Hydrodynamic dispersion and pore geometry in consolidated rock

Abstract

Experimental measurements of the dispersion of tracer particles in flow through natural porous media are compared with a percolation model. The experiments show that tracer dispersion is a sensitive function of the width of the pore-size distribution as measured by mercury capillary pressure. Measurements of capillary pressure (or electrical conductivity) are used to estimate the geometric correlation length of the dominant flow path in the rock. Percolation theory is used to derive a power-law relationship between the correlation length and the ratio of the dispersivity to the average grain size. The experimental value of the power-law exponent is in agreement with the theoretical prediction. Measurements on samples containing a residual saturation of wetting epoxy show no significant change in dispersion behavior. This result mediates against dispersion models requiring trapping in dead-end pores. Tracer concentration profiles exhibit anomalous long-time tails in two cases. In carbonate rocks, we associate long-time tails with macroscopic permeability heterogeneities. In sandstones, long-time tails occur in samples with a very narrow pore-size distribution. These samples may have permeability heterogeneities as a result of defects in the packing density. In the limit of low flow velocity, the long-time tail disappears, suggesting a convective mechanism associated with flow heterogeneities at a millimeter-or-larger scale.

Caracterização hidrodispersiva de dois solos da região irrigada do Vale do São Francisco

“…Os valores determinados para a dispersividade estão de acordo com os valores encontrados em trabalhos na literatura (Perfect et al, 2002;Vervoort et al, 1999;Gist et al, 1999). 2.…”

Enhanced gas recovery with CO2 sequestration: The effect of medium heterogeneity on the dispersion of supercritical CO2–CH4

“…Recently, there have been extensive studies on pre-asymptotic dispersion in various porous media (Bijeljic et al, 2011(Bijeljic et al, , 2013aBijeljic et al, 2013b;Blunt et al, 2013;Mitchell et al, 2008;Scheven et al, 2007;Scheven et al, 2005). Most of these focused on velocities in the transition region or above is Fickian-like and predominately dictated by restricted diffusion (Bijeljic et al, 2004;Gist et al, 1990;Levy and Berkowitz, 2003;Sahimi, 1995).…”

“…This type of breakthrough profile was also reported by Spence Jr. and Watkins (1980) who used xylene to miscibly displace iso-octane through San Andres carbonate cores from West Texas. Gist et al (1990) measured dispersion coefficients by injecting a pulse of concentrated NaCl (aq) through consolidated rocks. Long tail breakthrough profiles appeared in two of the five carbonates tested.…”

Enhanced dispersion by elastic turbulence in porous media

“…In contrast to periodic structures, random porous media typically also possess stagnant parts where the flow almost vanishes. Such stagnant parts are known to strongly influence the particle transport and dispersion [37][38][39]. Moreover, it has been observed that stagnant parts lead to the formation of vortices in viscoelastic fluids [40].…”