Nuclear magnetic resonance tool with active RF spoiler antenna
AssigneeBaker Hughes Incorporated
InventorsArcady Reiderman, David Beard
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Abstract
A novel nuclear magnetic resonance (NMR) probe design for operating in a bore hole to obtaining the NMR characteristics of a region of interest adjacent the bore hole, characterized by a main RF antenna, a magnet, and a spoiler antenna. The spoiler antenna performs as an active shield for generating a resultant RF field that forcefully mismatches the static magnetic field inside the bore hole and substantially does not affects the RF field or antenna sensitivity in the region of interest.
Claims44
A side-looking nuclear magnetic resonance (NMR) sensing apparatus for operating in a bore hole to sense NMR signals emanating from a region of interest in a formation adjacent the bore hole, the tool comprising:
- (a) a magnet for inducing a static magnetic field in the region of interest;
- (b) a transmitting antenna assembly for inducing a radio frequency (RF) magnetic field in a first region including the region of interest;
- (c) a receiving antenna assembly for receiving signals from a second region including the region of interest;
- and
- (d) a spoiler antenna assembly for spoiling the RF magnetic field so that the resultant RF field is forcefully mismatched to the static magnetic field in a portion of said second region outside the region of interest in order to reduce contributions to the sensed NMR signal therefrom, said portion including a portion of the bore hole.
A method of using a side-looking nuclear magnetic resonance (NMR) sensing apparatus in a bore hole to sense NMR signals emanating from a region of interest in a formation adjacent the bore hole, the method comprising:
- (a) using a magnet on the sensing apparatus for inducing a static magnetic field in the region of interest;
- (b) using a transmitting antenna assembly on the sensing apparatus for inducing a radio frequency (RF) magnetic field in a first region including the region of interest;
- (c) using a receive antenna assembly for receiving signals from a second region including the region of interest;
- and
- (d) using a spoiler antenna assembly on the sensing apparatus for altering the RF magnetic field so that the resultant RF field is forcefully mismatched to the static magnetic field in a portion of said second region outside the region of interest to reduce contributions to the sensed NMR signal therefrom, said portion including a portion of the bore hole.
Dependencies are inferred from the claim text.