Well logging apparatus and method for measuring formation properties
First Claim
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1. A logging tool comprising:
- an elongated body having a longitudinal axis;
a neutron source housed within the elongated body;
a gamma ray detector housed within the elongated body and positioned longitudinally to one end of the neutron source; and
a neutron detector housed within the elongated body positioned along one side of the neutron source.
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Abstract
A logging tool includes an elongated body housing a neutron source and at least one neutron detector positioned along one side of the neutron source. Some embodiments of the logging tool include at least one gamma ray detector longitudinally separated from and to one end of the neutron source, and may be used to make simultaneous gamma ray and neutron logging measurements. In some embodiments, the logging tool also includes a (n, 2n)-neutron shield positioned to one end of the neutron detector, longitudinally between the neutron detector and the neutron source.
74 Citations
57 Claims
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1. A logging tool comprising:
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an elongated body having a longitudinal axis;
a neutron source housed within the elongated body;
a gamma ray detector housed within the elongated body and positioned longitudinally to one end of the neutron source; and
a neutron detector housed within the elongated body positioned along one side of the neutron source. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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17. A logging tool comprising:
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an elongated body having a first section longitudinally separated from a second section;
at least one gamma ray detector housed within the first section;
an accelerator neutron source housed within the second section, the accelerator neutron source having a target;
a first plurality of neutron detectors housed within the second section, the first plurality being positioned along one side of the neutron source and at a first longitudinal distance from the target; and
a second plurality of neutron detectors housed within the second section, the second plurality being positioned along the one side of the neutron source and at a second longitudinal distance greater than the first longitudinal distance from the target.
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30. A logging tool moveable within a borehole comprising an elongated body having a longitudinal axis and housing therein:
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a neutron source;
a first neutron detector;
a second neutron detector positioned towards one end of the first neutron detector; and
a (n, 2n)-neutron shield positioned longitudinally between the neutron source and the first neutron detector, wherein the neutron source is radially offset from the longitudinal axis to form a gap between the neutron source and an inner surface to one side of the elongated body, and the (n, 2n)-neutron shield, the first neutron detector and the second neutron detector are positioned in the gap along side the neutron source. - View Dependent Claims (31, 32, 33, 34, 35, 36, 37, 39, 40)
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38. A logging tool moveable within a borehole that traverses a subsurface formation comprising:
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an elongated body having a longitudinal axis;
a neutron source housed within the elongated body, the neutron source being radially offset from the longitudinal axis to form a gap between the neutron source and one side of the elongated body;
a neutron detector positioned in the gap along side the neutron source; and
a neutron source monitor positioned adjacent to the neutron source within the elongated body.
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41. A method of evaluating a subsurface formation comprising:
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a) introducing a logging tool into a borehole that traverses the subsurface formation, the logging tool comprising;
an elongated body having a longitudinal axis;
a neutron source housed within the elongated body;
at least one gamma ray detector housed within the elongated body and positioned longitudinally to one end of the neutron source; and
at least one neutron detector housed within the elongated body and positioned along one side of the neutron source;
b) irradiating the subsurface formation with neutrons from the neutron source, the neutrons interacting with the subsurface formation to produce gamma rays and lower energy neutrons;
c) detecting the gamma rays and lower energy neutrons from the formation; and
d) analyzing the detected neutrons and gamma rays to evaluate the subsurface formation. - View Dependent Claims (42, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53)
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49. A method of evaluating a subsurface formation comprising:
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a) introducing a logging tool through a borehole that traverses the subsurface formation, the logging tool housing a neutron source, at least one neutron detector, and at least one gamma ray detector;
b) emitting a plurality of neutron bursts from the neutron source, the neutron bursts being separated by a first time interval;
c) detecting neutrons from the formation with the neutron detector and detecting gamma rays from the formation with the gamma ray detector during the first time interval between neutron bursts;
d) after the last of the plurality of neutron bursts, detecting neutrons from the formation with the neutron detector and gamma rays from the formation with the gamma ray detector during a second time interval; and
f) analyzing the neutrons and gamma rays detected in steps c) and d) to determine at least one of the following;
slowing-down-time (SDT), an elemental concentration, hydrogen index, borehole sigma, and formation sigma.
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54. A method of evaluating a subsurface formation comprising:
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a) introducing a logging tool into a borehole that traverses the formation;
b) irradiating the formation with a burst of neutrons;
c) detecting gamma rays from the formation using one detector at two different time intervals relative to the neutron burst; and
d) calculating a neutron capture cross section indicative of the formation using the gamma rays detected using the one detector. - View Dependent Claims (55, 57)
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56. A method of evaluating a subsurface formation comprising:
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a) introducing a logging tool into a borehole that traverses the subsurface formation, the logging tool housing at least a neutron source, a neutron detector positioned along side the neutron source, and a (n, 2n)-neutron shield along side the neutron source and longitudinally between the neutron source and the neutron detector;
b) irradiating the formation with neutrons from the neutron source;
c) detecting neutrons from the formation;
d) analyzing the detected neutrons to determine a characteristic of the formation.
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Specification