Apparatus and methods for fast NMR well logging without instrument speed effects

Patent metadata

Field	Value
Publication number	US-9759832-B1
Application number	US-201615131185-A
Country	US
Kind code	B1
Filing date	Apr 18, 2016
Priority date	Apr 18, 2016
Publication date	Sep 12, 2017
Grant date	Sep 12, 2017

Abstract

An apparatus for NMR properties of subsurface formations includes a magnet, a transmitter antenna and at least one of a receiver section of the transmit antenna or a separate receiver antenna having a length along the longitudinal dimension of the apparatus which is shorter than a length of the transmitter antenna along the longitudinal dimension. The apparatus includes circuitry for applying radio frequency current pulses to the entire transmitter antenna and for receiving signals by the at least one of the receiver section of the transmitter antenna and the separate receiver antenna.

First claim

What is claimed is:

1. An apparatus for measuring nuclear magnetic resonance (NMR) properties of subsurface formations, comprising:
a magnet having a selected length for pre-polarizing nuclear spins in the formations;
a transmitter antenna;
at least one of a receiver section of the transmitter antenna and a separate receiver antenna having a length along the longitudinal dimension of the apparatus which is shorter than a length of the transmitter antenna along the longitudinal dimension; and
circuitry for applying radio frequency current pulses to the entire transmitter antenna and for receiving signals by the at least one of the receiver section of the transmitter antenna and the separate receiver antenna;
wherein the circuitry comprises a multiple frequency transmitter, and wherein the circuitry is configured to successively apply radio frequency current pulses through the entire transmitter antenna at each of a plurality of different frequencies; and
wherein the circuitry is configured to shape the current pulses such that magnetization of the formations is substantially undisturbed other than in a region having a static magnetic field amplitude corresponding to the frequency of the current pulses being transmitted.

2. The apparatus of claim 1 wherein the successively applied radio frequency current pulses at each of the plurality of frequencies is performed with substantially no delay between the end of the current pulses at one frequency and the beginning of the current pulses at the successive frequency.

3. The apparatus of claim 1 wherein the transmitter antenna length is an integer multiple of the at least one of the receiver section of the transmitter antenna and the separate receiver antenna.

4. The apparatus of claim 3 wherein the integer multiple is one less than a number of different frequencies generated by the circuitry for applying radio frequency pulses to the transmitter antenna.

5. The apparatus of claim 4 wherein the product of a number of measurement cycles, a speed of motion of the apparatus, and a measurement cycle time Tm are chosen such that their product is substantially equal to the transmitter antenna length.

6. The apparatus of claim 1 wherein the circuitry is configured to passively or actively disable a remainder of the transmitter antenna.

7. The apparatus of claim 1 wherein the magnet is configured to induce a static magnetic field having a substantially constant amplitude at a selected lateral distance from the magnet along a longitudinal direction at least equal in length to a length of the transmitter antenna.

8. The apparatus of claim 7 wherein the magnet is configured such that the substantially constant amplitude is related to a lateral distance from the magnet within a selected lateral distance range.

9. The apparatus of claim 1 wherein the apparatus is configured to be moved along a wellbore using at least one of armored electrical cable, a drilling assembly, tractor, coiled tubing and slickline.

10. The apparatus of claim 1 wherein the transmitter antenna and the separate receiver antenna comprise coaxially aligned coils.

11. A method for measuring nuclear magnetic resonance (NMR) properties of subsurface formations, comprising:
inducing a static magnetic field in the formation for pre-polarizing nuclear spins;
passing a plurality of radio frequency current pulses through a transmitter antenna; and
detecting NMR signals, the detecting performed by at least one of a receiver portion of the transmitter antenna and a separate receiver antenna, the at least one of a receiver section and the separate receiver antenna having a length which is shorter than a length of the transmitter antenna along a longitudinal dimension of the transmitter antenna;
wherein each of the plurality current pulses is shaped such that magnetization of the formations is substantially undisturbed other than in a region having a static magnetic field amplitude corresponding to the frequency of the plurality of current pulses.

12. The method of claim 11 wherein the plurality of radio frequency current pulses are applied successively at each of a plurality of different frequencies corresponding to a plurality of measurement cycles.

13. The method of claim 11 wherein the plurality of radio frequency current pulses comprises at least one pulse sequence having a first number of current pulses and at least one pulse sequence having a second number of current pulses smaller than the first number.

14. The method of claim 11 wherein the static magnetic field has substantially constant amplitude in a longitudinal direction at a selected lateral distance into the subsurface formations.

15. The method of claim 14 wherein the amplitude of the static magnetic field is related to the lateral distance from the magnet.

16. The method of claim 11 wherein a sensitivity distribution of the transmitter antenna is different from a longitudinal length of the transmitter antenna.

17. The method of claim 16 wherein the plurality of radio frequency current pulses are applied successively at each of a plurality different frequencies during each of a plurality of measurement cycles.

18. An apparatus for measuring nuclear magnetic resonance (NMR) properties of subsurface formations, comprising:
a magnet having a selected length for pre-polarizing nuclear spins in the formations;
a transmitter antenna;
at least one of a receiver section of the transmitter antenna and a separate receiver antenna having a length along the longitudinal dimension of the apparatus which is shorter than a length of the transmitter antenna along the longitudinal dimension; and
circuitry for applying radio frequency current pulses to the entire transmitter antenna and for receiving signals by the at least one of the receiver section of the transmitter antenna and the separate receiver antenna;
wherein the transmitter antenna length is an integer multiple of the at least one of the receiver section of the transmitter antenna and the separate receiver antenna, and wherein the integer multiple is one less than a number of different frequencies generated by the circuitry for applying radio frequency pulses to the transmitter antenna.

19. The apparatus of claim 18 wherein the product of a number of measurement cycles, a speed of motion of the apparatus, and a measurement cycle time Tm are chosen such that their product is substantially equal to the transmitter antenna length.

Assignees

• Schlumberger Technology Corp

Inventors

• Freedman Robert
• Bachman Henry
• Dementyev Anatoly
• Taherian Reza

Classifications

• G01R33/3808

  Magnet assemblies for single-sided MR wherein the magnet assembly is located on one side of a subject only; Magnet assemblies for inside-out MR, e.g. for MR in a borehole or in a blood vessel, or magnet assemblies for fringe-field MR · CPC title

• G01R33/282

  Means specially adapted for hyperpolarisation or for hyperpolarised contrast agents, e.g. for the generation of hyperpolarised gases using optical pumping cells, for storing hyperpolarised contrast agents or for the determination of the polarisation of a hyperpolarised contrast agent · CPC title

• G01N24/08

  by using nuclear magnetic resonance (G01N24/12 takes precedence) · CPC title

• G01R33/3664

  Switching for purposes other than coil coupling or decoupling, e.g. switching between a phased array mode and a quadrature mode, switching between surface coil modes of different geometrical shapes, switching from a whole body reception coil to a local reception coil or switching for automatic coil selection in moving table MR or for changing the field-of-view (G01R33/3671 takes precedence) · CPC title

• G01V3/34

  Transmitting data to recording or processing apparatus; Recording data · CPC title