High Voltage X-Ray Generator and Related Oil Well Formation Analysis Apparatus and Method

• US 20110002443A1
• Filed: 09/14/2010
• Published: 01/06/2011
• Est. Priority Date: 12/15/2006
• Status: Active Grant

• Current Assignee: Arthur J. Becker, Christian Stoller, Joel L. Groves, Peter Wraight
• Original Assignee: Arthur J. Becker, Christian Stoller, Joel L. Groves, Peter Wraight
• Inventors: Wraight, Peter, Groves, Joel L., Becker, Arthur J., Stoller, Christian
• Granted Patent: US 7,991,111 B2
• Time in Patent Office: Days
• US Class Current: 378/54
• CPC Class Codes: H01J 2235/0233 High tension
• CPC Class Codes: H01J 2235/06 Cathode assembly
• CPC Class Codes: H01J 2235/163 shaped for a particular application
• CPC Class Codes: H01J 35/06 Cathodes
• CPC Class Codes: H05G 1/02 Constructional details
• CPC Class Codes: H05G 1/10 Power supply arrangements for feeding the X-ray tube supply circuits with converters in general H02M; supply circuits for emitters and amplifiers H04B1/16 - H04B1/1623

Abstract

An apparatus and method for determining the density and other properties of a formation surrounding a borehole using a high voltage x-ray generator. One embodiment comprises a stable compact x-ray generator capable of providing radiation with energy of 250 keV and higher while operating at temperatures equal to or greater than 125° C. In another embodiment, radiation is passed from an x-ray generator into the formation; reflected radiation is detected by a short spaced radiation detector and a long spaced radiation detector. The output of these detectors is then used to determine the density of the formation. In one embodiment, a reference radiation detector monitors a filtered radiation signal. The output of this detector is used to control at least one of the acceleration voltage and beam current of the x-ray generator.

Claims

1. A compact x-ray generator comprising:

an electron emitter;

a target; and

a high voltage power supply;

wherein

said x-ray generator provides radiation with energy greater than or equal to 250 keV; and

said x-ray generator operates at temperatures greater than or equal to 125°

C.

2. The compact x-ray generator as defined in claim 1, wherein:

said high voltage power supply comprises;

a first high voltage power supply configured to apply a first voltage to said electron emitter; and

a second high voltage power supply configured to apply a second voltage to said target.

3. The compact x-ray generator as defined in claim 2, wherein:

said first high voltage is a negative voltage; and

said second high voltage is a positive voltage.

4. The compact x-ray generator as defined in claim 2, wherein:

at least one of said first high voltage power supply and said second high voltage power supply is a Cockcroft-Walton type voltage generator.

5. The compact x-ray generator as defined in claim 3, wherein:

the difference between said first high voltage and said second high voltage is greater than or equal to 250 kV.

6. The compact x-ray generator as defined in claim 4, wherein:

at least one of said first high voltage power supply and said second high voltage power supply is configured to fold in order to decrease the size of the x-ray generator.

7. The compact x-ray generator as defined in claim 1, further comprising:

an isolation transformer comprising one primary winding and at least two secondary windings providing voltage to said electron emitter and a grid.

8. A tool for determining at least one property of a formation surrounding a borehole comprising:

an x-ray generator comprising an electron emitter and a target, said x-ray generator being configured to generate an input radiation spectrum that passes into said formation;

a first high voltage power supply being configured to apply a first voltage to said electron emitter;

a second high voltage power supply being configured to apply a second voltage to said target;

a first radiation detector spaced a first distance from said target and being configured to detect radiation reflected by said formation and produce a first output signal;

a second radiation detector spaced a second distance from said target and being configured to detect radiation reflected by said formation and produce a second output signal;

an analysis unit being configured to determine at least one property of said formation using said first output signal and said second output signal.

9. The tool for determining at least one property of a formation surrounding a borehole as defined in claim 8, wherein:

said property is a density of said formation.

10. The tool for determining at least one property of a formation surrounding a borehole as defined in claim 8, wherein:

said property is a photoelectric factor of said formation.

11. The tool for determining at least one property of a formation surrounding a borehole as defined in claim 8, further comprising:

a reference radiation detector;

a filter positioned between said target and said reference radiation detector, said filter being configured to alter the input radiation spectrum;

said reference detector being configured to produce an output reference signal in response to incident radiation;

said analysis unit further being configured to control at least one of an acceleration voltage and a beam current of said x-ray generator based on said output reference signal.

12. The tool for determining at least one property of a formation surrounding a borehole as defined in claim 8, wherein;

said tool is housed in a sled;

said sled being configured to be lowered downhole and secured against a side wall of said borehole.

13. The tool for determining at least one property of a formation surrounding a borehole as defined in claim 8, wherein;

said electron emitter comprises a cathode and a grid;

14. The tool for determining at least one property of a formation surrounding a borehole as defined in claim 13, further comprising;

an isolation transformer providing a voltage to said electron emitter and said grid.

15. The tool for determining at least one property of a formation surrounding a borehole as defined in claim 8, wherein;

said first voltage is a negative voltage; and

said second voltage is a positive voltage.

16. The tool for determining at least one property of a formation surrounding a borehole as defined in claim 15, wherein;

the difference between said first voltage and said second voltage falls in the range of 250 kV-500 kV.

17. The tool for determining at least one property of a formation surrounding a borehole as defined in claim 8, wherein;

said first high voltage power supply and said second high voltage power supply are Cockcroft-Walton type voltage ladders.

18. A method for determining the density of a formation surrounding a borehole in a high temperature environment comprising the steps of:

providing an input radiation by an x-ray generator, said input radiation having energy at or above 250 keV;

detecting radiation passed through said formation at a first radiation detector;

detecting radiation passed through said formation as a second radiation detector; and

analyzing outputs of said first radiation detector and said second radiation detector to determine a density of said formation.

19. The method for determining the density of a formation surrounding a borehole in a high temperature environment as defined in claim 18, further comprising the steps of:

filtering said input radiation to create a reference radiation;

measuring said reference radiation at a reference radiation detector;

controlling at least one of a beam current and acceleration voltage of said x-ray generator based on an output of said reference radiation detector.

20. The method for determining the density of a formation surrounding a borehole in a high temperature environment as defined in claim 18, further comprising the steps of:

providing a high negative voltage to an electron emitter of said x-ray generator; and

providing a high positive voltage to a target of said x-ray generator;

wherein the difference between said high negative voltage and said high positive voltage is greater than or equal to 250 kV.

21. A method of stabilizing the output of an x-ray generator comprising:

filtering radiation produced by said x-ray generator to create a dual peak spectrum with a high energy region and a low energy region,

receiving said filtered radiation using a reference detector, and

using an output of said reference detector to modify at least one of current and voltage of electrical energy applied to said x-ray generator, thereby stabilizing said output of said x-ray generator.