Abstract: A downhole controller is used to tune the resonance frequency of an antenna after each NMR measurement sequence. At the end of the sequence, the downhole controller causes a pulse sequencer to generate a calibration pulse. The downhole controller then observes a voltage decay across the antenna after the calibration pulse. The downhole controller performs a Fast Fourier Transform (FFT) of the voltage decay to derive the resonant frequency of the antenna. The downhole controller determines a difference between the determined resonance frequency and the Larmor frequency and makes corresponding corrections by activating switches of the resonance tuning circuit. After each NMR measurement sequence, the downhole controller repeats the calibration to keep the antenna tuned to a frequency near the Larmor frequency.

Abstract: An NMR tool includes RF antennae and a cylindrical permanent magnet to establish a static magnetic B0 field for performing the NMR measurement sequence. The magnetic field of the magnet is polarized across the diameter of the magnet. A ferrite material is located adjacent to the permanent magnet. The antennae are located near opposite ends of the ferrite material and are formed from corresponding coils that are wound around the ferrite material such that the magnetic moments of the antennae are parallel to the longitudinal axis of the magnet.

Abstract: An NMR logging tool includes at least one antenna and a pulse sequencer. The pulse sequencer is coupled to said at least one antenna and is adapted to receive state descriptors that are indicative of states of an NMR measurement sequence. The pulse sequencer uses the antenna(e) to perform the NMR measurement sequence downhole in a subterranean formation in response to the state descriptors.

Abstract: A downhole controller is used to tune the resonance frequency of an antenna after each NMR measurement sequence. At the end of the sequence, the downhole controller causes a pulse sequencer to generate a calibration pulse. The downhole controller then observes a voltage decay across the antenna after the calibration pulse. The downhole controller performs a Fast Fourier Transform (FFT) of the voltage decay to derive the resonant frequency of the antenna. The downhole controller determines a difference between the determined resonance frequency and the Larmor frequency and makes corresponding corrections by activating switches of the resonance tuning circuit. After each NMR measurement sequence, the downhole controller repeats the calibration to keep the antenna tuned to a frequency near the Larmor frequency.

Abstract: An NMR tool includes RF antennae and a cylindrical permanent magnet to establish a static magnetic B0 field for performing the NMR measurement sequence. The magnetic field of the magnet is polarized across the diameter of the magnet. A ferrite material is located adjacent to the permanent magnet. The antennae are located near opposite ends of the ferrite material and are formed from corresponding coils that are wound around the ferrite material such that the magnetic moments of the antennae are parallel to the longitudinal axis of the magnet.