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US 5,705,927 AGranted
Pulsed nuclear magnetism tool for formation evaluation while drilling including a shortened or truncated CPMG sequence
AssigneeSchlumberger Technology Corporation
InventorsAbdurrahman Sezginer, Douglas D. Griffin
Life of this patent
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Abstract
The instruments of a pulsed nuclear magnetic resonance (NMR) device are included in a drill collar for evaluating earth formations. The resulting tool makes NMR measurements while the formation is being drilled. Permanent magnets produce a static field in the earth formation. Shimming permanent magnets inside or outside the drill collar suppress the magnetic resonance of borehole fluids. The permanent magnets are manufactured from two magnetic materials, for example.
Claims9
A method for determinng a characterisitc of formations surrounding a borehole, comprising:
- drilling the borehole in the earth formation;
- using a tool to drill the borehole;
- directing fluid through the tool and into the borehole;
- using the tool to obtain NMR measurements while the borehole is being drilled;
- generating, from the tool, a sufficiently short sequence of magnetic pulses to minimize 2t.sub.cp J such that the NMR measurements are tolerant to vibrations of the tool while the borehole is being drilled, where t.sub.cp is the Carr-Purcell spacing and J is the number of echoes collected in a single Carr-Purcell-Meiboom-Gill (CPMG) sequence;
- and
- determining a characterisitc of the formation.
4 more elements
Dependencies are inferred from the claim text.