Abstract: Core samples may been collected in a subterranean formation, preserved downhole in a pressurized nuclear magnetic resonance (NMR) core holder (1) comprising components for NMR imaging and (2) capable of maintaining the core samples at downhole fluid saturation state. For example, a pressurized NMR core holder may comprise a housing capable of containing downhole fluid pressures; a coil holder lining an inside of the housing and defining a core chamber; and one or more NMR coils maintained in a longitudinal position along the housing by the coil holder. Further, a system for performing the NMR imaging may comprise: a holder that maintains a pressurized NMR core holder in a desired position; and one or more magnets that are longitudinally movable along the pressurized NMR core holder.

Abstract: A side-looking Nuclear Magnetic Resonance (“NMR”) logging tool is designed to reduce and/or eliminate a borehole signal. The flipping angle of an RF refocusing pulse or excitation pulse emitted by the logging tool is manipulated to reduce the borehole signal.

Abstract: A side-looking Nuclear Magnetic Resonance (“NMR”) logging tool is designed to reduce and/or eliminate a borehole signal. The logging tool includes a magnetic assembly and a radio frequency (“RF”) transceiver antenna. The axial extent of the RF transceiver antenna has a length selected to reduce a borehole signal.

Abstract: A method includes disposing a downhole tool having a magnet assembly into a wellbore. The method includes generating, using the magnet assembly, a magnetic polarization in a volume into a subterranean region about the wellbore. The method also includes emitting an excitation in the magnetic polarization in the volume in the subterranean region. The method includes detecting, by at least one antenna, a nuclear magnetic resonance response to the excitation of the volume in the subterranean region. The method also includes determining a property of the subterranean region based on the nuclear magnetic resonance response.

Abstract: In some aspects of what is described here, a downhole nuclear magnetic resonance (NMR) logging tool can obtain NMR data from a subterranean region. The NMR logging tool includes a magnet assembly operable to produce a static magnetic field in the subterranean region. The NMR logging tool includes an antenna system having a first radio-frequency (RF) antenna, a second RF antenna, and a switching system. The switching system can switch the second antenna among operating modes while the NMR logging tool is disposed in a borehole in the subterranean region. The operating modes can include a booster mode, a spoiler mode, and an inactive mode.

Abstract: A side-looking Nuclear Magnetic Resonance (“NMR”) logging tool is designed to reduce and/or eliminate a borehole signal. The logging tool includes a magnet assembly having at least two magnets with magnetizations in different directions, thus resulting in a net magnetization that reduces the borehole signal.

Abstract: Apparatus and systems include a magnet assembly comprising a central magnet having a first axial end and a second, opposite axial end; a first end piece magnet having a proximal end and a distal end, the proximal end spaced apart from the first axial end of the central magnet; and a second end piece magnet spaced apart from the second axial end of the central magnet; at least one first shim magnet disposed adjacent to or at least partially surrounded by first magnetically permeable material, the at least one first shim magnet disposed next to an end of the first end piece magnet that is proximal to the central magnet, or next to an end of the first end piece magnet that is distal to the central magnet; and a downhole tool attached to the magnet assembly. Additional apparatus, systems, and methods are disclosed.

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.

Abstract: In accordance with embodiments of the present disclosure, a nuclear magnetic resonance (NMR) logging tool for use in wellbore logging operations is provided. The NMR logging tool features a three-part permanent magnet arrangement that reduces the attractive force between the NMR tool and casing, allowing the NMR tool to be lowered through wellbores of any size. Additionally, the disclosed arrangement of permanent magnets in the NMR tool may facilitate an effective pre-polarization of portions of the formation at different logging speeds. Further, the disclosed arrangement of permanent magnets in the NMR tool may provide a uniform or substantially uniform static magnetic field within the antenna window of the radio frequency (RF) antenna used to perform the measurements. The second magnet may be positioned between the first and third magnets in a longitudinal direction along the NMR tool, and a radio frequency (RF) antenna may be disposed adjacent the first magnet.

Abstract: Logging-while-drilling (LWD) tools may include multiple instruments interleaved into a compact configuration in a single drill string section that may be capable of nuclear magnetic resonance, resistivity, porosity, gamma density measurements, or any combination thereof. For example, a LWD tool may include a drill collar section containing: a nuclear magnetic resonance (NMR) electronics module and an NMR sensor module interleaved with a nuclear source and at least one nuclear detector.

Abstract: Systems, methods, and software for estimating the viscosity of a subterranean fluid based on NMR logging data are described. In some aspects, a viscosity model relates subterranean fluid viscosity to apparent hydrogen index. An apparent hydrogen index value for a subterranean region is computed based on nuclear magnetic resonance (NMR) logging data acquired from a subterranean region. A subterranean fluid viscosity value is computed for the subterranean region based on the viscosity model and the apparent hydrogen index value.

Abstract: A nuclear magnetic resonance (NMR) sensor including a magnet that generates a static magnetic field, a soft magnetic core secured to the magnet, and an antenna extending at least partially about the soft magnetic core and generating a radio frequency (RF) magnetic field. A magnetic permeability of the soft magnetic core in a direction of the static magnetic field is less than the magnetic permeability of the soft magnetic core in a direction of the RF magnetic field.

Abstract: Apparatus and systems include a magnet assembly comprising a central magnet having a first axial end and a second, opposite axial end; a first end piece magnet having a proximal end and a distal end, the proximal end spaced apart from the first axial end of the central magnet; and a second end piece magnet spaced apart from the second axial end of the central magnet; at least one first shim magnet disposed adjacent to or at least partially surrounded by first magnetically permeable material, the at least one first shim magnet disposed next to an end of the first end piece magnet that is proximal to the central magnet, or next to an end of the first end piece magnet that is distal to the central magnet; and a downhole tool attached to the magnet assembly. Additional apparatus, systems, and methods are disclosed.

Abstract: In some aspects of what is described here, a downhole nuclear magnetic resonance (NMR) logging tool can obtain NMR data from a subterranean region. The NMR logging tool includes a magnet assembly operable to produce a static magnetic field in the subterranean region. The NMR logging tool includes an antenna system having a first radio-frequency (RF) antenna, a second RF antenna, and a switching system. The switching system can switch the second antenna among operating modes while the NMR logging tool is disposed in a borehole in the subterranean region. The operating modes can include a booster mode, a spoiler mode, and an inactive mode.

Abstract: A nuclear magnetic resonance (NMR) logging method includes providing a hybrid pulse sequence having a saturation pulse, an inversion pulse, and a detection sequence. The method also includes measuring echo signals in response to the hybrid pulse sequence. The method also includes deriving a spin-lattice time constant (T1) distribution from the measured echo signals. A NMR system includes a hybrid pulse sequence module to provide a hybrid pulse sequence with a saturation pulse, an inversion pulse, and a detection sequence. The NMR system also includes a control module to select a time interval between the saturation pulse and the inversion pulse.

Abstract: A method and apparatus for estimating a flow rate of a phase of a multiphase fluid is disclosed. A first velocity distribution is obtained for a first set of nuclei in the fluid from a Nuclear Magnetic Resonance (NMR) signal received for the fluid in response to a first NMR excitation signal. A second velocity distribution is obtained for a second set of nuclei in the fluid from an NMR signal received for the fluid in response to a second NMR excitation signal. A velocity of the phase is estimated from the first velocity distribution and the second velocity distribution. The flow rate of the phase is estimated using the estimated velocity of the phase and an estimated volume fraction of the phase.

Abstract: A method and apparatus for estimating a flow rate of a phase of a multiphase fluid is disclosed. In the first method, nuclei in the fluid are polarized over two distances and a measured magnetization gives the relative fraction of two components of the fluid for a selected velocity. In the second method, nuclei in the fluid are polarized over a specified distance and measurements of the decay of spin echo signals is used to give the relative fraction of two components of the fluid for the selected velocity.

Abstract: A method for estimating a property of an earth formation includes: conveying a carrier through a borehole penetrating the earth formation; performing nuclear magnetic resonance (NMR) measurements on a sensitive volume in the formation using an NMR tool disposed at the carrier to provide a distribution of relaxation times; identifying peaks in the distribution of relaxation times; selecting at least one peak based on a characteristic of the at least one peak; and estimating the property using a relaxation time associated with the at least one peak.

Abstract: Pulse sequences are applied to a fluid in an earth formation with an external static magnetic field and NMR spin echo signals are obtained. The received NMR signals are affected by internal field gradients due to a contrast in magnetic susceptibility between the grains of the formation matrix and the fluid in the pore space. Processing of the data gives the relaxation time and diffusivity of the fluid.

Abstract: A method and apparatus for estimating a flow rate of a phase of a multiphase fluid is disclosed. A first velocity distribution is obtained for a first set of nuclei in the fluid from a Nuclear Magnetic Resonance (NMR) signal received for the fluid in response to a first NMR excitation signal. A second velocity distribution is obtained for a second set of nuclei in the fluid from an NMR signal received for the fluid in response to a second NMR excitation signal. A velocity of the phase is estimated from the first velocity distribution and the second velocity distribution. The flow rate of the phase is estimated using the estimated velocity of the phase and an estimated volume fraction of the phase.