Method for correcting downhole NMR data contaminated by borehole signals
AssigneeBaker Hughes Incorporated
InventorsDan T. Georgi, Songhua Chen, Holger Thern
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Abstract
NMR measurements made in a borehole are susceptible to contamination by signals from the borehole fluid. Correction is made for this contamination by using a standoff measuring device to determine the fractional volume of the region of investigation of the NMR tool that lies within the borehole. Using known or determined characteristics of the borehole fluid, a correction is made either to the NMR signals prior to processing or to the processed results of the uncorrected signals.
Claims26
A method of determining a parameter of interest of earth formations using a nuclear magnetic resonance (NMR) logging tool having a volume of investigation conveyed in a borehole in the earth formations, the method comprising:
- (a) obtaining NMR signals indicative of the parameter of interest at at least one depth in the borehole, said obtained NMR signals including effects of a fluid in the borehole;
- (b) processing said obtained NMR signals to obtain an uncorrected value of the parameter of interest;
- (c) determining a fraction of the volume of investigation within the borehole and including said fluid, and determining a correction to the parameter of interest therefrom;
- and
- (d) determining the parameter of interest by applying said correction to said uncorrected value of the parameter of interest.
A method of determining a parameter of interest of earth formations using a nuclear magnetic resonance (NMR) logging tool having a volume of investigation conveyed in a borehole in the earth formations, the method comprising:
- (a) obtaining NMR signals indicative of the parameter of interest at at least one depth, said obtained NMR signals including effects of a fluid in the borehole;
- (b) determining a fractional volume of the volume of investigation within the borehole and including said fluid, and determining a correction to the obtained NMR signals therefrom;
- (c) applying said correction to the obtained NMR signals to obtain corrected NMR signals;
- and
- (d) processing said corrected NMR signals to obtain a corrected value of the parameter of interest.
Dependencies are inferred from the claim text.