Data processing systems and methods for downhole seismic investigations

Patent metadata

Field	Value
Publication number	US-9523784-B2
Application number	US-201213719054-A
Country	US
Kind code	B2
Filing date	Dec 18, 2012
Priority date	Dec 18, 2012
Publication date	Dec 20, 2016
Grant date	Dec 20, 2016

Abstract

Methods and systems for investigating a formation surrounding a wellbore. The methods involve a semblance-based analysis of downhole data, for example low frequency downhole data. The semblance-based analysis includes group semblance mapping of the data, followed by single shot semblance map handling, followed by multiple shot data handling. The systems include a seismic source, a seismic receiver, and an electronics system for processing data according to a process including: group semblance mapping, single shot map handling, and multiple shot data handling. The seismic source may generate low frequency signals, and the seismic receiver may be two or more receiver subsystems that include at least two axially spaced-apart hydrophones and at least one multi-component geophone.

First claim

What is claimed is:

1. A method for investigating a formation surrounding a wellbore, comprising:
a) firing a seismic source located downhole or at surface;
b) recording data relating to acoustic waves generated by the seismic source using one or more groups of downhole receivers, wherein each group has one or more receivers; and
c) processing the data according to a semblance technique comprising group semblance mapping, the group semblance mapping comprising processing signals from a plurality of the receivers to determine consistent signals related to a same seismic event, the processing comprising sliding an observation time window of a given width along a time axis.

2. A method according to claim 1 , wherein when the semblance technique is performed on data recorded by multiple receiver subsystems, the recorded data is normalized to a common reference axis using a coordinate rotation process.

3. A method according to claim 1 , further comprising: optimizing a number of the downhole receivers in the groups.

4. A method according to claim 1 , further comprising: identifying a location, orientation, or both of ten or fewer bed boundaries, which are up to about 500 meters around and ahead of the wellbore.

5. A method according to claim 1 , wherein the seismic source comprises: at least two force generating members retractably connected to a drill-string tubular at substantially a same axial position; and a control system for activating the at least two force generating members to engage the wellbore and transmit a seismic signal comprising a swept frequency signal ranging up to about 700 Hz into the formation surrounding the wellbore.

6. A method according to claim 1 , wherein each of the one or more groups of downhole receivers comprises at least two, same-type, axially spaced-apart hydrophones affixed to a drill-string tubular, at least one multi-component geophone, and mechanical elements for stable acoustic coupling of receivers to a seismic signal travelling in the surrounding formation.

7. A method according to claim 6 , wherein the one or more groups of downhole receivers comprise two to four groups.

8. A method according to claim 1 , wherein the recorded data corresponds to acoustic waves generated by a low frequency source of frequencies ranging from about 5 Hz to about 500 Hz.

9. A method according to claim 1 , wherein the group semblance mapping is performed by one or more downhole processors.

10. A method according to claim 1 , wherein group semblance mapping comprises: generating a semblance map for each group of receivers, and at least partially removing noise from each semblance map to create cleaned group semblance maps; and creating a cleaned single shot semblance map by stacking the cleaned group semblance maps.

11. A method according to claim 1 , wherein data related to each reflector detected by semblance mapping at group level is integrated among multiple groups at a shot level by determining a reflector that allows minimization of a fitting error function.

12. A method according to claim 11 , wherein the error function is a distance error determined from an ellipse position for reflector(s) in each group that is weighted by semblance peak amplitude, sharpness, peak RMS amplitude, or a combination thereof.

13. A method according to claim 1 , further comprising performing 3D positioning of reflectors by determining the reflectors in two independent planes containing locally and approximately the wellbore at an intersection of the two planes, wherein the reflectors have a common intersection at the intersection of the two planes.

14. A method according to claim 1 , wherein additional waves travelling parallel to the wellbore are also detected, allowing noise reduction and determination of seismic velocities in the formation for determination of distance of a reflector close to the wellbore.

15. A method according to claim 1 , wherein seismic signals travelling across the formation comprise P-waves, S-waves, refraction waves or combinations thereof.

16. A system for investigating a formation surrounding a wellbore, comprising:
a seismic source;
one or more groups of downhole receivers, wherein each group of receivers comprises one or more receivers;
a surface electronics subsystem; and
a downhole electronics subsystem, wherein the surface and downhole electronics subsystem are configured to cooperate in processing data recorded by the one or more groups of receivers according to a process comprising group semblance mapping to detect a location, orientation, or both of up to ten bed boundaries and up to about 500 meters around or ahead of the wellbore, the group semblance mapping comprising processing signals from a plurality of the receivers to determine consistent signals related to a same seismic event, the processing comprising sliding an observation time window of a given width along a time axis.

17. A system according to claim 16 , further comprising: at least one sensor configured to determine orientation of each of the one or more groups of receivers relative to an earth gravity vector, an earth magnetic vector or both.

18. A system according to claim 16 , wherein the seismic source comprises: at least two force generating members retractably connected to a drill-string tubular at substantially a same axial position; and a control system for activating the at least two force generating members to engage the wellbore and transmit a seismic signal comprising a swept frequency signal ranging up to about 700 Hz into the formation surrounding the wellbore.

19. A system according to claim 18 , wherein the swept frequency ranges from about 5 Hz to about 500 Hz.

20. A system according to claim 16 , wherein each of the one or more groups of downhole receivers comprises at least two, same-type, axially spaced-apart hydrophones affixed to a drill-string tubular, at least one multi-component geophone, and mechanical elements for stable acoustic coupling of receivers to a seismic signal travelling in the surrounding formation.

Assignees

• Schlumberger Technology Corp

Inventors

• Orban Jacques

Classifications

• G01V2210/60

  Analysis · CPC title

• G01V1/50

  Analysing data · CPC title

• G01V1/48

  Processing data · CPC title

• G01V1/40 Primary

  specially adapted for well-logging · CPC title