Porosity and Permeability of Petroleum Reservoir Rocks || Petroleum Engineering

Porosity of Reservoir Rocks

Porosity is defined as Total pore volume divide by Total Rock Volume.For the clastic  rocks hydrocarbon accumulate in pore space.

1. For Clastic Rock Porosity occurs 
2. For Non Clastic rock Void space occurs.
3. For igneous rock  Fracture  Occurs

Two types of porosity, and these are -

1. Total Porosity or absolute porosity 
2. Effective Porosity

1. Total Porosity:- 

In total porosity or absolute porosity it includes the interconnected pore space as well as dead pore space.

                                                           Total Pore Space volume 

                     Total Porosity =                 Total Volume Rock

2. Effective Porosity 

Effective porosity is only interconnected porosity. 5-10 % lesser than total porosity.

Based on the origin of rocks -

• Primary Porosity/Original Porosity 
• Secondary Porosity/Induced Porosity

1. Primary Porosity/ Original Porosity:-

This pore space generate at the time of deposition of sediment. Primary porosity depends on ----

1.  Size OF Rock Grain
2.  Packing of Rock Grain 
3. Uniformity of Rock Grain 
4. Shape of Rock Grain 
5. Sorting of Rock Grain 

If rock Grain  is Spherically Packed , Porosity is very High.

47 % is higher or maximum porosity for elastic rock. Not Possible to get higher than 47 percent in clastic rocks.

Porosity of rhombohedralically  packing rock is only 25 percent.

Inter-granular porosity is 25 % is an example of primary porosity.

2. Secondary Porosity/ Induced Porosity:- 

This pore generate after the deposition of sediment due to tectonic and geological activity ( Earthquake , generation of fault). Example - 

• Fracture in the igneous rock.
• Fracture  in Carbonaceous rock.
• Fracture in the shale rock.
• Fracture in CBM reservoir. 

Permeability   

It is the fluid transmit ability of the rock. It basically Depends on -

1. Connectivity of pore spaces:-  Higher the connectivity, higher is the permeability.
2. How easily a fluid pass through the porous media.

Permeability are three types ---

• Absolute Permeability.
• Effective Permeability
• Relative Permeability 

1. Absolute Permeability

The porous media is saturated with single phase ( Only Crude oil, gas and water ). Then in which the fluid fluid can passed through porous media. Then it is called Absolute Permeability.

Absolute permeability is rock property.

2. Effective Permeability

If porous media is saturated with two phase, then how easily a fluid passed through porous media in present of other fluid then called effective permeability.

3. Relative Permeability

Effective Permeability

Absolute Permeability

Unit of Permeability 

Unit of permeability is darcy. (K)

For linear flow the negative sign is required.

Direction of Change in pressure and direction of length is different, For linear blow.

Notes:- Data is collected from various university notebook , purpose is to help everyone.

Article written by:-

Ritu Raj Medhi

Founder & president 

Chief Technical and Editorial Officers

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