Near-field sensitivity of formation and cement porosity measurements with radial resolution in a borehole
A neutron porosity tool having an electronic neutron generator arrangement and a control mechanism used to provide voltage and pulses to an electronic neutron tube is provided, the neutron generator arrangement including: at least one vacuum tube; at least one ion target; at least one radio-frequency cavity; at least one high-voltage generator; at least two neutron detectors; at least one pulser circuit; and at least one control circuit. A method of controlling a neutron porosity tool having an electronic neutron generator arrangement and a control mechanism that provides voltage, and pulses to an electronic neutron tube, the method including at least: controlling a bipolar neutron tube to produce two distinct neutron reactions; using a control circuit to modify the output of a pulser circuit; and using a plurality of neutron detectors to determine formation response offsets.
1. A neutron porosity tool comprising:
a first vacuum tube enclosing a first ion target, a target electrode coupled to the first ion target, a first radio-frequency (RF) cavity, and a first cathode;
a plurality of neutron detectors;
a current source coupled to the first cathode;
a first pulser circuit coupled to the first RF cavity and to the plurality of neutron detectors, the first pulser circuit to drive the first RF cavity and to gate a response of the plurality of detectors; and
a first high-voltage generator coupled to the target electrode, the first high-voltage generator to provide a voltage to the target electrode.
2. The tool of claim 1 , further comprising a second pulser circuit, wherein the first and second pulser circuits are to provide two differing ion accelerating voltages, such that deuterium-deuterium reactions and deuterium-tritium reactions are generated within a single reactance plane while the tool is positioned within a borehole.
3. The tool of claim 1 , further comprising a second pulser circuit, wherein the first and second pulser circuits are to provide substantially equivalent ion accelerating voltages, such that deuterium-deuterium reactions are generated within a single reactance plane while the tool is positioned within a borehole.
4. The tool of claim 1 , further comprising a second pulser circuit, wherein the first and second pulser circuits are to provide substantially equivalent ion accelerating voltages, such that deuterium-tritium reactions are generated within a single reactance plane while the tool is positioned within a borehole.
5. The tool of claim 1 , further comprising a second vacuum tube enclosing a second cathode and a second ion target co-located with the first ion target, wherein the target electrode is a common target electrode that is coupled to the first and second ion targets, and the first high-voltage generator is to provide the voltage to the common target electrode, such that deuterium-deuterium reactions and deuterium-tritium reactions are generated within a single reactance plane while the tool is positioned within a borehole.
6. The tool of claim 1 , wherein the plurality of detectors comprise helium-3 gas.
7. The tool of claim 1 , wherein the plurality of detectors comprise Lithium-6 glass.
8. The tool of claim 1 , further comprising:
a second vacuum tube that forms a conjoined tube with the first vacuum tube, wherein the second vacuum tube encloses a second ion target, a second RF cavity, and a second cathode, and the target electrode is a common target electrode that is coupled to the first and second ion targets.
9. The tool of claim 8 , further comprising:
a second pulser circuit coupled to the second RF cavity, wherein the first and second pulser circuits are coupled to a common ground potential, and the second pulser circuit is to drive the second RF cavity.
10. The tool of claim 9 , wherein the plurality of neutron detectors includes a first neutron detector and a second neutron detector, the first pulser circuit is to gate a response of the first neutron detector, and the second pulser circuit is to gate a response of the second neutron detector.
11. The tool of claim 9 , wherein the first pulser circuit operates in phase with the second pulser circuit.
12. The tool of claim 1 , further comprising:
a second high-voltage generator, wherein the first cathode is coupled between the second high-voltage generator and the current source.
13. A method of operating a neutron porosity tool, the method comprising:
causing a vacuum tube of the tool to produce two distinct neutron reactions by:
driving a first radio-frequency (RF) cavity with a first pulser circuit of the tool, and
providing a voltage to a target electrode with a first high-voltage generator of the tool, the vacuum tube enclosing the first RF cavity and the target electrode; and
gating a response of a plurality of neutron detectors with the first pulser circuit to determine formation response offsets.
14. The method of claim 13 , further comprising causing the first pulser circuit and a second pulser circuit of the tool to provide two differing ion accelerating voltages, such that deuterium-deuterium reactions and deuterium-tritium reactions are generated within a single reactance plane while the tool is positioned within a borehole.
15. The method of claim 13 , wherein the tool comprises a second vacuum tube enclosing a second cathode and a second ion target co-located with the first ion target, the target electrode is a common target electrode that is coupled to the first and second ion targets, and the method further comprising providing the voltage to the common target electrode with the first high-voltage generator, such that deuterium-deuterium and deuterium-tritium reactions are generated within a single reactance plane while the tool is positioned within a borehole.