Ringing reduction in a nuclear magnetic resonance logging tool
A nuclear magnetic resonance (NMR) logging tool configured to be positioned in a borehole created in a subsurface formation. The NMR logging tool includes a magnet to induce a magnetic field in the subsurface formation, a transmission line, and a first shield positioned between the magnet and the transmission line. The NMR logging tool includes a transmitter and an antenna coupled to the transmitter by the transmission line. The antenna is to transmit a radio frequency (RF) magnetic field into the subsurface formation in response to the transmitter supplying power by the transmission line.
1. A nuclear magnetic resonance (NMR) logging tool comprising:
a magnet to induce a magnetic field in a subsurface formation;
a transmission line;
a first shield positioned between the magnet and the transmission line, wherein the first shield comprises a first metallic sheet having a thickness of at least nδ, wherein δ is a skin depth of the first metallic sheet and n is an integer greater than or equal to 1;
a transmitter; and
an antenna coupled to the transmitter by the transmission line, the antenna to transmit a radio frequency (RF) magnetic field into the subsurface formation in response to the transmitter supplying power by the transmission line.
2. The NMR logging tool of claim 1 , wherein n is an integer greater than or equal to 2.
3. The NMR logging tool of claim 1 , wherein the first metallic sheet is composed of at least one of copper and aluminum.
4. The NMR logging tool of claim 1 , further comprising
a housing that encases the magnet, the transmission line, the first shield, the transmitter, and the antenna; and
a second shield positioned between the housing and the transmission line.
5. The NMR logging tool of claim 4 , wherein the housing comprises:
a metallic section positioned over the transmission line and the magnet; and
a non-metallic section positioned over the antenna.
6. The NMR logging tool of claim 4 , wherein the second shield comprises one or more second metallic sheets.
7. The NMR logging tool of claim 6 , wherein the one or more second metallic sheets are composed of at least one of copper and aluminum.
8. The NMR logging tool of claim 1 , wherein the antenna is configured to detect an NMR response that has traversed the subsurface formation in response to the RF magnetic field.
9. A method comprising:
deploying a nuclear magnetic resonance (NMR) logging tool in a borehole created in a subsurface formation, the NMR logging tool comprising a magnet, a transmission line, a first shield positioned between the magnet and the transmission line and comprising a first metallic sheet having a thickness of at least nδ, wherein δ is a skin depth of the first metallic sheet and n is an integer greater than or equal to 1, a transmitter, and an antenna coupled to the transmitter by the transmission line;
inducing, by the magnet, a magnetic field in the subsurface formation;
powering, by the transmitter via the transmission line, the antenna;
inducing, by the antenna in response to the powering, a radio frequency (RF) magnetic field into the subsurface formation; and
detecting an NMR response that has traversed the subsurface formation that is in response to the RF magnetic field.
10. The method of claim 9 , further comprising determining properties of the subsurface formation based on the NMR response.
11. The method of claim 10 , further comprising performing a hydrocarbon recovery operation based on the properties of the subsurface formation.
12. The method of claim 9 , wherein n is an integer greater than or equal to 2.
13. The method of claim 9 , wherein the NMR logging tool comprises a housing that encases the magnet, the transmission line, the first shield, the transmitter, and the antenna and wherein the NMR logging tool comprises a second shield positioned between the housing and the transmission line.
14. The method of claim 13 , wherein the housing comprises:
a metallic section positioned over the transmission line and the magnet; and
a non-metallic section positioned over the antenna.
15. The method of claim 13 , wherein the second shield comprises one or more second metallic sheets.
16. A system comprising:
a downhole logging tool configured to be disposed within a wellbore; and
nuclear magnetic resonance (NMR) logging tool disposed within said downhole logging tool, said NMR logging tool comprising,
a magnet to induce a magnetic field in a subsurface formation;
a transmission line;
a first shield positioned between the magnet and the transmission line, wherein the first shield comprises a first metallic sheet having a thickness of at least nδ, wherein δ is a skin depth of the first metallic sheet and n is an integer greater than or equal to 1;
a transmitter; and
an antenna coupled to the transmitter by the transmission line, the antenna to transmit a radio frequency (RF) magnetic field into the subsurface formation in response to the transmitter supplying power by the transmission line.
17. The system of claim 16 , wherein n is an integer greater than or equal to 2.
18. The system of claim 16 , further comprising:
a housing that encases the magnet, the transmission line, the first shield, the transmitter, and the antenna; and
a second shield positioned between the housing and the transmission line.
19. The system of claim 18 , wherein the housing comprises:
a metallic section positioned over the transmission line and the magnet; and
a non-metallic section positioned over the antenna.