Using diffusion and electrical measurements to assess tortuosity of porousmedia

This study puts under scrutiny the unique relationship between molecular di ffusion and electrical conductivity data for Berea, Okesa, Tallant, and Elg in sandstones ranging in permeability from 83 to 2502 md. The experimental setups used for generating the investigated data featured the use of a four -electrode circuit that canceled the effects of contact electrode polarizat ion and a diffusion flow system that allowed on-line calibration and establ ished a stable baseline. The effective molecular diffusion coefficients (De ) for these porous media were estimated by matching simulated concentration profiles with measured ones. Tortuosity values were calculated by using mo lecular diffusivity models and their analogous electrical conductivity mode ls. Tortuosity values calculated from diffusion measurements (using the Bra kel and Heertjes model; Int. J. Heat Transfer 1974, 17, 1093) matched reaso nably well with those values estimated using Pirson's electrical model (Geo logic Well Log Analysis; Gulf Publishing: Houston, TX, 1983). These results indicate the superiority of the latter model over a large number of format ion-factor-based models for estimating rock tortuosity. This study helped i n the selection of adequate tortuosity models for characterizing sandstone rocks and verified the similarity between electrical conductivity and molec ular diffusivity in sandstone rocks.