Losses of Porosity and Permeability in Lithic Sands Assessed with Compaction Experiments: ABSTRACT

Abstract

Compaction experiments with Recent lithic sands indicate that in addition to grain rearrangement, ductile grain deformation can significantly reduce porosity and permeability in sandstones. Compacted artificial mixtures of quartz and potentially labile rock fragments demonstrate, as expected, that the lithic grain content can control the amount of compaction and porosity loss at depth. Using a triaxial deformation apparatus, simulated overburden experiments were conducted with a Recent lithic sand from the Eagle River, Alaska, containing approximately 55% argillaceous sedimentary rock fragments. Additional experiments were conducted with artificial mixtures of quartz grains and varying percentages of shale fragments. Water-saturated samples were compacted at a constant strain rate of 10/sup -4/ under maximum uniaxial stress levels ranging from 1500 to 9000 psi (equivalent to burial depths of 3000 to 18,000 ft). Porosity loss due to compaction was calculated from volume reduction. Vertical permeability for each experiment was measured in situ at the maximum simulated overburden stress level. Results indicate that the porosity of these lithic sands initially declines almost linearly with increasing overburden pressure. At higher pressures (in excess of 5000 psi) the porosity decline gradient is greater for sands with a greater percentage of lithic fragments. This relationship may be attributed tomore » continued porosity reduction due to mechanical deformation of ductile grains. Thin-section analysis of the Eagle River sands indicates that deformation of labile grains is important in reducing porosity to 7% and vertical permeability to 3.2 md at a simulated overburden pressure of 9000 psi.« less