Effective and Relative Permeability

When there is only one type of fluid flowing through porous media, the permeability for this case is called “absolute permeability.” However, when there is more than one type of fluids present in a rock, a permeability of each fluid to flow is decreased because another fluid will be moving in the rock as well.  A new term of permeability called “effective permeability” is a permeability of a rock to a particular fluid when more than one type of fluid is in a rock.

Reservoir consists of three fluids (gas, oil, and water) so these are commonly used abbreviations for effective permeability for each fluid.

kg = effective permeability to gas

ko = effective permeability to oil

kw = effective permeability to water

Normally, it is common to state effective permeability as a function of a rock’s absolute permeability. Relative permeability is defined as a ration of effective permeability to an absolute permeability of rock. The relative permeability is widely used in reservoir engineering. These functions below are the relative permeability of gas, oil, and water.

Relative permeability to gas – krg = kg÷k

Relative permeability to oil – kro = ko÷k

Relative permeability to water – krw = kw÷k


k = absolute permeability

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What is Porosity?

Porosity is one of rock important rock properties and it is a measure of pore space in a rock.

Figure 1 – Porosity

(Ref: http://www.tulane.edu/~sanelson/images/pores.gif)

Figure 1 shows the illustration of porosity and it can be seen that grain size and distribution can affect porosity of rock.

Porosity (ɸ) is mathematically expressed as a ratio of total void space with a rock to a total volume of rock.

Porosity (ɸ) = (Vp ÷ Vb) × 100


Vp = pore volume

Vb = bulk volume of rock

Porosity (ɸ) is shown in percentage form. Continue reading

5 Steps To Heaven in Petroleum Geology

The 5 Steps to Heaven, which are source, migration, reservoir, seal and trap, is one of the most important concepts of petroleum geology. This tells us how petroleum was formed, migrated and trapped in a reservoir. Please note that the 5 Steps to Heaven is valid for conventional petroleum resources.



Typically, organic matter from animals and plants is oxidized and turned an organic matter into carbon dioxide and water. However, if organic matter is buried rapidly, it may be preserved and can be turned into petroleum. These following conditions enhance organic matter preservation.

  • High sedimentation rate
  • Fine grain size so oxygen will not be able to penetrate and oxidize the organic matter
  • Anoxic bottom water

These conditions are mostly found in shale and fine limestone, which are common source rocks. Continue reading

Basic Understanding about 3D Seismic for Petroleum Exploration

3D seismic is one of the most important techniques to help geologists and engineers to find out where possible hydrocarbon is below thousands of feet below the earth surface. Without 3D seismic technology, many oilfields cannot be discovered.

We’ve found this excellent which will give you some ideas of how 3D seismic works in order to help us find oil and gas. Additionally, we also provide the full video transcript to help someone to learn about this topic. We wish you would enjoy watching and learning from this VDO.


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