Abstract: A nuclear magnetic resonance (NMR) logging tool assembly method that employs rotational indexing to optimize the sensing volume. At least some embodiments include establishing an initial arrangement of the permanent magnets and marking each magnet to indicate their relative rotational orientations in the initial arrangement. Thereafter a series of magnetic field measurements and individual magnet rotations are performed to improve the uniformity of the magnetic field in the sensing volume. Once a satisfactory arrangement has been found, the magnets may be secured together and an antenna array installed along with the electronics for performing relaxation time measurements and providing logs of formation properties that can be derived therefrom, such as porosity, permeability, density, rock type, fluid type, etc. The tool may be packaged as a wireline sonde, a tubing-conveyed logging tool, or a logging while drilling (LWD) tool.

Abstract: Various disclosed nuclear magnetic resonance (NMR) logging systems and methods employ an array of antennas to provide increased resolution without sacrificing signal-to-noise ratio. Certain method embodiments include: establishing a static magnetic field (B0) with a tool moving along a borehole through a formation; concurrently driving a multiple antenna cells to produce a radio frequency field (B1) in said formation; measuring an individual response from each antenna cell as nuclear spins undergo precession in the formation; and determining at least one characteristic relaxation time of the formation based at least in part on the individual response. The individual responses can be associated with positions where the individual responses were measured, and the relaxation time can be determined from a combination of those responses associated with a given position. Certain responses may be excluded due to tool motion that degrades the measured response.

Abstract: A nuclear magnetic resonance (NMR) logging tool assembly method that employs rotational indexing to optimize the sensing volume. At least some embodiments include establishing an initial arrangement of the permanent magnets and marking each magnet to indicate their relative rotational orientations in the initial arrangement. Thereafter a series of magnetic field measurements and individual magnet rotations are performed to improve uniformity of the magnetic field in the sensing volume. Once a satisfactory arrangement has been found, the magnets may be secured together and an antenna array installed along with the electronics for performing relaxation time measurements and providing logs of formation properties that can be derived therefrom, such as porosity, permeability, density, rock type, fluid type, etc. The tool may be packaged as a wireline sonde, a tubing-conveyed logging tool, or a logging while drilling (LWD) tool.

Abstract: Various disclosed nuclear magnetic resonance (NMR) logging systems and methods employ an array of antennas to provide increased resolution without sacrificing signal-to-noise ratio. Certain method embodiments include: establishing a static magnetic field (B0) with a tool moving along a borehole through a formation; concurrently driving a multiple antenna cells to produce a radio frequency field (B1) in said formation; measuring an individual response from each antenna cell as nuclear spins undergo precession in the formation; and determining at least one characteristic relaxation time of the formation based at least in part on the individual response. The individual responses can be associated with positions where the individual responses were measured, and the relaxation time can be determined from a combination of those responses associated with a given position. Certain responses may be excluded due to tool motion that degrades the measured response.