Abstract

Mass transfer in the diagenesis of sediments is accomplished by the movement of solutions, and by diffusion. In a recent paper, Garrels et al. (1949) showed that the rate of transport by diffusion is independent of the permeability, but dependent upon an “effective directional porosity.” Values of this parameter for several different rocks were determined by diffusion measurements. In view of the analogy which exists between diffusion and electrical conduction this result could have been predicted from electrical data, and the “effective directional porosity” is more easily determinable by electrical measurements.

In an open liquid-filled space the equations for diffusion and for electrical conduction, respectively, are:  

formula
where Dl and Kl are the diffusion constant and the electrical conductivity of the liquid.

In a rock composed of nonconductive minerals, diffusion and electrical conduction will occur only in the pore space, and along sinuous paths. Hence, in such a case, the effective diffusion constant and electrical conductivity will be given by  

formula
where f is the porosity and L a “lithologic factor” depending upon the sinuosity of the path. The geometrical factor f/L is the “effective directional porosity” of Garrels et al. It is the same for both electrical conduction and diffusion and can be determined much more easily by electrical than by diffusion measurements.

These deductions are confirmed by experiment and several tables of data for various rocks are presented.

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