3. Defination:
The ratio of the pore volume in a rock
to the bulk volume of that rock.
Denoted by φ.
Express in Percent.
Mathematical Form: φ = Vp/Vb
6. Types of porosity
There are two types of porosity
1) Primary porosity
2) Secondry porosity
1) Primary porosity
The porosity of the rock that formed at the time of its deposition.
2) Secondry porosity
Develops after deposition of the rock.
For example:
Fracture spaces formed in fractured reservoirs
7. Further types of porosity
They are further subdivided into
1) Total porosity
2) Effective porosity
3) Microporosity
4) Mesoporosity
5) Macroporosity
1) Total Porosity
The ratio of the entire pore space in a rock to its bulk volume.
2) Effective Porosity
The measure of the void space that is filled by recoverable oil and gas
φ = Vol. of interconnected pores + Vol. of deadend
Total or bulk vol. of reservoir rock
In very pure sandstone Total porosity is equal to Effective porosity
8. 3) Microporosity
In solids , the term 'microporosity' refers to pores smaller than 2 nm
in diameter.
4) Mesoporosity
In solids , the term 'mesoporosity' refers to pores greater than 2 nm
and less than 50 nm in diameter.
5) Macroporosity
In solids , the term 'macroporosity' refers to pores greater than 50
nm in diameter.
9. Determination of Porosity
1) Direct method
2) Water evaporation method
1) Direct methods
Determining the bulk volume of the porous sample, and then
determining the volume of the skeletal material with no pores .
pore volume = total volume − material volume.
2)Water evaporation method
pore volume = weight of saturated sample − weight of dried
sample)/density of water