Methods and apparatus for measuring flow velocity in a wellbore using NMR and applications using same

A method of determining of measuring permeability of an earth formation, utilizing at least one nuclear magnetic resonance (NMR) tool that is placed in a wellbore in the formation and which produces a static magnetic field and measures induced magnetic signals, the method comprising:

• inducing the fluid to flow;
• applying the static magnetic field from the NMR tool to a volume of the formation, the static magnetic field polarizing a substantial portion of the formation that is subject to the static magnetic field;
• applying an oscillating magnetic field to a specific part of the polarized portion to induce the production of measurable signals, the oscillating magnetic field being applied in accordance with field maps B0 and B1 so that a resonance region having a specific shape corresponding to a desired sensitivity is formed in the formation;
• measuring the induced signals;
• taking a local pressure gradient measurement;
• deriving a horizontal component of flow velocity from the measurable induced signals;
• deriving a vertical component of flow velocity from the measurable induced signals;
• and
• deriving a measurement of permeability from the horizontal component, the vertical component and the local pressure gradient measurement.

A method of measuring permeability of an earth formation, the measurement utilizing a plurality of nuclear magnetic resonance (NMR) tools that are included within a drill string, the method comprising:

• inducing fluid to flow;
• applying a first static magnetic field from a first NMR tool to a first volume of the formation, the first static magnetic field polarizing a first substantial portion of the formation that is subject to the first static magnetic field;
• applying a first oscillating magnetic field to a specific part of the first polarized portion to induce the production of measurable signals, the first oscillating magnetic field being applied in accordance with specific field maps B0 and B1 to produce a first resonance region having a first specific shape corresponding to a first desired sensitivity formed in the formation the first resonance region having a sensitivity to radial flow;
• applying a second static magnetic field from a second NMR tool to a second volume of the formation, the second static magnetic field polarizing a second substantial portion of the formation that is subject to the second static magnetic field;
• applying a second oscillating magnetic field to a specific part of the second polarized portion to induce the production of measurable signals, the second oscillating magnetic field being applied in accordance with specific field maps B0 and B1 to produce a second resonance region having a second specific shape corresponding to a second desired sensitivity formed in the formation, the second resonance region having a sensitivity to vertical flow;
• measuring the induced signals;
• taking a local pressure gradient measurement;
• deriving a horizontal component of flow velocity from the measurable signals induced by the first NMR tool;
• deriving a vertical component of flow velocity from the measurable signals induced by the second NMR tool;
• and
• deriving a measurement of permeability from the horizontal component, the vertical component and the local pressure gradient measurement.