Porosity is percent of rock

• Properties: Porosity, specific yield, specific retention.. • Hydraulic conductivity, Physical Laws controlling water transport... How to measure porosity... Grain packing, grain size,

• Properties: Porosity, specific yield, specific retention.

• Potential: Transmissivity, storativity.

• Types: confined, unconfined.

• Hydraulic conductivity, Physical Laws controlling water transport.

• V v = 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 – (ρ b /ρ d )]

• n = porosity (percentage).

• ρ b = bulk density of aquifer material

• ρ d = particle density of aquifer material

Factors affecting porosity

• Packing

• Grain-size distribution - sorting

Grain packing, grain size, and

Processes affecting grain sorting

• d60 = grain size that is 60% finer by weight.

• d10 = grain size that is 10% finer by weight

• Cu = 4 => well sorted; Cu > 6 => poorly sorted

d60

d10

d10

d60

d10

d10

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%

Porosity of volcanic rocks

• Degassing products –> holes in the rock

• Shrinkage cracks -> joints