Effective sand permeabilities can be ascertained from core analysis if thelaboratory data are compensated to allow for the presence of connate orresidual water. Such adjustments can be made by applying empirically derivedcorrection factors. Effective sand permeabilities can be estimated also from analytical studiesof field depth-pressure measurements. In one method the time rate of pressurebuild-up after a well is shut in from steady-state flow is required, and in theother the direct measurement of a steady-state rate of flow and thecorresponding equilibrium pressure. The results of the investigation discussed in this paper demonstrate thatthese methods for determining mean effective sand permeabilities can becorrelated. Introduction In recent years many investigators have demonstrated the practical value ofan accurate knowledge of the physical and dynamical characteristics ofreservoir sands containing oil and gas. Of these factors, which serve tocompletely define a porous medium as a container or carrier of fluids, thedynamical characteristics are of particular interest to the production engineerbecause they afford a direct measure of the rate at which the oil or gascontent of a reservoir will become available. The constant that definesdynamically the porous medium as the carrier of a homogeneous fluid in viscousmotion is the "permeability." Core-Analysis Method The generally accepted practice in compiling permeability data has been toanalyze in the laboratory core samples taken in the course of drilling throughthe productive horizon, and to obtain the mean measure of the productiveability or permeability for the interval open to production by graphicalintegration of the permeability profile. An average permeability ascertained in this manner, however, is useful tothe production engineer only for comparisons of wells drilled in the samehorizon, as permeabilities determined in the laboratory are measures of onlythe ability of a porous medium to transmit a single fluid. As a result of manyinvestigations, it has been shown, however, that under actual reservoirconditions water is coexistent with the petroleum and that its presence greatlyreduces the permeability of the sand to oil. T.P. 1464