# US 5,705,927 A · Pulsed nuclear magnetism tool for formation evaluation while drilling including a shortened or truncated CPMG sequence

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- Number: US 5,705,927 A
- Document ID: US5705927A
- Status: Granted
- Kind: A
- Application number: 08/623,031
- Filed: 1996-03-28
- Granted: 1998-01-06
- Earliest claimed: 1992-07-30
- Assignees: Schlumberger Technology Corporation
- Inventors: Abdurrahman Sezginer; Douglas D. Griffin
- Web page: https://patentgrep.com/patent/US5705927A

## CPC

- G01V 3/32: operating with electron or nuclear magnetic resonance
- G01N 24/081: {Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity}
- G01R 33/383: using permanent magnets
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## 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.

## Claims

### Claim 1

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.

### Claim 2 (depends on 1)

The method of claim 1 wherein 2t.sub.cp J is approximately ten milliseconds.

### Claim 3 (depends on 2)

The method of claim 2 wherein the formation characterisitc is the bound fluid volume.

### Claim 4 (depends on 2)

The method of claim 2 wherein the formation characterisitc is the porosity.

### Claim 5 (depends on 2)

The method of claim 2 wherein the formation characterisitc is the unbound fluid volume.

### Claim 6 (depends on 1)

The method of claim 1 wherein the truncated pulse sequence is less than ten milliseconds.

### Claim 7 (depends on 6)

The method of claim 6 wherein the formation characterisitc is the bound fluid volume.

### Claim 8 (depends on 6)

The method of claim 6 wherein the formation characterisitc is the porosity.

### Claim 9 (depends on 6)

The method of claim 6 wherein the formation characterisitc is the bound fluid volume.