Permeability estimation from induced polarization: an evaluation of geophysical length scales using an effective hydraulic radius concept

Geophysical length scales defined from induced-polarization measurements can be used in models of permeability (k) prediction. We explore the relative merit of different induced-polarization parameters as proxies of an effective hydraulic radius (reff) that can be used to predict permeability from a modified Hagen–Poiseuille equation. Whereas geometrical measures of the hydraulic radius are good proxies of reff, the induced-polarization measures are not well correlated with reff. However, a new proxy of reff that considers both imaginary conductivity and formation factor shows an improved correlation with reff. The resulting model enables a better quality of permeability prediction compared with the other geophysical length scales, but does not reach the predictive quality of the models based on geometrical length scales. The specific polarizability defined when incorporating the effect of the formation factor on imaginary conductivity appears to be independent of pore geometry, indicating that it is the correct parameter representing the role of the surface electrochemistry on the induced-polarization effect. However, the joint dependence of induced-polarization measurements on both the pore radius and the tortuosity and porosity of the interconnected pore network is a limitation to the widely explored use of induced-polarization measurements to isolate surface properties from volumetric properties of the interconnected pore network

Determination of the distribution of air and water in porous media by electrical impedance tomography and magneto-electrical imaging

Monitoring the distribution of water content is essential for understanding hydrological processes in the lithosphere and the pedosphere. The movement of water in unsaturated rock formations and in the vadose zone is influenced by different processes (mainly infiltration, evaporation, percolation and capillary flow) which may be rate determining depending on the actual conditions. The interdependence of these processes also strongly influences the transport and distribution of solutes in the pore space. In order to gain a better understanding of the movement and distribution of water in unsaturated media, systematic investigations with non-invasive or minimal invasive methods appear to be most suitable. Studies on the distribution of electrical conductivity can improve risk analysis concerning waste disposals in general and nuclear waste repositories in particular. Induced polarization and magnetic flux density determined with two highly sensitive accessories yield additional information and may allow for better discrimination of coupled flow processes. Electrical impedance tomography (Err) with 20 current injection and 48 voltage electrodes was used here to monitor the evaporation of tap water from a container filled with sand under laboratory conditions at 20 degrees C. The results are compared with data obtained by determining spectral induced polarization (SIP) of sand during desaturation in a multi-step outflow equipment. Infiltration processes and evaporation from sand saturated with 0.01 M CaCl2 were determined by magneto-electrical resistivity imaging technique (MERIT). The results were obtained from a long-term experiment under controlled conditions. (C) 2010 Elsevier B.V. All rights reserved

Bismuth porphyrin complexes: syntheses and structural studies

International audienceThe synthesis of several new bismuth porphyrin complexes Bi(por)(X) containing the tpp or tpClpp (tpClpp = 5,10,15,20-tetra-chlorophenylporphyrin) porphyrin ligand and anions X = NO3, Cl, Br, I are described. Molecular structures reported for Bi(tpClpp)(X) for X = Cl, Br show that the complexes crystallise as centrosymmetric dimers doubly bridged through Cl or Br. Bi(tpClpp)(NO3) crystallises as a less symmetric dimer in which one NO3 ligand bridges the two bismuth centres and the second NO3 ligand interacts with only one bismuth atom. In all three structures the bismuth atoms are significantly displaced from the porphyrin N4 planes and the Bi–halide or Bi–O distances are very long