A diffusion magnetic resonance (MR) method for non-invasively visualizing geochemistry and microstructures of porous sedimentary rock samples. The method provides quantification of pore sizes, pore size distribution and measure on pore eccentricities even for heterogeneous samples with inter connections and three-dimensional organization and in the presence of free water or other liquids. No a priori knowledge on the sizes or distribution is required.
Our novel technology utilizes an angular bipolar double-pulsed-field gradient (bp-d-PFG) operated with variance in multiple parameters. A novel analysis reconstructs the pore size distribution (termed concentric Double PFG, CDPFG). This implementation method is unique, and our experimental results (see supporting publications) are the first that demonstrate such capability.
Figure: Reconstruction of pore size distribution obtained from a CDPFG experiment applied over micro-capillary phantom with capillaries of 3 radii (left) and 5 radii (right). Plots compare the experimentally set distribution (blue), with the reconstructed distributions (red).
Noninvasive determination of pore size and shape in different rocks and sediments is of importance in different geological application and in particular for the petroleum and logging industries. These parameters are indices that enable estimation of the amount of capillary-bound water – which in turn allows for determination of efficient oil and gas excavation/production potential.
Most diffusion MR methods use single pulsed-field-gradient (PFG) MR sequences; however such sequences are only beneficial for measurement of uniform, highly ordered media.
Conventional microscopy techniques (such as optics and X-ray) exhibit tremendous spatial resolution to image porous media; however, they are limited to laboratories and small samples. Also, optical imaging techniques are sensitive only to the surfaces of samples.
With the development of inside-out NMR systems such as well-logging and the NMR-Mouse, the present MR method is suitable for both field and laboratory exploration and analysis.
- Determining pore size, shape and organization by non-invasive, non-destructive MR.
- Volumetric data is gathered, rather than superficial information imaged by microscopy.
- Ability of obtaining structural information on samples having poly-disperse, randomly oriented pores (characterized by magnetic in-homogeneities), with large background gradients.
- Field analysis potential.
Two patent application families: PCT/IL2011/000506 (Cohen) and PCT/IL2012/050307 (Nevo)
- Non-invasive bipolar double-PFG NMR reveals signatures for pore size and shape in polydisperse, randomly oriented inhomogeneous porous media, J. Chem. Phys. 133, 044705 (2010).
- Probing microscopic architecture of opaque heterogeneous systems using double-PFG NMR, J. Am. Chem. Soc. 133, 6028-6035 (2011)
- Overcoming apparent-susceptibility-induced-anisotropy (aSIA) by Bipolar double-pulsed-field-gradient NMR, J. Magn. Reson. 212, 362-369 (2011)
- A proposed 2D framework for estimation of pore size distribution by double pulsed field gradient NMR, J. Chem. Phys. 137, 224201 (2012)
- Estimation of pore size distribution using concentric double pulsed-field 3 gradient NMR, In press J. Magn. Reson. (Available online)