NMR data acquisition with multiple interecho spacing
AssigneeBaker Hughes Incorporated
InventorsThomas Kruspe, Martin Blanz, Peter Rottengatter, Holger F. Thern
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Abstract
NMR data are acquired with variable spacing between refocusing pulses, giving data with a variable interecho time TE. Under certain conditions, diffusion effects can be neglected and data acquired with a multiple TE spacing may be used to obtain a T2 distribution with increased resolution and reduced power requirements. In gas reservoirs, the maximum TE may be determined from diffusion considerations using a dual wait time pulse sequence and this maximum TE is used to acquire data with dual TE. By proper selection of TE, echos can be obtained with significantly reduced ringing.
Claims5
A method for determining a parameter of interest of a volume of earth formation surrounding a borehole with a Nuclear Magnetic Resonance (NMR) logging tool conveyed in the borehole, the method comprising:
- (a) using a magnet assembly on the NMR 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 component in a direction orthogonal to a direction of the static field, the RF field including at least one pulse sequence comprising a tipping pulse and at least four refocusing pulses, each refocusing pulse producing at least one corresponding spin echo signal;
- and
- (c) measuring with the logging tool spin echo signals induced by the RE field in the formation;
- wherein at least three successive later ones of said at least four refocusing pulses of a single one of said at least one pulse sequence have a time intervals greater than time intervals between earlier successive refocusing pulses, and wherein at least one of said at least four refocusing pulses produces more than one echo signal.
Dependencies are inferred from the claim text.