Estimating molecular size distributions in formation fluid samples using a downhole NMR fluid analyzer

Patent metadata

Field	Value
Publication number	US-9645277-B2
Application number	US-201313765414-A
Country	US
Kind code	B2
Filing date	Feb 12, 2013
Priority date	Feb 12, 2013
Publication date	May 9, 2017
Grant date	May 9, 2017

Abstract

A method for estimating a property of subsurface material includes extracting a sample of the material using a downhole formation tester and performing a plurality of nuclear magnetic resonance (NMR) measurements on a sensitive volume in the sample where each measurement in the plurality is performed in a static homogeneous magnetic field with a pulsed magnetic field gradient that is different in magnitude from other NMR measurements to provide a waveform signal. The method further includes transforming each received waveform signal from a time domain into a frequency domain and comparing the frequency domain signal to a reference to provide proton chemical-shift information related to a chemical property of one or more molecules in the sample and transforming the frequency domain signals into a complex number domain that quantifies waveform signal amplitude changes to provide one or more diffusion rates with each diffusion rate being associated with a corresponding frequency.

First claim

What is claimed is:

1. A method for estimating a property of subsurface material, the method comprising:
conveying a carrier through a borehole penetrating the subsurface material;
extracting a sample of the subsurface material using a formation tester disposed at the carrier;
performing a plurality of nuclear magnetic resonance (NMR) measurements on a sensitive volume in the sample using an NMR instrument, each measurement in the plurality of NMR measurements providing an electromagnetic waveform signal received with an antenna, each NMR measurement in the plurality of NMR measurements being performed (a) in a static homogeneous magnetic field, (b) with a sequence of pulses of radio-frequency (RF) electromagnetic energy transmitted from a transmitter antenna, and (c) with a series of pulsed magnetic field gradients being applied to the sample, the series of pulsed magnetic field gradients being superimposed over the static homogeneous magnetic field and the series of pulsed magnetic field gradients having a magnitude that is different from the magnitude of the series of pulsed magnetic field gradients in other NMR measurements;
transforming each received waveform signal from a time domain into a frequency domain to provide a frequency domain signal that is a function of frequency and comparing the frequency domain signal to a reference to provide proton chemical-shift information related to a chemical property of one or more molecules in the sample;
transforming the frequency domain signals having the same frequency as a function of the magnitude of the pulsed field gradient into a complex number domain that quantifies waveform signal amplitude changes to provide one or more diffusion rates with each diffusion rate being associated with a corresponding frequency; and
estimating the property using the proton chemical-shift information and the one or more diffusion rates.

2. The method according to claim 1 , further comprising relating the proton chemical-shift information to one or more chemical properties of one or more molecules.

3. The method according to claim 2 , further comprising relating the diffusion rates to a size of the one or more molecules.

4. The method according to claim 1 , wherein transforming each received waveform signal from a time domain into a frequency domain comprises using a Fourier transform.

5. The method according to claim 1 , wherein transforming the frequency domain signals comprises using a Laplace transform.

6. The method according to claim 1 , wherein the homogeneous magnetic field varies by less than 5 parts per million over the sensitive volume.

7. The method according to claim 1 , wherein a diameter of the sensitive volume is 500 microns or less.

8. The method according to claim 1 , wherein the property is a quantification of a distribution of one or more molecules in the sample.

9. The method according to claim 1 , further comprising identifying the subsurface material as at least one selection from a group consisting of saturates, aromatics, resins, and asphaltenes.

10. An apparatus for estimating a property of a subsurface material, the apparatus comprising:
a carrier configured to be conveyed through a borehole penetrating the subsurface material;
a formation tester disposed at the carrier and configured to extract a sample of the subsurface material;
a nuclear magnetic resonance (NMR) instrument disposed at the carrier and configured to perform a plurality of nuclear magnetic resonance (NMR) measurements on a sensitive volume in the sample, each measurement in the plurality of NMR measurements providing an electromagnetic waveform signal, each NMR measurement in the plurality of NMR measurements being performed (a) in a static homogeneous magnetic field, (b) with a sequence of pulses of radio-frequency (RF) electromagnetic energy transmitted from a transmitter antenna, and (c) with a series of pulsed magnetic field gradients being applied to the sample, the series of pulsed magnetic field gradients being superimposed over the static homogeneous magnetic field and the series of pulsed magnetic field gradients having a magnitude that is different from the magnitude of the series of pulsed magnetic field gradients in other NMR measurements, the NMR instrument comprising:
a magnetic field source configured to apply the homogeneous magnetic field to the sensitive volume;
a transmitter antenna configured to transmit a radio-frequency (RF) signal into the sensitive volume;
a pulsed magnetic field gradient source configured to apply the series of pulsed magnetic field gradients with various magnitudes to the sensitive volume;
a receiver antenna configured to receive the electromagnetic waveform signals from the sensitive volume due the RF signal and the pulsed magnetic field gradient; and

a processor configured to:
receive each of the electromagnetic waveform signals;
transform each received waveform signal from a time domain into a frequency domain to provide a plurality of frequency domain signals and compare the frequency domain signals to a reference to provide proton chemical-shift information related to a chemical structure of one or more molecules in the sample;
transform the frequency domain signals at the same frequency as a function of the magnitude of the pulsed field gradient into a complex number domain that quantifies waveform signal amplitude changes to provide one or more diffusion rates with each diffusion rate being associated with a corresponding frequency; and
estimate the property using the proton chemical-shift information and the one or more diffusion rates.

11. The apparatus according to claim 10 , further comprising a sample tube configured to contain the sample for the NMR measurements.

12. The apparatus according to claim 11 , wherein the magnetic field source comprises a Halbach array of magnets surrounding the sample tube, the array being configured to apply the homogeneous magnetic field to the sensitive volume.

13. The apparatus according to claim 11 , wherein the receiver antenna is a coil disposed inside of the sample tube and surrounds the sensitive volume.

14. The apparatus according to claim 13 , wherein the sample tube comprises an electrical penetration coupled to the coil.

15. The apparatus according to claim 13 , wherein the coil is a micro-coil fabricated as a micro-electrical-mechanical-system (MEMS) and having a diameter of 500 microns or less.

16. The apparatus according to claim 11 , wherein the sample container is a capillary tube.

17. The apparatus according to claim 15 , wherein the magnetic field source is a coil surrounding the capillary tube.

18. The apparatus according to claim 10 , wherein the pulsed magnetic field gradient source comprises a coil magnetically coupled to the sensitive volume.

Assignees

• Edwards Carl M
• Chen Jinhong
• Baker Hughes Inc

Inventors

• Edwards Carl M
• Chen Jinhong

Classifications

• G01V3/32 Primary

  operating with electron or nuclear magnetic resonance · CPC title

• G01N24/081 Primary

  Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity · CPC title

• G01R33/20

  involving magnetic resonance (medical aspects A61B5/055; magnetic resonance gyrometers G01C19/60) · CPC title

• E21B49/08 Primary

  Obtaining fluid samples or testing fluids, in boreholes or wells · CPC title