Systems and methods for deep-looking NMR logging
First Claim
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1. A system for nuclear magnetic resonance (NMR) logging of an underground formation traversed by a borehole, the system having a longitudinal axis and comprising:
- two magnets polarized along the longitudinal axis, the magnets having like poles facing each other to generate in the underground formation a static magnetic field azimuthally symmetric with respect to the longitudinal axis, at least one of the facing magnetic poles being extended by one or more pole pieces with high permeability; and
an antenna assembly interposed between the two facing magnetic poles, the antenna assembly comprising one or more directional antenna segments capable of operating at multiple frequencies, each antenna segment generating oscillating radio frequency (RF) fields orthogonal to the static magnetic field in one or more azimuthally focused sections of the underground formation surrounding the borehole.
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Abstract
An NMR logging tool for conducting NMR measurements in a plurality of sensitive volumes ranging up to a meter from the tool. The tool comprises a magnetic assembly using one or more permanent magnets and at least one pole piece for extending a magnet pole and shaping the magnetic field to simulate a magnetic monopole in a sensitive volume within the formation. Different embodiments of a segmented antenna enable directional NMR logging. The tool embodiments and methods of their use are suitable for wireline or LWD logging, and can be used for directional drilling.
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Citations
15 Claims
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1. A system for nuclear magnetic resonance (NMR) logging of an underground formation traversed by a borehole, the system having a longitudinal axis and comprising:
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two magnets polarized along the longitudinal axis, the magnets having like poles facing each other to generate in the underground formation a static magnetic field azimuthally symmetric with respect to the longitudinal axis, at least one of the facing magnetic poles being extended by one or more pole pieces with high permeability; and an antenna assembly interposed between the two facing magnetic poles, the antenna assembly comprising one or more directional antenna segments capable of operating at multiple frequencies, each antenna segment generating oscillating radio frequency (RF) fields orthogonal to the static magnetic field in one or more azimuthally focused sections of the underground formation surrounding the borehole. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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Specification