# US 6,720,765 B2 · High-resolution high-speed NMR well logging device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,720,765 B2 - Document ID: US6720765B2 - Status: Granted - Kind: B2 - Application number: 09/870,287 - Filed: 2001-05-30 - Published: 2002-12-05 - Granted: 2004-04-13 - Earliest claimed: 2001-05-30 - Assignees: Baker Hughes Incorporated - Inventors: Carl M. Edwards; Daniel T. Georgi - Web page: https://patentgrep.com/patent/US6720765B2 ## 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 - Y02A 90/30: Assessment of water resources - 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) - Y02A: TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE ## Abstract Wireline NMR well logging measurements suffer from disadvantages of poor vertical resolution, logging speeds less than 20 ft/min, and power consumption in excess of 200 W. In spite of these disadvantages, NMR well logging is used because it is capable of providing estimates for a number of petrophysical parameters that are difficult to obtain from other wireline data. These include estimates of the bulk volume irreducible (BVI) of fluids in the formation. The present invention targets BVI and clay bound water (CBW) measurements. Logging speeds of up to 60 ft/min are attainable with little or no loss of resolution. In one preferred embodiment, the tool has four sensors circumferentially distributed around the logging tool and in contact with the borehole wall. A horseshoe like magnet is used to generate the static magnetic field. The magnet poles are designed such that the magnetic field is uniform perpendicular tool motion, as well as provide a sufficiently large extent of the static field to provide polarization for bound water in rock formations. The RF portion of the sensor is comprised of at least one coil configured for transmission of an RF magnetic field into rock formations and at least two coils configured to separately receive the NMR signal from the formation. In another embodiment a coil is wound around the pole pieces or the iron yoke for the purpose of field shifting to enable acquisition of phase-alternated measurements. ## Claims ### Claim 1 A tool conveyed in a borehole for nuclear magnetic resonance (NMR) logging of an earth formation comprising: (a) a housing defining a longitudinal axis of the tool; (b) at least one sensor assembly coupled to the housing by an extension device, a body of said at least one sensor assembly adapted to make contact with a wall of a borehole in the earth formation, said sensor assembly including (A) a magnet for providing a static magnetic field in a sensitive region in said formation, (B) a transmitter coil for producing a pulsed radio frequency (RF) magnetic field in said sensitive region, and, (C) at least one receiver coil for receiving spin echo signals from nuclei in said sensitive region, said at least one receiver coil having an axis substantially parallel to an axis of said transmitter coil; wherein an axial extent of the transmitter coil is greater than an axial extent of the at least one receiver coil. ### Claim 2 (depends on 1) The logging tool of claim 1 wherein said at least one sensor assembly further comprises a plurality of sensor assemblies circumferentially distributed about said housing. ### Claim 3 (depends on 1) The logging tool of claim 1 wherein said extension device is operated by one of (i) a spring, (ii) hydraulic power, and, (iii) electrical power. ### Claim 4 (depends on 1) The logging tool of claim 1 wherein said magnet is a U-shaped magnet and further comprises; (i) a first magnet and a second magnet having a magnetization direction perpendicular to said longitudinal axis of the tool comprising arms of the U, said first and second magnets having opposite directions at magnetization, and (ii) a magnetically permeable yoke forming the base of the U. ### Claim 5 (depends on 4) The logging tool of claim 4 wherein a gap between ends of the first and second magnet away from the yoke is adjustable. ### Claim 6 (depends on 1) The logging tool of claim 1 wherein said RF magnetic field is produced by activating the transmitter coil with one of (i) a CPMG sequence, and, (ii) a modified CPMG sequence having a refocusing angle less than 180°. ### Claim 7 (depends on 1) The logging tool of claim 1 wherein said RE magnetic field has a field direction substantially orthogonal to said longitudinal axis and to a direction of the static magnetic field in said sensitive volume. ### Claim 8 (depends on 1) The logging tool of claim 1 wherein the at least one receiver coil further comprises at least two receiver coils offset along the longitudinal axis. ### Claim 9 (depends on 8) The logging tool of claim 8 further comprising a processor for using the spin echo signals from the at least two receiver coils for determining a parameter of interest of the earth formation. ### Claim 10 (depends on 8) The logging tool of claim 8 wherein said at least one sensor assembly is adapted to be rotated to a position wherein said at least two receiver coils are at substantially the same longitudinal position. ### Claim 11 (depends on 1) The logging tool of claim 1 further comprising a field shifting electromagnet including a coil for adjusting a position of the sensitive region. ### Claim 12 (depends on 1) The logging tool of claim 1 wherein the at least one receiver coil is displaced towards the borehole wall from the transmitter coil. ### Claim 13 (depends on 1) The logging tool of claim 1 further comprising a processor for using the spin echo signals from the at least one receiver coil for determining a parameter of interest of the earth formation. ### Claim 14 (depends on 13) The logging tool of claim 13 wherein the parameter of interest is at least one of(i) clay bound water, and, (ii) bulk volume irreducible. ### Claim 15 (depends on 1) The logging tool of claim 1 wherein said magnet has a higher magnetization at an end than at a middle portion of said magnet. ### Claim 16 A sensor assembly for nuclear magnetic resonance (NMR) measurements from a medium comprising: (a) a U-shaped magnet including a pair of magnets having opposed magnetization coupled by a permeable yoke for providing a static magnetic field in a sensitive region in the medium; (b) a transmitter coil for producing a pulsed radio frequency (RF) magnetic field in said sensitive region; and, (c) at least one receiver coil fin receiving spin echo signals from nuclei in said sensitive region, said at least one receiver coil having an axis substantially parallel to an axis of said transmitter coil. ### Claim 17 (depends on 16) The sensor assembly of claim 16 wherein said RF magnetic field is produced by activating the transmitter coil with one of (i) a CPMG sequence, and, (ii) a modified CPMG sequence having a refocusing angle less than 180°. ### Claim 18 (depends on 16) The sensor assembly of claim 16 wherein the at least one receiver coil further comprises at least two spaced apart receiver coils. ### Claim 19 (depends on 16) The sensor assembly of claim 16 further comprising a processor for using the spin echo signals from the at least two receiver coils for determining a parameter of interest of the earth formation. ### Claim 20 (depends on 16) The sensor assembly of claim 16 further comprising a field shifting electromagnet including a coil for adjusting a position of the sensitive region. ### Claim 21 (depends on 16) The sensor assembly of claim 16 wherein said transmitter coil is positioned between the at least one receiver coil and the permeable yoke. ### Claim 22 (depends on 16) The sensor assembly of claim 16 wherein a gap between ends of the first and second magnet away from the yoke is adjustable. ### Claim 23 (depends on 16) The sensor assembly of claim 16 further comprising a processor for using the spin echo signals from the at least one receiver coil for determining a parameter of interest of the earth formation. ### Claim 24 A method of determining a parameter of interest of an earth formation comprising: (a) conveying a logging tool having a longitudinal axis in a borehole in the earth formation; (b) using a U-shaped magnet on at least one sensor assembly for producing a static magnetic field in a sensitive region in said formation, said at least one sensor assembly coupled to a housing of the logging tool by an extension device; (b) using a transmitter coil on the at least one sensor assembly for producing a pulsed radio frequency (RF) magnetic field in said sensitive region; and, (c) using at least one receiver coil on the at least one sensor assembly for receiving spin echo signals from nuclei in said sensitive region, said at least one receiver coil having an axis substantially parallel to an axis of said transmitter coil. ### Claim 25 (depends on 24) The method of claim 24 wherein said at least one sensor assembly further comprises a plurality of sensor assemblies circumferentially distributed about said housing; the method further comprising obtaining information about an azimuthal variation of said parameter of interest. ### Claim 26 (depends on 24) The method of claim 24 wherein the plurality of sensor assemblies comprises three, and wherein the parameter of interest comprises bound volume irreducible, the method further comprising determining a dip and azimuthal direction of the formation. ### Claim 27 (depends on 25) The method of claim 25 wherein the plurality of sensor assemblies comprises three, and wherein the parameter of interest comprises clay bound water, the method further comprising determining a dip and azimuthal orientation of shale laminations. ### Claim 28 (depends on 25) The method of claim 25 wherein the plurality of sensor assemblies comprises three and wherein the parameter of interest comprises clay bound water and bulk volume irreducible, the method further comprising determining dip and cross-bedding of the formation. ### Claim 29 (depends on 24) The method of claim 24 further comprising operating the extension device by one of (i) a spring, (ii) hydraulic power, and, (iii) electrical power. ### Claim 30 (depends on 24) The method of claim 24 wherein said U-shaped magnet further comprises: (i) a first magnet and a second magnet having a magnetization direction perpendicular to said longitudinal axis of the tool comprising arms of the U, said first and second magnets having opposite directions of magnetization, and (ii) a magnetically permeable yoke forming the base of the U. ### Claim 31 (depends on 24) The method of claim 24 wherein producing said pulsed RF magnetic field further comprises modulating a RF signal by one of (i) a CPMG sequence, and, (ii) a modified CPMG sequence having a refocusing angle less than 180°. ### Claim 32 (depends on 24) The method of claim 24 wherein said RF magnetic field has a field direction substantially orthogonal to said longitudinal axis and to a direction of the static magnetic field in said sensitive volume. ### Claim 33 (depends on 24) The method of claim 24 wherein the at least one receiver coil further comprises at least two receiver coils offset along the longitudinal axis. ### Claim 34 (depends on 33) The method of claim 33 further comprising using a processor for determining from the spin echo signals from the at least two receiver coils the parameter of interest of the earth formation. ### Claim 35 (depends on 33) The method of claim 33 further comprising: (i) rotating said sensor assembly to position said at least two receiver coils at substantially the same longitudinal position; and (ii) obtaining said spin echo signals with an increased azimuthal resolution. ### Claim 36 (depends on 24) The method of claim 24 further comprising using a field shifting electromagnet including a coil for adjusting a position of the sensitive region in the formation. ### Claim 37 (depends on 36) The method of claim 36 further comprising repeating steps (a)-(c) for a different positions of the sensitive region using a phase alternated pulse sequence. ### Claim 38 (depends on 24) The method of claim 24 wherein the transmitter coil has a greater length along the longitudinal axis than the at least one receiver coil, the method further comprising moving the logging tool along the longitudinal axis while making continuing measurements. ### Claim 39 (depends on 24) The method of claim 24 further comprising adjusting a gap between ends of the first and second magnet away from the yoke and adjusting a position of the sensitive region. ### Claim 40 (depends on 24) The method of claim 24 further comprising using a processor for determining from the spin echo signals from the at least one receiver coil the parameter of interest of the earth formation. ### Claim 41 (depends on 24) The method of claim 24 wherein the parameter of interest comprises at least one of (i) clay bound water, and, (ii) bulk volume irreducible. ### Claim 42 (depends on 41) The method of claim 41 wherein producing said pulsed RF magnetic field further comprises modulating a RF signal with a modulating signal that is one of(A) a CPMG sequence, and, (B) a modified CPMG sequence having a refocusing angle less than 180°. ### Claim 43 (depends on 42) The method of claim 42 wherein said modulating signal includes short interecho spacings for determining a rapidly decaying component of a T2 distribution. ### Claim 44 A method of determining a parameter of interest of a medium comprising: (a) using a U-shaped magnet including a pair of magnets with opposed polarization coupled by a magnetically permeable yoke for producing a static magnetic field in a sensitive region in the medium; (b) using a transmitter coil for producing a pulsed radio frequency (RF) magnetic field in said sensitive region; and, (c) using at least one receiver coil having an axis substantially parallel to an axis of said transmitter coil for receiving spin echo signals from nuclei in said sensitive region. ### Claim 45 (depends on 44) The method of claim 44 wherein producing said pulsed RF magnetic field further comprises modulating a RF signal by one of(i) a CPMG sequence, and, (ii) a modified CPMG sequence having a refocusing angle less than 180°. ### Claim 46 (depends on 44) The method of claim 44 wherein said RF magnetic field has a field direction substantially orthogonal to said longitudinal axis and to a direction of the static magnetic field in said sensitive volume. ### Claim 47 (depends on 44) The method of claim 44 wherein the at least one receiver coil further comprises at least two receiver coils offset along a direction substantially perpendicular to a direction of the static magnetic field in the sensitive region. ### Claim 48 (depends on 44) The method of claim 44 comprising using a field shifting electromagnet including a coil for adjusting a position of the sensitive region in the formation. ### Claim 49 (depends on 48) The method of claim 48 further comprising repeating steps (a)-(c) for a different position of the sensitive region using a phase alternated pulse sequence. ### Claim 50 (depends on 44) The method of claim 44 further comprising adjusting a gap between ends of the first and second magnet away from the yoke and adjusting a position of the sensitive region. ### Claim 51 (depends on 44) The method of claim 44 further comprising using a processor for determining from the spin echo signals from the at least one receiver coil the parameter of interest of the earth formation. ### Claim 52 A logging tool conveyed in a borehole for nuclear magnetic resonance (NMR) logging of an earth formation comprising: (a) a housing defining a longitudinal axis of the tool; (b) at least one sensor assembly coupled to the housing by an extension device, a body of said at least one sensor assembly adapted to make contact with a wall of a borehole in the earth formation; (c) a U-shaped magnet on the at least one sensor assembly for providing a static magnetic field in a sensitive region in said formation; (d) a transmitter coil on the at least one sensor assembly for producing a pulsed radio frequency (RF) magnetic field in said sensitive region; (e) at least two spaced apart receiver coils for receiving spin echo signals from nuclei in said sensitive region, said at least two spaced apart receiver coils having axes substantially parallel to an axis of said transmitter coil; and (f) a processor for processing said received signals and a phase thereof for obtaining a high resolution estimate of a parameter of interest of the formation. ### Claim 53 A method of determining a parameter of interest of an earth formation comprising: (a) conveying a logging tool having a longitudinal axis in a borehole in the earth formation; (b) using a U-shaped magnet on at least one sensor assembly for producing a static magnetic field in a sensitive region in said formation, said at least one sensor assembly coupled to a housing of the logging tool by an extension device; (b) using a transmitter coil on the at least one sensor assembly for producing a pulsed radio frequency (RF) magnetic field in said sensitive region; and, (c) using at least two receiver coils on the at least one sensor assembly for receiving spin echo signals from nuclei in said sensitive region, said at least two receiver coils having axes substantially parallel to an axis of said transmitter coil; (d) using a processor for processing said received signals and a phase thereof for obtaining the parameter of interest.