Amplitude and/or phase modulated NMR pulse sequences
AssigneeBaker Hughes Incorporated
InventorsThomas Kruspe, Martin Blanz, Peter Rottengatter
Life of this patent
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Abstract
The excitation and/or refocusing pulses used in a CPMG sequence have a nonlinear phase and an envelope with no zero crossings and a corresponding frequency spectrum with sidelobes suppressed. As a result of this, peak power requirements are reduced. Pulse shaping is used for reducing the peak power requirements of a NMR logging tool.
Claims17
A method for determining a parameter of interest of a volume of an earth formation surrounding a borehole with a logging tool conveyed in the borehole, the method comprising:
- (a) using a magnet assembly on the logging tool to produce a static magnetic field in said formation;
- (b) producing a radio frequency (RF) magnetic field in said volume of the formation with an antenna on the logging tool, said RF magnetic field having a direction substantially orthogonal to a direction of the static field, the RF field having a carrier frequency related to an intensity of the static field in said volume, said RF field modulated by a pulse sequence comprising an excitation pulse and a plurality of refocusing pulses;
- and
- (c) measuring with the logging tool spin echo signals induced by the RF field in the formation;
- wherein a phase of at least one of said plurality of refocusing pulses varies nonlinearly with frequency.
A method for determining a parameter of interest of an earth formation surrounding a borehole with a logging tool conveyed in the borehole, the method comprising:
- (a) using a magnet assembly on the logging tool to produce a static magnetic field in said formation;
- (b) producing a first and a second radio frequency (RF) magnetic field in a first and second volume of the formation respectively with an antenna on thy logging tool, each of said RE magnetic fields having a direction substantially orthogonal to a direction of the static field, the RF field having a first and a second carrier frequency related to an intensity of the static field in said first and second volumes, each of said RF fields modulated by a pulse sequence comprising an excitation pulse and a plurality of refocusing pulses
- (c) measuring with the logging tool spin echo signals induced by the RE fields in the formation;
- wherein a phase of at least one of said plurality of refocusing pulses for each of said RF fields varies nonlinearly with frequency.
A method for determining a parameter of interest of a volume of earth formation surrounding a borehole with a logging tool conveyed in the borehole, the method comprising:
- (a) using a magnet assembly on the logging tool to produce a static magnetic field in said volume of the formation;
- (b) producing a radio frequency (RF) magnetic field in said volume of the formation with an antenna on the logging tool, said RE magnetic field having a direction substantially orthogonal to a direction of the static field, the RF field having a carrier frequency related to an intensity of the static field in said volume,
- (c) using a single side band mixer for modulating said RF field by a pulse sequence comprising an excitation pulse and a plurality of refocusing pulses and wherein a phase of at least one of said plurality of refocusing pulses varies nonlinearly with frequency;
- and
- (d) measuring with the logging tool spin echo signals induced by the RF field in the formation.
Dependencies are inferred from the claim text.