RF sensor of a novel NMR apparatus (for petrophysical evaluation)

Author

Sezginer, A. ; Griffin, D.D. ; Kleinberg, R.L. ; Fukuhara, M. ; Dudley, D.G.

Author_Institution

Schlumberger-Doll Res., Ridgefield, CT, USA

fYear

1992

fDate

18-25 June 1992

Firstpage

900

Abstract

A pulsed-NMR (nuclear magnetic resonance) apparatus has been developed for petrophysical evaluation of earth formations. The instrument is deployed in boreholes drilled in the ground that are typically 20 cm in diameter and 0.5-5 km deep. The NMR measurement yields the volume fraction of the pores in the rock and the distribution of the pore sizes. A vital component of borehole NMR instruments is a near-field antenna that is used to transmit high-power RF pulses, to manipulate the nuclear spin state of the hydrogen nuclei. Similar to a radar, when the transmitter is off, the antenna receives a feeble RF pulse (a spin-echo) due to precessing nuclear magnetic moments. The design of the antenna requires extreme care, because the NMR signal induced in the antenna is comparable to the thermal noise generated in the antenna. The design goal is to maximize the signal to noise ratio, which is an increasing function of figure of merit.<>

Keywords

antennas; electric sensing devices; geophysical equipment; nuclear magnetic resonance spectroscopy; proton magnetic resonance; spin echo (NMR); 0.5 to 5 km; 20 cm; H nuclei; NMR measurement; NMR signal; boreholes; earth formations; figure of merit; high-power RF pulses; near-field antenna; nuclear magnetic moments; nuclear spin state; petrophysical evaluation; pore sizes; pulsed NMR apparatus; rock; signal to noise ratio; spin-echo; thermal noise; volume fraction; Antenna measurements; Earth; Instruments; Magnetic sensors; Nuclear magnetic resonance; Radar antennas; Radio frequency; Signal design; Transmitting antennas; Volume measurement;

fLanguage

English

Publisher

ieee

Conference_Titel

Antennas and Propagation Society International Symposium, 1992. AP-S. 1992 Digest. Held in Conjuction with: URSI Radio Science Meeting and Nuclear EMP Meeting., IEEE

Conference_Location

Chicago, IL, USA

Print_ISBN

0-7803-0730-5

Type

conf

DOI

10.1109/APS.1992.221806

Filename

221806