SOURCE COMPENSATED FORMATION DENSITY MEASUREMENT METHOD BY USING A PULSED NEUTRON GENERATOR

• US 20100314535A1
• Filed: 06/09/2010
• Published: 12/16/2010
• Est. Priority Date: 06/10/2009
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Zhang, Qianmei, Chalitsios, Constantyn
• Granted Patent: US 8,598,510 B2
• Time in Patent Office: Days
• US Class Current: 250/252.1
• CPC Class Codes: G01V 5/101 and detecting the secondary Y-rays produced in the surrounding layers of the bore hole

Abstract

A downhole instrument for estimating density of sub-surface materials includes: a neutron source, a source monitoring detector, a near detector and a far detector. Each of the detectors may be coupled to an electronics unit adapted for receiving a detection signal from each of the detectors and compensating the detection signal for at least one of the near detector and the far detector according to the detection signal of the source monitoring detector. A method for estimating density is provided.

Claims

1. A downhole instrument for estimating density of sub-surface materials, the instrument comprising:

a neutron source, a source monitoring detector, a near detector and a far detector, each of the detectors coupled to an electronics unit adapted for receiving a detection signal from each of the detectors and compensating the detection signal for at least one of the near detector and the far detector according to the detection signal of the source monitoring detector.

2. The instrument as in claim 1, wherein the electronics unit is coupled to the neutron source for monitoring a production of neutrons.

3. The instrument as in claim 1, wherein the electronics unit is equipped to identify gamma rays in at least one detector in at least one of a coincident mode and an anti-coincident mode.

4. The instrument as in claim 1, wherein the neutron source comprises a pulsed neutron generator.

5. The instrument as in claim 1, the electronics unit further comprising instructions for estimating a density according to a compensated detection signal for at least one of the near detector and the far detector.

6. The instrument as in claim 1, wherein the source monitoring detector provides monitoring of the production of neutron induced inelastic gamma rays.

7. The instrument as in claim 1, wherein the electronics unit comprises an input for receiving a production signal from the source.

8. The instrument as in claim 6, wherein electronics unit provides the compensating according to the production signal.

9. The instrument as in claim 6, wherein the production signal comprises at least one of source strength and an energy spectrum.

10. The instrument as in claim 1, wherein the detection signal from at least one of the near detector and the far detector comprises information regarding backscattered inelastic gamma rays.

11. The instrument as in claim 10, wherein the coincident mode identifies inelastic gamma rays and the anti-coincident mode identifies neutron capture gamma rays.

12. The instrument as in claim 1, wherein the electronics unit is further adapted for binning detection events within each of the detection signals.

13. The instrument as in claim 1, wherein the detection signal for at least one of the near detector and the far detector is compensated according to a detection signal of the source monitoring detector.

14. The instrument as in claim 1, wherein at least one detector comprises at least one of a collimator and surrounding shielding.

15. A method for estimating a density of sub-surface materials, the method comprising:

irradiating the sub-surface materials with a neutron source;

detecting gamma rays from the irradiating;

detecting gamma rays returning from the sub-surface materials;

compensating a signal representing the returning gamma rays according to a signal for the gamma rays from the irradiating; and

estimating the density of the sub-surface materials according to the compensated signal.

16. The method as in claim 15, wherein detecting the returning gamma rays comprises collecting a detection signal for at least one of the near detector and the far detector.

17. The method as in claim 15, wherein compensating comprises at least one of adjusting a detection signal for a near detector and a detection signal for a far detector according to a detection signal for a detector proximate to the neutron source.

18. The method as in claim 15, wherein compensating comprises at least one of adjusting a detection signal for a near detector and a detection signal for a far detector according to a production characteristic of the neutron source.

19. The method as in claim 15, further comprising placing the neutron source proximate to the sub-surface materials by using one of a drilling apparatus and a wireline apparatus.

20. The method as in claim 15, wherein estimating a density comprises estimating a density using compensated data from at least one of a near detector, a far detector and a combination of the near detector and the far detector.