Abstract: The present invention provides a novel use of a material having a high internal magnetostrictive damping and/or using material with explicitly low magnetostriction as an antenna core material for NMR and resistivity devices in a borehole. The probe stuctural geometry facilitates the use of material, which has a relatively low magnectic permeability.

Abstract: A transmitter antenna assembly for transient electromagnetic well logging instrument comprises an antenna coil coupled with a current source and a magnetic core having residual magnetization. Switching current in the antenna coil results in magnetization reversal in the magnetic core and change in magnetic dipole moment of the antenna. After the magnetization reversal is complete the current is removed and the new vector of magnetic dipole of the antenna maintains constant (steady-state phase of the antenna dipole) due to magnetic hysteresis of magnetic material employed for the magnetic core. No power expenditure during the steady-state phase of the magnetic dipole facilitates highly effective generation and fast switching of a large magnetic dipole. The magnetic core also serves as a shield between the antenna coil and any conductive part of the antenna assembly.

Abstract: Pulse sequences are applied to a fluid in an earth formation in a static magnetic field having internal gradients. From the received signals, relaxation and diffusion characteristics of the fluid are determined. The determination takes into account the internal field gradients.

Abstract: The present invention provides a novel use of a material having a high internal magnetostrictive damping and/or using material with explicitly low magnetostriction as a NMR probe core material. The probe structural geometry facilitates the use of material, which has a relatively low magnetic permeability.

Abstract: The invention is a method of reducing the effects of non-formation signals in an NMR logging echo signal obtained within a borehole in an earth formation. The method obtains a non-formation signal by the application of at least an excitation pulse, and preferably also at least one refocusing pulse. The obtained signal is used to numerically construct a synthetic ringing signal sequence. The constructed signal can then be subtracted from an NMR echo signal to reduce the effects of ringing.

Abstract: The present invention provides an improved NMR sequence for detecting small amount of a substance having short NMR transversal relaxation in the presence of a large amount of a substance having long NMR relaxation. A sequence of pulses enables the original z-oriented magnetization vector of a substance to experience differing reorientation effects based on the relative transverse relaxation rate of the substance. After said pulse sequence, a substance with long transverse relaxation experiences a substantial inversion of its nuclear magnetization vector, while a substance with short transverse relaxation experiences a nearly zero value of its vector. After a determinable wait time, said vectors can be shown to experience recognizably different behavior under the application of a CPMG sequence of pulses. Appropriate wait time can be determined by zeroing out spin echoes during the CPMG pulse sequence.

Abstract: A method is disclosed for analyzing body composition. The method includes inducing a static magnetic field in the body. The static magnetic field has a known distribution along a longitudinal axis of the body. A radio frequency magnetic field is induced in the body. The radio frequency and a bandwidth thereof are selected to induce nuclear magnetic resonance phenomena in a selected axial segment along the body. Nuclear magnetic resonance phenomena are from the selected axial segment. Composition is determined from the magnetic resonance signals. The measurement may be repeated in different axial segments by changing the static field amplitude or a frequency of the RF magnetic field. In some embodiments, a gradient field is superimposed over the static field.

Abstract: The present invention provides a novel use of a material having a high internal magnetostrictive damping and/ or using material with explicitly low magnetostriction as a NMR probe core material. The probe structural geometry facilitates the use of material, which has a relatively low magnetic permeability.

Abstract: A method is disclosed for measuring whole body composition. The method includes confining movement of the body to a selected volume, inducing a static magnetic field in the volume, inducing a pulsed radio frequency magnetic field in the volume, and receiving nuclear magnetic resonance signals from the body. The resonance signals from any part of the body are substantially independent of a position of the body part within the volume. Whole body composition is assessed from the resonance signals.

Abstract: The present invention provides an improved NMR sequence for detecting small amount of a substance having short NM transversal relaxation in the presence of a large amount of a substance having long NMR relaxation. A sequence of pulses enables the original z-oriented magnetization vector of a substance to experience differing reorientation effects based on the relative transverse relaxation rate of the substance. After said pulse sequence, a substance with long transverse relaxation experiences a substantial inversion of its nuclear magnetization vector, while a substance with short transverse relaxation experiences a nearly zero value of its vector. After a determinable wait time, said vectors can be shown to experience recognizably different behavior under the application of a CPMG sequence of pulses. Appropriate wait time can be determined by zeroing out spin echoes during the CPMG pulse sequence.

Abstract: The invention is a method of reducing the effects of non-formation signals in an NMR logging echo signal obtained within a borehole in an earth formation. The method obtains a non-formation signal by the application of at least an excitation pulse, and preferably also at least one refocusing pulse. The obtained signal is used to numerically construct a synthetic ringing signal sequence. The constructed signal can then be subtracted from an NMR echo signal to reduce the effects of ringing.

Abstract: A method for acquiring nuclear magnetic resonance measurements of a material uses a modified CPMG sequence with a refocusing pulse having a tipping angle less than 180 °. The results of using the shortened refocusing pulse with reduced power requirements are comparable to those obtained with a conventional CPMG sequence.

Abstract: Pulse shaping is used for reducing the interference between echo trains of multiple frequency NMR logging applications in a gradient logging tool. The major contribution to the interference between different logging sequences comes from the sidelobes in the spectra of the excitation signal caused by modulating the RF signal with a square pulse. By shaping the tipping pulse in a CPMG pulse sequence, the interference between logging sequences at proximate frequencies is reduced. The shaped pulse may be a smooth function such as the Chebyshev function or it may be a composite of two rectangular pulses. In an alternate embodiment of the invention, the refocusing pulses are also shaped.

Abstract: A side-looking NMR logging tool incorporates a permanent magnet arrangement having a magnetization direction oriented towards a side of the tool and a dipole RF antenna displaced towards the front of the tool. The magnet arrangement produces a shaped region of investigation in front of the tool wherein the magnetic field has a uniform field strength and the RF field has a uniform field strength in a direction orthogonal to the static field. The shaping of the static field is accomplished by the magnet arrangement comprising a plurality of magnets having parallel magnetization or by a single shaped magnet. The antenna arrangement includes a gapped core made of non-ferritic soft material for increasing the antenna efficiency. The magnet arrangement also reduces ringing in the core and the antenna. An optional RF shield is used to reduce NMR signals from borehole fluids.

Abstract: A method for acquiring nuclear magnetic resonance measurements of a material uses a gradient tool. A modified CPMG sequence is used wherein the duration of the refocusing pulse is selected to maximize the SNR of the pulse echoes relative to a standard CPMG sequence in which the refocusing pulse has twice the duration of the tipping pulse. The results of using the shortened refocusing pulse with reduced power requirements are comparable to those obtained with a conventional CPMG sequence.

Abstract: The present invention provides a novel use of a material having a high internal magnetostrictive damping and/ or using material with explicitly low magnetostriction as a NMR probe core material. The probe structural geometry facilitates the use of material, which has a relatively low magnetic permeability.

Abstract: The invention is a method and apparatus for performing NMR measurements in MWD effective for large and small boreholes. The invention uses a magnet assembly to produce a generally oval static magnetic field. The invention also employs an antenna assembly comprised of a primary and secondary antenna to deliver a sequence of RF magnetic pulses. For small holes, the antenna assembly operates to substantially match the iso-lines of the static magnetic field within the rock formation during a transmission pulse. For large holes, the invention works in a side-looking mode and the antenna assembly operates both to match the iso-lines of the static magnetic field within the rock formation and to diminish the magnetic field within the borehole during a transmission pulse. The secondary antenna can also be used as a receiver of spin echo signals, or optionally, to make adjustments to the received signal.

Abstract: The invention is a method and apparatus for performing NMR measurements in MWD effective for large and small boreholes. The invention uses a magnet assembly to produce a generally oval static magnetic field. The invention also employs an antenna assembly comprised of a primary and secondary antenna to deliver a sequence of RF magnetic pulses. For small holes, the antenna assembly operates to substantially match the iso-lines of the static magnetic field within the rock formation during a transmission pulse. For large holes, the invention works in a side-looking mode and the antenna assembly operates both to match the iso-lines of the static magnetic field within the rock formation and to diminish the magnetic field within the borehole during a transmission pulse. The secondary antenna can also be used as a receiver of spin echo signals, or optionally, to make adjustments to the received signal.

Abstract: The present invention provides a novel use of a powdered high saturation flux density soft magnetic material as a NMR probe core material. The probe structural geometry facilitates the use of powdered material, which has a relatively low magnetic permeability.

Abstract: A side-looking NMR logging tool incorporates a permanent magnet arrangement having a magnetization direction oriented towards a side of the tool and a dipole RE antenna displaced towards the front of the tool. The magnet arrangement produces a shaped region of investigation in front of the tool wherein the magnetic field has a uniform field strength and the RF field has a uniform field strength in a direction orthogonal to the static field. The shaping of the static field is accomplished by the magnet arrangement comprising a plurality of magnets having parallel magnetization or by a single shaped magnet. The antenna arrangement includes a gapped core made of non-ferritic soft material for increasing the antenna efficiency. The magnet arrangement also reduces ringing in the core and the antenna. An optional RF shield is used to reduce NMR signals from borehole fluids.