Apparatus and technique for NMR diffusion measurement

A method for conducting borehole NMR measurements comprising the steps of:

• 1. applying a static magnetic field to polarize nuclear spins in material at a given region of a borehole, thus creating bulk magnetization at the region;
• 2. applying an RF field to the region at a preselected frequency, duration and magnitude in order to cause at least part of the magnetization to lie in a plane horizontal to the plane of the borehole;
• 3. applying a fixed magnetic field gradient to the region, thereby allowing atoms and molecules of the material in the region of interest to diffuse in the gradient field;
• 4. applying a refocusing RF pulse to the region;
• 5. repeating step 3;
• 6. acquiring an NMR spin echo having an associated echo amplitude;
• and
• 7. deriving a diffusion coefficient D and/or a spin echo decay T2 from the echo amplitude.

A technique for conducting borehole NMR measurements comprising the steps of:

• 1. applying a static magnetic field to polarize nuclear spins in material at a given region of a borehole, thus creating bulk magnetization at the region;
• 2. applying an RF field to the region at a preselected frequency, duration and magnitude in order to cause at least part of the magnetization to lie in a plane horizontal to the plane of the borehole;
• 3. applying a time switched magnetic field gradient to the region, thereby allowing atoms and molecules of the material in the region to diffuse in the gradient field;
• 4. applying a refocusing RF pulse to the region;
• 5. repeating step 3;
• 6. acquiring an NMR spin echo having an associated echo amplitude;
• and
• 7. deriving a diffusion coefficient D and/or a spin echo decay T2 from the echo amplitude.

Apparatus for conducting borehole NMR measurements comprising:

• means for providing a magnetic field gradient of a predetermined magnitude at a desired location along a borehole, said magnetic field gradient being applied for a predetermined duration of time thereby allowing molecules in said location to diffuse;
• means for carrying out at least one NMR measurement in the presence of the magnetic field gradient by applying an RF field of a preselected frequency, said NMR measurement containing at least one echo;
• means for sensing a diffusion effect on the decay of at least the first of said at least one echo;
• and
• means for determining therefrom a diffusion coefficient.

Apparatus for conducting borehole NMR measurements comprising:

• means for applying a static magnetic field to polarize nuclear spins in material at a given region of a borehole, thus creating bulk magnetization at the region;
• means for applying an RF field to the region at a preselected frequency, duration and magnitude in order to cause at least part of the magnetization to lie in a plane horizontal to the plane of the borehole;
• means for applying a fixed magnetic field gradient to the region, thereby causing atoms and molecules of the material in the region to diffuse;
• means for applying a refocusing RF pulse to the region;
• means for reapplying the fixed magnetic field gradient to the region, thereby causing atoms and molecules of the material in the region to diffuse;
• means for acquiring an NMR spin echo and associated echo amplitude;
• and
• means for deriving a diffusion coefficient D or a spin echo decay T2 from the echo amplitude.

Apparatus for conducting borehole NMR measurements comprising:

• means for applying a static magnetic field to polarize nuclear spins in material at a given region of a borehole, thus creating bulk magnetization at the region;
• means for applying an RF field to the region at a preselected frequency, duration and magnitude in order to cause at least part of the magnetization to lie in a plane horizontal to the plane of the borehole;
• means for applying a time switched magnetic field gradient to the region, thereby causing the atoms and molecules of the material in the region to diffuse;
• means for applying a refocusing RF pulse to the region;
• means for reapplying the switched magnetic field gradient to the region, thereby causing atoms and molecules of the material in the region to diffuse;
• means for acquiring an NMR spin echo and associated echo amplitude;
• and
• means for deriving a diffusion coefficient D or a spin echo decay T2 from the echo amplitude.

A method for conducting NMR measurements of a material comprising the steps of:

• providing a magnetic field gradient at a desired location in the material from a magnet spaced externally with respect to the material;
• carrying out at least one NMR measurement in the presence of the magnetic field gradient, which measurement produces at least a first echo;
• sensing a diffusion effect on the decay of at least the first echo;
• and
• determining therefrom a diffusion coefficient.

A method for conducting NMR measurements comprising the steps of:

• 1. applying a static magnetic field to polarize nuclear spins in a material at a given region exterior to the source of the static magnetic field, thus creating bulk magnetization at the region;
• 2. applying an RF field to the region at a preselected frequency, duration and magnitude in order to cause at least part of the magnetization to lie in a plane perpendicular to the direction of the static magnetic field;
• 3. applying a fixed magnetic field gradient to the region, thereby allowing the atoms and molecules of the material in the region to diffuse in a gradient field;
• 4. applying a refocusing RF pulse to the region;
• 5. repeating step 3;
• 6. acquiring an NMR spin echo and associated echo amplitude;
• and
• 7. deriving a diffusion coefficient D and/or a spin echo decay T2 from the echo amplitude.

A method for conducting NMR measurements comprising the steps of:

• 1. applying a static magnetic field to polarize nuclear spins in a material at a given region exterior to the source of the static magnetic field, thus creating bulk magnetization at the region of interest;
• 2. applying an RF field to the region at a preselected frequency, duration and magnitude in order to cause at least part of the magnetization to lie in a plane perpendicular to the direction of the static magnetic field;
• 3. applying a time switched magnetic field gradient to the region, thereby allowing the atoms and molecules of the material in the region to diffuse in a gradient field;
• 4. applying a refocusing RF pulse to the region of interest;
• 5. repeating step 3;
• 6. acquiring an NMR spin echo and associated echo amplitude;
• and
• 7. deriving a diffusion coefficient D and/or a spin echo decay T2 from the echo amplitude.

Apparatus for conducting NMR measurements comprising:

• means for providing a magnetic field gradient at a desired location in a material located externally of the source of the magnetic field gradient;
• means for carrying out at least one NMR measurement in the presence of the magnetic field gradient, producing at least a first echo;
• means for sensing a diffusion effect on the decay of at least the first echo;
• and
• means for determining therefrom a diffusion coefficient.