The equivalent channel model for permeability and resistivity in fluid-saturated rock—A re-appraisal

It is affirmed that a consistent development of the equivalent channel model for both fluid permeation and electrical conduction in saturated porous media leads to the expression CR²/F where R is the hydralic radius, F the formation resistivity factor or tortuosity/porosity ratio and C a numerical factor generally around 0.3 to 0.4. This expression is approximately supported by observations reported on granular media and fairly porous rocks. Confirmation of its applicability to low porosity, microcracked rock is still lacking but it would appear to be consistent with measurements on granite in that it indicates that the hydraulic radius (represented by half the mean crack opening width) decreases as the confining pressure is increased. In any application it is important in estimating R and F to take only the connected porosity into account.