Estimating Aquifer Permeability from Formation Resistivity Factors

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Abstract
A comparison of permeability results for individual producing zones obtained from pumping tests and flow‐meter logs showed a good correlation to calculated corresponding formation resistivity factors (F). Where F = a/Øm or F = R0/RW, and porosity (Ø) is obtained from the neutron log, m is the formation cementation factor, Ro is saturated formation resistivity from normal electric logs, and Rw is formation pore‐water resistivity. Unlike formations containing saline water where the electrical current is conducted through the pore fluid, in fresh‐water aquifers the electrical current appears to be conducted along the grain‐aqueous interface by surface conductance rather than through the grain or pore fluid. Surface conductance of the current serves to increase the current path length which is recorded as an increase in the measured saturated resistivity (Ro). The current path direction and length through the formation is directly related to the shape, diameter, and sorting of the grains, geometric packing arrangement, and degree of matrix cementation. Fortunately, all of these factors that serve to increase the current path [which in turn directly increase saturated formation resistivity (Ro) and F] also are factors that increase formation permeability.Relative changes in F values can be matched with known permeabilities from aquifer tests and flowmeter logs to quantify the relative productivity of the various zones analyzed. Once this relationship is established, F values can be used to assign relative permeabilities within a single borehole or from borehole to borehole for a given geographical area.This method has been successfully used to estimate permeability in both unconsolidated sands and Tertiary carbonate aquifers in the southeastern Coastal Plain of the United States.

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