A wireline or logging while drilling device includes: a first coil configured to vary the intensity of a main magnetic field so as to produce phase modulation of signals emitted by spins in a sensitive volume; and a second coil configured to excite the spins in the sensitive volume in an inverse ratio of gyromagnetic constants of the spins; and receive signals from the spins displaced in frequency from the Larmor frequency of the spins by the phase modulation produced by the first coil.

The invention relates to an NMR system, and more particularly to an NMR measurement unit including a flow channel for separating a sample from a fluid stream in a process channel, a magnet arranged relative to flow channel for creating a magnetic field in part of flow channel, a coil arranged relative to flow channel for exciting NMR active nuclei of the sample in flow channel and for receiving the frequency pulse that returns to coil from NMR active nuclei, a frame comprising a fastening flange for sealing NMR measurement unit to process channel and a chamber that is closed relative to fluid stream and connected to fastening flange, arranged to be installed mainly inside process channel, within which chamber magnet and coil are arranged and through which chamber the flow channel passes, the frame installable such that flow channel is positioned inside process channel.

A method for operating a nuclear magnetic flowmeter for determining the flow of a multi-phase medium flowing through a measuring tube that is suitable for media exhibiting phase slip with which the characterization of the gaseous phase is simplified, is achieved by a pulse spoiling the magnetization at least in the direction of the magnetic field or a pulse sequence spoiling the magnetization in the direction of the magnetic field being emitted by a coil-shaped antenna, particularly in combination with dephasing gradients, and then, after a waiting time t.sub.W, a nuclear magnetic measurement is carried out in that the medium is excited with excitation pulses by the coil-shaped antenna and the measuring signals generated by the excitation in the medium are detected.

A method for operating a nuclear magnetic flowmeter for determining the flow of a multi-phase medium flowing through a measuring tube that is suitable for media exhibiting phase slip with which the characterization of the gaseous phase is simplified, is achieved by a pulse spoiling the magnetization at least in the direction of the magnetic field or a pulse sequence spoiling the magnetization in the direction of the magnetic field being emitted by a coil-shaped antenna, particularly in combination with dephasing gradients, and then, after a waiting time t.sub.W, a nuclear magnetic measurement is carried out in that the medium is excited with excitation pulses by the coil-shaped antenna and the measuring signals generated by the excitation in the medium are detected.

This disclosure provides systems, methods, and apparatus for measuring flow in and around a borehole of an earth formation. A flow measurement device can include a magnet configured to generate a static solenoidal magnetic field with a field intensity that decreases in strength peripherally from the magnet, an electromagnet disposed around the magnet and configured to generate a time varying solenoidal magnetic field, and a radio frequency (RF) coil disposed around the magnet and configured to generate an RF magnetic field transverse to the static solenoidal magnetic field. The flow measurement device can calculate a flow velocity in and around the flow measurement device based upon a signal received by the RF coil.

This disclosure provides systems, methods, and apparatus for measuring flow in and around a borehole of an earth formation. A flow measurement device can include a magnet configured to generate a static solenoidal magnetic field with a field intensity that decreases in strength peripherally from the magnet, an electromagnet disposed around the magnet and configured to generate a time varying solenoidal magnetic field, and a radio frequency (RF) coil disposed around the magnet and configured to generate an RF magnetic field transverse to the static solenoidal magnetic field. The flow measurement device can calculate a flow velocity in and around the flow measurement device based upon a signal received by the RF coil.

A method for operating a nuclear-magnetic flowmeter in which, when determining a velocity of the medium through a measuring tube, the dependency on properties or the state of a medium is at least reduced. The method exciting a first volume of the magnetized medium flowing at a first velocity within a first measuring section to nuclear-magnetic resonances and a first signal sequence is formed characterizing the nuclear-magnetic resonances of the medium in the first volume, and then, exciting a second volume of the magnetized medium flowing at a second velocity within the first measuring section is excited to nuclear-magnetic resonances and a second signal sequence is formed characterizing the nuclear-magnetic resonances of the medium in the second volume. A quotient sequence is determined from each of the first and second signal sequences, and the first velocity and/or the second velocity is/are determined using the quotient sequence.

A method for operating a nuclear-magnetic flowmeter in which, when determining a velocity of the medium through a measuring tube, the dependency on properties or the state of a medium is at least reduced. The method exciting a first volume of the magnetized medium flowing at a first velocity within a first measuring section to nuclear-magnetic resonances and a first signal sequence is formed characterizing the nuclear-magnetic resonances of the medium in the first volume, and then, exciting a second volume of the magnetized medium flowing at a second velocity within the first measuring section is excited to nuclear-magnetic resonances and a second signal sequence is formed characterizing the nuclear-magnetic resonances of the medium in the second volume. A quotient sequence is determined from each of the first and second signal sequences, and the first velocity and/or the second velocity is/are determined using the quotient sequence.

A method for determining a pulse duration T.sub.90 of a 90 pulse in a nuclear magnetic measuring method. A signal generator has a known generator resistance R.sub.S, wherein a coil has a coil impedance Z.sub.L with a coil resistance R.sub.L and a coil reactance X.sub.L, wherein a coupling circuit has an adjustable matching capacitance C.sub.M and an adjustable tuning capacitance C.sub.T, and wherein the medium has a Larmor precession having an angular Larmor frequency .sub.P. The time needed for determining the pulse duration T.sub.90 of the 90 pulse is reduced by the matching capacitance C.sub.M and the tuning capacitance C.sub.T being set so that the angular resonance frequency .sub.0 corresponds to the angular Larmor frequency .sub.P and by power matching being present between the signal generator and the coil. The coil resistance R.sub.L is determined and the pulse duration T.sub.90 is determined as a function of the coil resistance R.sub.L.

A method for determining a pulse duration T.sub.90 of a 90 pulse in a nuclear magnetic measuring method. A signal generator has a known generator resistance R.sub.S, wherein a coil has a coil impedance Z.sub.L with a coil resistance R.sub.L and a coil reactance X.sub.L, wherein a coupling circuit has an adjustable matching capacitance C.sub.M and an adjustable tuning capacitance C.sub.T, and wherein the medium has a Larmor precession having an angular Larmor frequency .sub.P. The time needed for determining the pulse duration T.sub.90 of the 90 pulse is reduced by the matching capacitance C.sub.M and the tuning capacitance C.sub.T being set so that the angular resonance frequency .sub.0 corresponds to the angular Larmor frequency .sub.P and by power matching being present between the signal generator and the coil. The coil resistance R.sub.L is determined and the pulse duration T.sub.90 is determined as a function of the coil resistance R.sub.L.