تخلخل

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

1. Primary (original) Porosity

   Developed at time of deposition

2. Secondary Porosity

   Developed as a result of geologic process occurring after deposition

3. Total Porosity

   φt = total pore space/Vb = (Vb - Vm)/Vb

D. Effective Porosity

φe = interconnected pore space Vb

1. Clean sandstones: φe = φt

2. Carbonate, cemented sandstones:

φe <φt