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Related Experiment Videos

Fixed and pulsed gradient diffusion methods in low-field core analysis.

Gabriela Leu1, Edmund J Fordham, Martin D Hürlimann

  • 1Schlumberger-Doll Research, Ridgefield, CT 06877, USA.

Magnetic Resonance Imaging
|April 19, 2005
PubMed
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Effect of off-resonance on T<sub>1</sub> saturation recovery measurement in inhomogeneous fields.

Journal of magnetic resonance (San Diego, Calif. : 1997)·2017

Diffusion/relaxation time (D, T2) protocols are reviewed for sedimentary rocks. Pulsed field gradient (PFG) methods offer advantages over fixed field gradient (FFG) for laboratory petrophysics, especially in rocks with internal gradients.

Area of Science:

  • Geophysics
  • Petrophysics
  • Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

  • Diffusion-weighted relaxation protocols are crucial for characterizing fluid-saturated sedimentary rocks.
  • Low-field NMR (<= 2 MHz for 1H) is typical for oil-well logging tools.
  • Understanding diffusion (D) and relaxation time (T2) distributions is key to rock property analysis.

Purpose of the Study:

  • To review diffusion-weighted relaxation protocols for 2D (D, T2) distributions.
  • To evaluate these protocols for fluid-saturated sedimentary rocks under low magnetic fields.
  • To compare Fixed Field Gradient (FFG) and Pulsed Field Gradient (PFG) methods.

Main Methods:

  • Comparison of various FFG and PFG protocols using direct or stimulated echoes.

Related Experiment Videos

  • Application of protocols to liquids and two contrasting sedimentary rocks.
  • Investigation of low-field NMR conditions relevant to well-logging.

    • Main Results:

    • All protocols yielded comparable results for liquids and rocks with negligible internal gradients.
    • Strong internal gradients in rocks caused protocol-dependent artifacts in (D, T2) distributions.
    • PFG methods demonstrated advantages in signal-to-noise ratio, acquisition time, and reduced contamination.

    Conclusions:

    • PFG protocols offer significant advantages for laboratory petrophysics, particularly for rocks with strong internal gradients.
    • Both PFG and FFG methods can be implemented in a single apparatus, enabling versatile petrophysical studies.
    • Protocol selection is critical for accurate (D, T2) characterization, especially in heterogeneous rock samples.