Method for processing NMR data without phase-alternating-pair (PAP) averaging
AssigneeBaker Hughes Incorporated
InventorSonghua Chen
Life of this patent
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Abstract
NMR data are acquired using a phase-alternation of the tipping pulse. Differences between consecutive samples acquired with same or different frequencies are determined and an average value of the differences is determined over a sample window and over a range of echoes. This average value, determined separately for the in-phase and quadrature component data is a measure of the systematic noise and may be applied to the in-phase and quadrature component data to give corrected data with a higher resolution than prior art methods of processing phase alternated pulse sequence data. The method may also be used to improve the resolution of multifrequency NMR data acquired with a gradient logging tool.
Claims15
A method for determining a parameter of interest of a volume of earth formation with a borehole tool conveyed in a borehole within the formation, the method comprising:
- (a) using a magnet assembly on the borehole tool for producing a static magnetic field having in said volume of the formation and aligning nuclear spins within said volume parallel to a direction of the static field;
- (b) producing a radio frequency (RF) magnetic field in said volume of the formation, said RF magnetic field having a first frequency and a direction substantially orthogonal to a direction of the static field, the RF field including a pulse sequence:
- T−τ−(R−τecho−τ)k−TW
- wherein T is a tipping pulse for tipping the nuclear spins at an angle substantially equal to ninety degrees to cause precession thereof, TW is a waiting time, τ is the Carr-Purcell time, R is a refocusing pulse and k=1, 2, . . . K, is the echo index, where k is the number of echoes collected in a single sequence of pulses;
- and (R−τ−echo−τ)k represents the time sequence from echo #1 to echo #K;
- (c) measuring with a receiver coil on the borehole tool in-phase and quadrature components of signals including a desired signal indicative of the response of the formation to the pulsed RF field, said measured in-phase and quadrature signals further including an additive systematic noise;
- (d) repeating steps (b) and (c) defining a plurality of samples at a plurality of depths in the borehole wherein a polarity of the tipping pulse is reversed between successive samples;
- and
- (e) processing said measured signals at the plurality of depths to determine a level of said additive systematic noise in said in-phase and quadrature component signals.
Dependencies are inferred from the claim text.