I) Definition
A measure of the pore space available for the storage of fluids in rock
In general form:
Porosity = φ = Vp = Vb - Vm /(Vb +Vb)
where:
φ is expressed in fraction
Vb = Vp + Vm
Vb = bulk volume of reservoir rock, (L3) Vp = pore volume, (L3)
Vm= matrix volume, (L3)
II) Classification
Primary (original) Porosity
Developed at time of deposition
Secondary Porosity
Developed as a result of geologic process occurring after deposition
Total Porosity
φt = total pore space/Vb = (Vb - Vm)/Vb
D. Effective Porosity
φe = interconnected pore space Vb
Clean sandstones: φe = φt
Carbonate, cemented sandstones:
φe <φt