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.
Claims31
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 said static magnetic field having a substantially time-invariant gradient;
- (b) producing a radio frequency (RF) magnetic field in said volume of the formation with an antenna on the NMR logging tool, said RF magnetic field having a component in a direction orthogonal to a direction of the static field, the RE 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 NMR logging tool spin echo signals induced by the RE field in the formation;
- wherein earlier successive ones of said at least four refocusing pulses of a single one of said at least one pulse sequence have a first time interval therebetween and at least three later successive ones of said at least four refocusing pulses of said at least one pulse sequence have a second time interval therebetween, said second time interval greater than the first time interval.
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 logging tool to produce a static magnetic field in said volume of the formation said static magnetic field having a substantially time-invariant gradient;
- (b) producing a radio frequency (RE) magnetic field in said volume of the formation with an antenna on the NMR, logging tool, said RE magnetic field having a component in a direction orthogonal to a direction of the static field, the RE 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 RF 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 time intervals greater than time intervals between earlier successive refocusing pulses.
A Nuclear Magnetic Resonance (NMR) logging tool for use within a borehole for determining a parameter of interest of a volume of earth formation surrounding the borehole, the logging tool comprising:
- (a) a magnet assembly for producing a static magnetic field in said volume of the formation said static magnetic field having a substantially time-invariant gradient;
- (b) an antenna for producing a pulsed radio frequency (RF) magnetic field in said volume of the formation and producing spin-echos therein, said RF magnetic field having a component in a direction orthogonal to a direction of the static field;
- (c) an antenna for producing signals indicative of said spin-echos;
- and
- (d) a processor for controlling the antenna with a pulse sequence including a single tipping pulse and at least four refocusing pulses, said at least four refocusing pulses having a first time interval between successive earlier ones of the refocusing pulses of said pulse sequence and a second time interval between at least three successive later ones of the refocusing pulses of said pulse sequence, said second time interval greater than the first time interval.
Dependencies are inferred from the claim text.