the at least one measurement indicative of the near field stress direction and one of: (i) the indication of the far field stress direction and (ii) the magnitude of the horizontal principal stress for estimating the other one of: (i) the indication of the principal direction of the far field stress direction and (ii) the magnitude of the horizontal principal stress.

The non- transitory machine-readable medium product of claim 21 further comprising at least one of: (i) a ROM, (ii) an EPROM, (iii) an EEPROM, (iv) a flash memory, and (v) an optical disk.