Positron emission tomography for modelling of geochemical transport processes in clay

Abstract

The transport of water and salt solutions in unsaturated clay and clay rock was measured using the positron emission tomography (PET). The experimental device is described. KF marked with 18 F was used as conservative hydrodynamic tracer to image the flow profiles at different times. Homogeneous and heterogeneous flow regimes were identified. Hydrodynamic model parameters could be determined for the homogeneous regime. The results demonstrate the advantage of PET measurements for investigations of transport processes in geological matrices. They yield quantitative values of the spatial distribution in regard to the flow pattern inside the samples which are important for the validation and parameter estimation of geochemical transport models.

Geoscientific process monitoring with positron emission tomography (GeoPET)

“…Our work group systematically developed and applied PET scanners for geoscientific research in the course of over 1 decade (Richter and Gründig, 2000;Richter et al, 2005;Wolf et al, 2010;Gründig et al, 2002Gründig et al, , 2007Kulenkampff et al, 2008Kulenkampff et al, , 2010Kulenkampff et al, , 2013Kulenkampff et al, , 2015Barth et al, 2014a, b). The first published experiments were conducted with a selfconstructed PET scanner for soil columns and rock cores, designed for slow transport studies (Richter and Gründig, 2000).…”

“…Positron-emitting isotopes of virtually all natural elements exist. However, only a small fraction of theses nuclides can be produced with acceptable expenditure, and only a few nuclides are practically useful because decay time, positron energy, and other types of decay radiation have to be considered (Hawkesworth and Parker, 1995;Richter et al, 2005). We applied a number of GeoPET isotopes, which are listed in Table 1. PET makes use of the coincidence detection of the photon pair produced by the annihilation of the positron which occurs when a slowed down positron interacts with an electron.…”

Advanced spectroscopic, microscopic, and tomographic characterization techniques to study biogeochemical interfaces in soil

“…This approach allows the direct, noninvasive, 4D (3D+time) visualization of complex transport processes in natural geologic media. By applying PET-active radiotracers such as 18 F, it is possible to study the local flow profiles of the fluid even in low-permeability soil matrices (Richter et al 2005) and visualize them in the form of animations. The major benefit over other solute visualization techniques such as nuclear magnetic resonance tomography is that the required tracer activity for PET at the same spatial resolution is in the order of 10 -12 mol/l.…”

Imaging and modeling of flow in porous media using clinical nuclear emission tomography systems and computational fluid dynamics

“…Khalili et al (Khalili et al, 1998) used PET to visualize flow in porous sediments. More recently, a large body of PET research of transport of water and salt solutions in geomaterials was presented by a group in Leipzig, Germany (Richter et al, 2005; Gründig et al, 2007; Kulenkampff et al, 2008). Since flow velocities studied in hydrogeological experiments are low, 10 −4 cm/sec or less, the flow residence time in a typical column is of the order of hours or days.…”