Imaging of Formation Structure Ahead of the Drill-Bit

• US 20120069713A1
• Filed: 08/16/2011
• Published: 03/22/2012
• Est. Priority Date: 08/23/2010
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Geerits, Theodorus W., Hellwig, Olaf, Bohlen, Thomas
• Granted Patent: US 8,811,114 B2
• Time in Patent Office: Days
• US Class Current: 367/99
• CPC Class Codes: E21B 47/095 by detecting an acoustic anomalies, e.g. using mud-pressure pulses
• CPC Class Codes: G01V 1/48 Processing data

Abstract

The present disclosure is related to apparatuses and methods for downhole acoustic logging. The tool may be used for generating a guided borehole wave that propagates into the formation as a body wave, reflects from an interface, and is converted back into a a guided borehole wave. Guided borehole waves resulting from reflection of the body wave are used to image a reflector. Methods may include processing of acoustic logging signals including: wavefield separation, auto-correlation of wavefield components, filtering using a dip filter, and estimating a distance to the reflective interface.

Claims

1. A method of determining a distance to an interface in an earth formation, the method comprising:

conveying a logging instrument into a borehole;

activating at least one transmitter on the logging instrument to produce a guided acoustic wave which propagates downward to the bottom of the borehole and produces an acoustic wave in the earth formation;

using at least one receiver on the logging instrument to;

receive a first signal responsive to the downward propagating guided acoustic wave, and

receive a second signal responsive to an upward propagating guided acoustic wave resulting from reflection of the acoustic wave in the formation at an interface therein;

filtering the first signal and the second signal using a dip filter; and

estimating from the filtered first signal and the filtered second signal a distance to the interface.

2. The method of claim 1 further comprising:

separating a total wavefield in UP and DOWN-going waves;

auto-correlating the DOWN and UP-going waves;

applying a median filter to auto-correlated Common Shot Gathers (CSG) deconvolving the auto-correlated and filtered UP-going wavefield by the auto correlated and dip filtered DOWN-going wavefield; and

applying a median filter to the auto-correlated Common Receiver Gather (CRG).

3. The method of claim 1 further comprising:

estimating a dip angle and an azimuth of the interface and

imaging the reflector by migration.

4. The method of claim 1 further comprising decomposing the guided acoustic wave into its multipole constituents.

5. The method of claim 1 further comprising performing a phase shift migration using an apparent slowness of observed reflections.

6. The method of claim 1 wherein the acoustic wave in the formation further comprises a shear wave.

7. The method of claim 1 further comprising:

activating the transmitter in at least one multipole mode.

8. The method of claim 1 wherein estimating the distance to the interface further comprises applying a dispersion correction

9. The method of claim 1 further comprising:

controlling a direction of drilling using the determined distance.

10. An apparatus configured to estimate a distance to an interface in an earth formation, the apparatus comprising:

a logging instrument configured to be conveyed into a borehole;

at least one transmitter on the logging instrument configured to produce a guided acoustic wave which propagates downward to the bottom of the borehole and produces an acoustic wave in the earth formation;

at least one receiver on the logging instrument configured to;

receive a first signal responsive to the downward propagating guided acoustic wave, and

receive a second signal responsive to an upward propagating guided acoustic wave resulting from reflection of the acoustic wave at the borehole bottom and in the formation at an interface therein; and

at least one processor configured to;

filter the first signal and the second signals using a dip filter, and

estimate from the first signal and the second signal a distance from the bottom of the borehole to the interface,

11. The apparatus of claim 10 wherein the at least one processor is further configured to estimate a dip angle and an azimuth of the interface.

12. The apparatus of claim 10 wherein the guided acoustic wave further is a multipole wave mode.

13. The apparatus of claim 10 wherein the at least one transmitter further comprises a plurality of transmitters that are at least one of:

(i) axially disposed on the logging instrument, and (ii) circumferentially disposed on the logging instrument.

14. The apparatus of claim 10 wherein the at least one processor is further configured to perform a phase shift migration using an apparent slowness of an observed reflection. W

15. The apparatus of claim 10 wherein the acoustic wave in the formation further comprises a shear wave.

16. The apparatus of claim 10 wherein the at least one processor is further configured to perform a wavefield separation into an UP- and DOWN-going wavefield

17. The apparatus of claim 11 wherein the at least one processor is further configured to control a direction of drilling using the determined distance.

18. The apparatus of claim 11 further comprising a conveyance device configured to convey a downhole assembly including the logging tool, the conveyance device selected from:

(i) a wireline, and (ii) a drilling tubular.

19. A computer-readable medium product having stored thereon instructions that when read by a processor enable the processor to execute a method, the method comprising:

filtering a first signal and a second signal using a dip filter and estimating a distance from a bottom of a borehole to an interface in an earth formation wherein;

the first signal is produced by a receiver on a logging instrument conveyed in a borehole responsive to a downward propagating guided acoustic wave in the borehole; and

the second signal is produced by the receiver responsive to an upward propagating guided seismic wave in the borehole, the upward propagating wave resulting from reflection of an acoustic wave produced at the bottom of the borehole by the downward propagating guided acoustic wave and reflected at the interface.

20. The computer-readable medium product of claim 19 further comprising at least one of (i) a ROM, (ii) an EAROM, (iii) an EPROM, (iv) an EEPROM, (v) a flash memory, and (vi) an optical disk.