Figure 1

Concept of remote detection NMR. (a) A porous sample (shaded cylinder) is placed in the active volume of the encoding coil. Information is encoded as polarization of the sensor medium (gray spheres), flowing out of the sample into the detection coil. A more field-capable setup could be designed especially for encoding, for example, by using a single-sided magnet and a surface rf coil [4, 5, 6]. (b) A pulse sequence for remote detection NMR. The encoding rf pulse in the presence of the field gradient $G^{\mathrm{ss}}$ is applied to invert the magnetization only in a slice perpendicular to the gradient direction. A train of $n$ detection pulses is applied to measure the signal stroboscopically as the sensor medium gradually flows through the detection coil.Reuse & Permissions

Figure 2

Visualization of flow and dispersion through a rock sample. (a) TOF curves with slice-selective inversion of the spin magnetization along $z$. The position of the slice with respect to the center of the sample is indicated. The total gas pressure was 3 bar, and the flow rate was 0.55 slm. (b) Contour plot of the TOF curves with $z$ sampled in steps of 2.5 mm. The pressure was 2.5 bar, and the flow rate was 0.50 slm. (c) Time of the minimum (○) and width of the dip (×) in the signal as a function of the position of the inverted slice. The data are the same as in (b). The dashed lines in (b) and (c) represent the mean velocity, and the full line in (c) is a fit of the dispersion of the gas inside the rock as described in the text.Reuse & Permissions

Figure 3

Remote detection methods using phase encoding. (a) Gradient pulses in three directions, $G^{\mathrm{PE}}$, provide 3D modulation of the spin magnetization. The second $\pi /2$ pulse stores the magnetization along the applied field. (b) Sequence for slice-selective phase encoding. The bipolar gradient $G^{\mathrm{ss}}$ is used for slice selection in one dimension, while phase encoding gradient pulses $G^{\mathrm{PE}}$ are used to resolve the other two spatial dimensions. In both methods, detection is done by a train of pulses whose spacing defines the time resolution of the TOF experiment.Reuse & Permissions

Figure 4

Images of gas flow through the rock sample. The flow rate was 0.65 slm. The time between encoding and detection is indicated above each image. (a) A 3D representation of an isochronal surface at different times after the encoding step. The silhouettes represent the sample in its correct proportions, including the inlet and outlet. A 3D phase encoding sequence with hard encoding pulses was used. The total gas pressure was 3.7 bar. The resolution in all three dimensions was 0.46 cm. The experiment time was 36 min. (A movie of the complete data set is available for viewing [29].) (b) TOF $x\mathrm{\text{−}}z$ images with varying detection times after encoding. A slice of 0.75 cm thickness through the center of the rock was excited perpendicular to $y$, while $x$ and $z$ were resolved with 0.33 cm resolution using phase encoding. The pressure was 4.0 bar. The experiment time was 13 min.Reuse & Permissions