Downhole tomographic imaging

Patent metadata

Field	Value
Publication number	US-10240451-B2
Application number	US-201415502534-A
Country	US
Kind code	B2
Filing date	Oct 2, 2014
Priority date	Oct 2, 2014
Publication date	Mar 26, 2019
Grant date	Mar 26, 2019

Abstract

A tomographic imaging apparatus utilizes Compton backscattering to evaluate cement behind the casing. The imaging apparatus includes a slant-hole or pin-hole collimator coupled to a series of detectors in order to count the number of photons that backscatter off from the cement. The number of backscattered photons is proportional to the density of the cement behind the casing. Using the photon count, an image processing unit of the imaging apparatus generates a 2D or 3D tomographic image of the borehole.

First claim

What is claimed is:

1. An apparatus for downhole photon imaging, comprising:
a photon source that emits photons;
a first detector module positioned above the photon source, the first detector module comprising a plurality of photon detectors to detect photons and produce a signal in response to the received photons, wherein each detector is positioned to correspond to a different depth of investigation;
a first detector collimator coupled to the detectors to allow backscattered photons at a pre-determined angle to be detected by the detectors of the first detector module;
a second detector module positioned below the photon source, the second detector module comprising a plurality of photon detectors to detect photons and produce a signal in response to the received photons, wherein each detector of the second detector module is positioned to correspond to a different depth of investigation;
a second detector collimator coupled to the detectors of the second detector module to allow backscattered photons at a pre-determined angle to be detected by the second detector module; and
an image processing unit that generates an image of a wellbore surrounding the apparatus based upon the signal produced by the detectors of at least one of the first detector module or the second detector module.

2. An apparatus as defined in claim 1 , wherein the first detector collimator comprises a plurality of slant holes positioned at an angle in relation to an axis of the apparatus, wherein each slant hole is positioned to direct backscattered photons to a single detector in the first detector module.

3. An apparatus as defined in claim 1 , wherein the detector collimator comprises a pin hole positioned to direct backscattered photons to all detectors in the first detector module.

4. An apparatus as defined in claim 1 , wherein the image processing unit is a two-dimensional tomographic image processing unit.

5. An apparatus as defined in claim 1 , wherein the first detector collimator is configured to accept photons having single Compton backscattering.

6. An apparatus as defined in claim 1 , wherein the photon source emits photons at one or more energy levels, or over a range of energy levels.

7. An apparatus as defined in claim 1 , wherein the photon source is a chemical source, induced gamma-rays from neutron activation, or an electronic source.

8. An apparatus as defined in claim 1 , wherein the image of the wellbore is a defect in cement behind a casing.

9. A method for downhole photon imaging, comprising:
(i) emitting photons from a photon source, wherein the photons are backscattered from a region of interest surrounding a wellbore;
(ii) receiving the backscattered photons within a first detector collimator positioned at a pre-determined angle;
(iii) directing the backscattered photons through the first detector collimator and onto a first detector module, the first detector module comprising a plurality of photon detectors to detect the backscattered photons and generate a first signal;
(iv) receiving the backscattered photons within a second detector collimator positioned at a pre-determined angle;
(v) directing the backscattered photons through the second detector collimator and onto a second detector module, the second detector module comprising a plurality of photon detectors to detect the backscattered photons and generate a second signal; and
(vi) utilizing at least one of first signal or the second signal to generate an image of the region of interest.

10. A method as defined in claim 9 , wherein receiving the backscattered photons within the first detector collimator comprises:
receiving the backscattered photons through a plurality of slant holes, wherein each slant hole is positioned to direct backscattered photons to a single detector; and
directing the backscattered photons through the slant holes and to the detectors.

11. A method as defined in claim 9 , wherein receiving the backscattered photons within the first detector collimator comprises:
receiving the backscattered photons through a pin hole; and
directing the backscattered photons to each detector of the first detector module.

12. A method as defined in claim 9 , wherein the image is a two-dimensional tomographic image generated by an imaging apparatus.

13. A method as defined in claim 12 , wherein utilizing further comprises:
rotating the imaging apparatus; and
repeating (i)-(vi) to generate the image as the imaging apparatus is rotated.

14. A method as defined in claim 13 , further comprising moving the imaging apparatus along the wellbore to generate a three-dimensional tomographic image of the region of interest.

15. A method as defined in claim 9 , wherein generating the image comprises generating an image of a defect in cement behind casing.

16. A method as defined in claim 9 , wherein the backscattered photons received by the first detector collimator are photons having single Compton backscattering.

17. A method as defined in claim 9 , wherein generating the image comprises:
obtaining a radial spectrum of the region of interest using at least one of the first signal or the second signal;
obtaining a reference spectrum of the region of interest;
normalizing the radial spectrum using the reference spectrum; and
generating the image using the normalized radial spectrum.

18. A method as defined in claim 12 , wherein the imaging apparatus is positioned along a logging, drilling, or wireline assembly.

Assignees

• Halliburton Energy Services Inc

Inventors

• Lee Dongwon
• Guo Weijun
• Srinivasan Sriram

Classifications

• E21B47/005 Primary

  Monitoring or checking of cementation quality or level · CPC title

• E21B33/14

  for cementing casings into boreholes · CPC title

• G21K1/02

  using diaphragms, collimators · CPC title

• G01V5/101

  and detecting the secondary Y-rays produced in the surrounding layers of the bore hole · CPC title

• E21B47/0002

  Fixed Constructions · mapped topic