Shear wave source for VSP and surface seismic exploration

Patent metadata

Field	Value
Publication number	US-10310118-B2
Application number	US-201214378310-A
Country	US
Kind code	B2
Filing date	Nov 30, 2012
Priority date	Feb 14, 2012
Publication date	Jun 4, 2019
Grant date	Jun 4, 2019

Abstract

Seismic shear-wave survey systems and methods that employ inclined borehole pairs with directional detonations. If the boreholes have substantially equal inclinations in opposite azimuthal directions, the resulting signal traces can be combined to isolate shear wave energy contributions, thereby offering potentially enhanced resolution and reduced-complexity interpretation. The boreholes may be cased to ensure repeatability for, e.g., monitoring of reservoir fracturing, treatments, and/or drainage. The directional charges may be immersed to improve coupling of seismic energy into the formation.

First claim

What is claimed is:

1. A method of surveying with seismic shear waves, the method comprising:
generating the seismic shear waves with directional detonations detonated separately but at approximately a same time, the directional detonations in a pair of inclined boreholes that cross from a side profile but do not intersect and have similar inclination angles of approximately 45° from vertical in opposite azimuthal directions;
acquiring signals representative of a receiver array's response to each of the pair of directional detonations;
subtracting the response signals to suppress compressional wave information and enhance shear wave information; and
displaying a subsurface log or image derived from the subtracted responses, wherein the acquired signals reflect a diffraction or scattering of the generated seismic shear waves as they pass through a fluid-filled fracture in a formation being surveyed.

2. The method of claim 1 , further comprising:
obtaining a second pair of inclined boreholes at azimuths orthogonal to the first pair;
providing in each of the second pair of inclined boreholes one of a second pair of directional detonations;
acquiring additional signals representative of the receiver array's responses to each of the second pair of directional detonations; and
combining the additional response signals to suppress additional compressional wave information and enhance additional shear wave information.

3. The method of claim 1 , wherein the receiver array is a surface array.

4. The method of claim 1 , wherein the receiver array is deployed in an additional borehole.

5. The method of claim 1 , wherein the inclined boreholes are cased.

6. The method of claim 1 , wherein said providing a directional detonation includes immersing a broomstick charge in liquid at the bottom of at least one of the boreholes.

7. The method of claim 1 , wherein the bottoms of the boreholes in each pair are within 10 meters of each other.

8. The method of claim 1 , further comprising:
processing the responses further to obtain compressional wave information with shear wave information suppressed; and
displaying a subsurface image derived from the compressional wave information.

9. The method of claim 1 , further comprising:
repeating directional detonations in each inclined borehole;
acquiring the receiver array's responses to the repeated directional detonations;
separating the shear wave information into slow and fast shear wave components; and
displaying the slow shear wave information as at least part of the derived subsurface log or image.

10. The method of claim 9 , wherein the directional detonations in each inclined borehole are repeated at a given time interval.

11. The method of claim 1 , further comprising:
repeating the providing of the directional detonations and the acquiring of the responses before or after a pump used to hydraulically fracture a formation being surveyed is shut off;
separating the shear wave information into slow and fast shear wave components; and
displaying the slow shear wave information as at least part of the derived subsurface log or image.

12. The method of claim 11 , further comprising displaying the slow shear wave information as a time-lapse sequence.

13. The method of claim 11 , further comprising:
subtracting the slow shear wave information acquired during a final repetition at the end of the time period from the slow shear wave information acquired during each prior repetition; and
displaying each subtracting result as at least part of the displaying of the slow shear wave information.

14. A shear wave surveying system that comprises:
a pair of inclined boreholes that cross from a side profile but do not intersect and have similar inclination angles of approximately 45° from vertical in opposite azimuthal directions;
a receiver array that provides data in the form of one or more sets of seismic traces in response to shear waves generated by directional detonations detonated separately but at approximately a same time in each of said boreholes;
a recording system that records each set of seismic traces; and
a processing system that subtracts the sets to extract enhanced shear-wave information and provide a subsurface log or image of subsurface formation structures, wherein the enhanced shear-wave information reflects a diffraction or scattering of the generated shear waves as they pass through a fluid-filled fracture in a formation being surveyed.

15. The system of claim 14 , further comprising:
a second pair of inclined boreholes at azimuths orthogonal to the first pair.

16. The system of claim 14 , wherein the receiver array is a surface array.

17. The system of claim 14 , wherein the receiver array is a vertical seismic profiling array.

18. The system of claim 14 , wherein said boreholes are cased.

19. The system of claim 14 , wherein said boreholes are water-filled.

20. The system of claim 14 , wherein said directional detonations result from broomstick charges.

21. The system of claim 14 , wherein said directional detonations result from a time-sequenced series of charges.

22. The system of claim 14 , wherein the bottoms of the borehole are within 10 meters of each other.

23. The system of claim 14 , wherein the processing system provides time-lapse log or image comparisons derived from repeated detonations in the inclined boreholes.

24. The system of claim 14 , wherein the processing system calculates a difference between slow shear-wave information associated with a final detonation of a plurality of detonations triggered during a given time period and slow shear-wave information associated with each prior detonation of the plurality of detonations, and wherein at least part of the log or images provided is representative of the calculated differences.

25. The system of claim 14 , wherein at least some of the extracted shear-wave information is associated with a plurality of repeated detonations triggered during a given time period before or after a pump used to hydraulically fracture a borehole being surveyed is shut off.

Assignees

• Halliburton Energy Services Inc
• Willis Mark E

Inventors

• Willis Mark E

Classifications

• G01V1/366

  by correlation of seismic signals · CPC title

• G01V1/345 Primary

  Visualisation of seismic data or attributes, e.g. in 3D cubes · CPC title

• G01V1/40

  specially adapted for well-logging · CPC title

• G01V1/006

  generating single signals by using more than one generator, e.g. beam steering or focusing arrays (G01V1/13, G01V1/3861 take precedence) · CPC title

• G01V1/053 Primary

  for generating transverse waves · CPC title