Nuclear magnetic resonance logging tool with quadrature coil configuration
First Claim
1. A method comprising:
- introducing a nuclear magnetic resonance (NMR) logging tool into a wellbore penetrating a subterranean formation, the wellbore containing a fluid and having a z-axis extending along a length of the wellbore, wherein the NMR logging tool has a z-coil and a transversal coil;
generating in a volume of investigation of the subterranean formation either (1) a transversal radiofrequency (RF) excitation in a transversal direction relative to the z-axis of the wellbore with the transversal coil or (2) a quadrature RF excitation with both the z-coil and the transversal coil, wherein a selection between the transversal RF excitation and the quadrature RF excitation is based on a resistivity of the fluid, a diameter of the wellbore, a depth into the subterranean formation of the volume of investigation, or a combination thereof; and
detecting an NMR signal from the subterranean formation produced as a result of the transversal RF excitation or the quadrature RF excitation with one of;
(1) the transversal coil or (2) both the z-coil and the transversal coil.
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Accused Products
Abstract
Nuclear magnetic resonance (NMR) logging tools may be configured for situation-dependent NMR logging operations by including two dissimilar coils that may function in four different modes of operation based on logging conditions including: a resistivity of the fluid, a diameter of the wellbore, a depth into the subterranean formation of the volume of investigation, or a combination thereof. For example, an NMR logging tool with a z-coil and a transversal coil may be useful in generating in a volume of investigation of a subterranean formation either (1) a transversal radiofrequency (RF) excitation with the transversal coil or (2) a quadrature RF excitation with both the z-coil and the transversal coil, where the choice of transversal or quadrature RF excitation is based on the logging conditions; and detecting an NMR signal from the subterranean formation with one of: (1) the transversal coil or (2) both the z-coil and the transversal coil.
14 Citations
24 Claims
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1. A method comprising:
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introducing a nuclear magnetic resonance (NMR) logging tool into a wellbore penetrating a subterranean formation, the wellbore containing a fluid and having a z-axis extending along a length of the wellbore, wherein the NMR logging tool has a z-coil and a transversal coil; generating in a volume of investigation of the subterranean formation either (1) a transversal radiofrequency (RF) excitation in a transversal direction relative to the z-axis of the wellbore with the transversal coil or (2) a quadrature RF excitation with both the z-coil and the transversal coil, wherein a selection between the transversal RF excitation and the quadrature RF excitation is based on a resistivity of the fluid, a diameter of the wellbore, a depth into the subterranean formation of the volume of investigation, or a combination thereof; and detecting an NMR signal from the subterranean formation produced as a result of the transversal RF excitation or the quadrature RF excitation with one of;
(1) the transversal coil or (2) both the z-coil and the transversal coil. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method comprising:
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introducing a nuclear magnetic resonance (NMR) logging tool into a wellbore penetrating a subterranean formation, the wellbore containing a fluid and having a z-axis extending along a length of the wellbore, wherein the NMR logging tool has a z-coil and a transversal coil; generating a plurality of radiofrequency (RF) excitations each corresponding to different volumes of interest in the subterranean formation, wherein the plurality of RF excitations includes a transversal RF excitation in a transversal direction relative to the z-axis of the wellbore with the transversal coil and a quadrature RF excitation with the z-coil and the transversal coil, wherein a frequency corresponding to the quadrature RF excitation is less than a frequency corresponding to the transversal RF excitation; and detecting an NMR signal from the subterranean formation produced as a result of the transversal RF excitation or the quadrature RF excitation with one of;
(1) the transversal coil or (2) both the z-coil and the transversal coil. - View Dependent Claims (11, 12, 13, 14)
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15. A method comprising:
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introducing a nuclear magnetic resonance (NMR) logging tool into a wellbore penetrating a subterranean formation, the wellbore containing an oil-based mud (OBM) and having a z-axis extending along a length of the wellbore, wherein the NMR logging tool having a transversal dipole magnet, a z-coil, and a transversal coil; generating a quadrature radiofrequency (RF) excitation with the z-coil and the transversal coil; generating a transversal RF excitation in a transversal direction relative to the z-axis of the wellbore with the transversal coil; detecting a first NMR signal and a second NMR signal from the subterranean formation produced by the quadrature RF excitation and the transversal RF excitation, respectively, with one of;
(1) the transversal coil or (2) both the z-coil and the transversal coil;calculating a quality factor for each of the z-coil and the transversal coil based on the first and second NMR signals relative to the quadrature RF excitation and the transversal RF excitation, respectively; and calculating a formation anisotropy based on the quality factor for the z-coil and the quality factor for the transversal coil. - View Dependent Claims (16, 17)
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18. A system comprising:
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a wellbore penetrating a subterranean formation containing a fluid and having a z-axis extending along a length of the wellbore; and a nuclear magnetic resonance (NMR) logging tool extendable within the wellbore and having a z-coil and a transversal coil, wherein the NMR logging tool generates in a volume of investigation of the subterranean formation either (1) a transversal radiofrequency (RF) excitation in a transversal direction relative to the z-axis of the wellbore with the transversal coil or (2) a quadrature RF excitation with both the z-coil and the transversal coil, a selection between the transversal RF excitation and the quadrature RF excitation being based on a resistivity of the fluid, a diameter of the wellbore, a depth into the subterranean formation of the volume of investigation, or a combination thereof, and wherein the NMR logging tool detects an NMR signal from the subterranean formation produced as a result of the transversal RF excitation or the quadrature RF excitation with one of the transversal coil or both the z-coil and the transversal coil. - View Dependent Claims (19, 20, 21, 22, 23, 24)
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Specification