Porosity is percent of rock

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Aquifer • Properties: Porosity, specific yield, specific retention • Potential: Transmissivity, storativity • Types: confined, unconfined • Hydraulic conductivity, Physical Laws controlling water transport Porosity • Porosity is percent of rock or soil that is void of material • n = 100 Vv/V • n = porosity (percentage) • Vv = volume of void space (L3, cm3, m3) • V = unit volume of material including voids and solids How to measure porosity Density of a fluid • • • ρ = m/v (M/L3) m = mass (M) v = volume (L3) Total Porosity • n = 100 [1 – (ρb/ρd)] • n = porosity (percentage) • ρb = bulk density of aquifer material • ρd = particle density of aquifer material Factors affecting porosity • Packing • Grain-size distribution - sorting Grain packing, grain size, and porosity • Cubic packing: n = 47.65% • Rhombohedral packing: n = 25.95% • Grain size mixture => porosity lowered Sediment Classification • Sediments are classified on basis of size of individual grains • Grain size distribution curve • Uniformity coefficient Cu = d60/d10 • d60 = grain size that is 60% finer by weight • d10 = grain size that is 10% finer by weight • Cu = => well sorted; Cu > => poorly sorted d60 d60 d10 d10 d60 d10 d60d10 Porosity of sedimentary rocks • Diagenesis => compaction, removal or addition of material, transformation of minerals by replacement or phase change Porosity of sedimentary rocks • Diagenesis => compaction, removal or addition of material, transformation of minerals by replacement or phase change • Primary porosity – pores between grains • Secondary porosity – fractures in rock • Clastic rocks – n = 3% - 30% • Limestones and dolomites – n = 1% - 30% Porosity of plutonic and metamorphic rocks • Weathering and fracturing – increase overall porosity • Tectonic stresses - fracturing, faulting, folding • Fracturing increases porosity by 2% - 5% • Weathered plutonic rocks can have porosities of 30% - 60% Depth 100 (meters) Porosity of volcanic rocks • • • • Degassing products –> holes in the rock Shrinkage cracks -> joints Basalt – 1%-12% Pumice – glassy rock formed from a magma with high gas -> can be as high as 87% • Pyroclastic deposits – Tuff – 14% - 40% • Ash – 50% [...]... d60d10 Porosity of sedimentary rocks • Diagenesis => compaction, removal or addition of material, transformation of minerals by replacement or phase change Porosity of sedimentary rocks • Diagenesis => compaction, removal or addition of material, transformation of minerals by replacement or phase change • Primary porosity – pores between grains • Secondary porosity – fractures in rock • Clastic rocks... and dolomites – n = 1% - 30% Porosity of plutonic and metamorphic rocks • Weathering and fracturing – increase overall porosity • Tectonic stresses - fracturing, faulting, folding • Fracturing increases porosity by 2% - 5% • Weathered plutonic rocks can have porosities of 30% - 60% Depth 100 (meters) Porosity of volcanic rocks • • • • Degassing products –> holes in the rock Shrinkage cracks -> joints... water, wave action … => higher porosity • Poor sorting => glacial action, landslides … => lower porosity • Grain shape => sphere, rod, disk, book … Sediment Classification • Sediments are classified on basis of size of individual grains • Grain size distribution curve • Uniformity coefficient Cu = d60/d10 • d60 = grain size that is 60% finer by weight • d10 = grain size that is 10% finer by weight • Cu... plutonic rocks can have porosities of 30% - 60% Depth 100 (meters) Porosity of volcanic rocks • • • • Degassing products –> holes in the rock Shrinkage cracks -> joints Basalt – 1%-12% Pumice – glassy rock formed from a magma with high gas -> can be as high as 87% • Pyroclastic deposits – Tuff – 14% - 40% • Ash – 50%
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