Schlumberger Technology Corporation

Van D M Koroleva

Soumyajit Mandal

Yi-Qiao Song

Martin D Hurlimann

Krishnamurthy Ganesan

Nicholas J Heaton

Martin D Hürlimann

Troy W Borneman

Payam Tabrizi

Gabriela Leu

A method for measuring one or more properties of a formation includes applying a magnetic field to a subterranean formation using a downhole tool. A radiofrequency signal is transmitted into the subterranean formation that is exposed to the magnetic field. The radiofrequency signal induces a transverse magnetization in the subterranean formation, and the transverse magnetization induces an initial voltage signal in the downhole tool. The initial voltage signal is amplified using a first amplifier in the downhole tool such that the first amplifier outputs a first amplified voltage signal. The first amplified voltage signal is introduced to an input of the first amplifier, such that the first amplifier amplifies the first amplified voltage signal and outputs a second amplified voltage signal.

Active damping for NMR logging tools

A method for applying a nuclear magnetic resonance (NMR) sequence is described herein. The method includes applying a series of refocusing pulses to a substance within an inhomogeneous static magnetic field. Each refocusing pulse in the series of refocusing pulses includes a central axis, a total pulse duration greater than t, and at least five segments (e.g., 5, 7, 11, 20, and 21). The phase of each segment is substantially anti-symmetric about the central axis of the refocusing pulse. In a more particular embodiment, the phase of each segment is also symmetric about the central axis of the refocusing pulse and the five segments include a substantially constant amplitude.

Nuclear magnetic resonance refocusing pulses for inhomogeneous magnetic fields

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Newton, MA, United States of America

Van D M Koroleva