Influence of Texture on Porosity and Permeability of Unconsolidated Sand'D. C. BEARD" and P. K. WEYL'Midland, Texas 79701, and Stony Brook, New York 11790
Abstract An investigation has been made of the rela-tions among porosity, permeability, and texture of arti-ficially mixed and packed sand, to determine the ap-proximate porosity and permeability values to be ex-pected for unconsolidated sand of eight grain-sizesubclasses and six sorting groups. The sand sampleswere prepared so that the weight fractions were dis-tributed normally about the median grain size. Poros-ity values were determined for two packings, desig-nated as "dry-loose" and "wet-packed." Porosity datafor "wet-packed" sand samples remain about thesame for changes In grain size of a given sorting, butdecrease from an average of 42.4 percent for ex-tremely well-sorted sand to 27.9 percent for verypoorly sorted sand. These experimental data agreewithin 5 porosity percent with framework porosity val-ues obtained for natural packing of 25 Holocene bar-rier-Island sand samples of a limited size-sortingrange, and appear to be representative of minimumporosities expected for natural packing of most uncon-solidated, clay-free sand.The 48 artificially mixed and wet-packed experimen-tal sands selected for porosity measurement also wereused to determine permeability. Inasmuch as thereare some irregularities In the experimental datacaused by the Inability to pack each sample uniformly,an average adjusted permeability value has been cal-culated. The average adjusted permeability values be-come progressively lower with decreasing grain sizeand poorer sorting, and agree well with permeabilityvalues computed by the Krumbein and Monk formulafor most grain-size and sorting classes.Reference photographs or visual textural compara-tors enable a rapid estimation of grain shape, round-ness, size, and sorting. Grain-size-sorting compara-tors, representing photomicrographs of thin sectionsof the porosity and permeability test samples, are es-pecially useful In estimating original textural parame-ters from thin sections of severely compacted andsilica-cemented sandstones.
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