Schlumberger Technology Corporation

Bruno Luong

Martin E Poitzsch

Krishnamurthy Ganesan

Peter Speier

Ralf Heidler

Steven F Crary

Roger A Dworak

The present invention is directed to a nuclear magnetic resonance apparatus and method for generating an axisymmetric magnetic field having long, straight contour lines in the resonance region. A magnetically permeable member is used to shape the static magnetic field generated by an array of permanent magnets. The magnetically permeable member minimizes variations of the static magnetic field in the formation due to vertical motion of the apparatus while obtaining a nuclear magnetic resonance measurement. Further, the magnetically permeable member may minimize variations of the static magnetic field in the formation due to lateral motion of the apparatus while obtaining a nuclear magnetic resonance measurement.

Method and apparatus for generating an axisymmetric magnetic field

An NMR measurement apparatus includes at least one magnet, at least one antenna, an RF pulse transmitter and a controller. The magnets) establish a static magnetic field, and the RF pulse transmitter is coupled to the antenna(e). The controller is coupled to the transmitter and the antenna(e). The controller is adapted to cause the RF transmitter to transmit RF pulse sequences into a sample and for each different RF pulse sequence, vary an estimated pulse width for producing a predetermined flip angle by a different scaling factor to produce flip angles near the predetermined flip angle. The controller is adapted to receive spin echo signals in response to the transmission of the RF pulse sequences; determine a property of the sample in response to the spin echo signals; and use the spin echo signals to determine an optimal pulse width for producing the predetermined flip angle.

Optimizing characteristics of RF pulses used in NMR measurements

Nuclear magnetic resonance apparatus and method for generating an axisymmetric magnetic field having straight contour lines in the resonance region

The present invention relates generally to an apparatus and method for obtaining an azimuthally resolved nuclear magnetic resonance measurement of an earth formation traversed by a borehole. The measurement can be made while drilling or using a wireline tool. At least one gradient coil is positioned circumferentially around the tool. A magnetic field is produced by the coil in a region of the formation facing the coil. The magnetic field is substantially parallel to the static magnetic field produced by a pair of permanent magnets which form a part of the tool. The additional field causes an additional phase shift for spins located in the region so that the spins subjected to the additional field do not form a spin-echo.

Nuclear magnetic resonance logging with azimuthal resolution using gradient coils

The present invention is directed to a nuclear magnetic resonance logging-while-drilling tool. The tool comprises a drill bit, drill string, a plurality of RF antennas, and at least one gradient coil. The tool further comprises a plurality of magnets that are polarized in a direction parallel to the longitudinal axis of the tool but opposite to each other. The configuration of magnets and antennas provides for at least two NMR regions of investigation.

Apparatus and method for obtaining a nuclear magnetic resonance measurement while drilling

The present invention is directed to a method for computing a distribution of spin&mdash;spin relaxation times. The spin-echo amplitudes are obtained by hardware integration of the receiver voltages over a time window. A linear operator is utilized to map a relaxation-time distribution to spin-echoes, produce a singular value decomposition (SVD) of the linear operator, determine vectors of the SVD, and compress the spin-echo data using the vectors. To eliminate a telemetry bottleneck, the T,spectrum is computed downhole and transmitted to the surface.

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Stafford, TX, United States of America

Bruno Luong