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

Hydrocarbon Migration

Hydrocarbon migration is a process that petroleum migrates from source rocks into reservoir. In petroleum geology, hydrocarbon migration is divided into two parts, which are a primary migration and a secondary migration.

Primary Migration

The primary migration is when petroleum comes out of source rocks. The mechanisms behind the expulsion of hydrocarbons from source rocks into reservoir rocks are not clearly understood. There are several questions which nobody can clearly answer as (AAPG Wiki, 2015);

  • How does oil escape from the source rock?
  • Does oil migrate out of the trap?
  • Why are there marked differences in oil gravity, wax content, and sulfur content in lateral and stratigraphically successive sands?
  • Why are there differences in water salinity for multiple sands in one structural trap?
  • What is the role of faults in transporting and trapping hydrocarbons?
  • Why are there barren sands within sequences of productive sands?
  • How is the cross-formational flow of hydrocarbons accomplished?
  • Does the form change during migration and, if so, which form is dominant under what conditions?
  • How can we estimate the timing, volumes, and compositions of transported hydrocarbons?

Figure 1 shows the diagram of a primary and secondary migration.

Figure 1 – Primary and Secondary Diagram

(Ref Image: http://www.ngdir.ir/Data_SD/GeoLab/Pics/GeoLabPic_865_2.jpg)

Secondary Migration

Secondary migration is the movement of hydrocarbon through reservoir rocks such as limestones and sandstones which are permeable. Hydrocarbon can travel through these rock as distinct phases in the upwards direction where there is a decrease in hydrostatic pressure.

Three forces relating to how hydrocarbons move in porous rocks are a gravity force, a buoyancy force and a capillary force. In order for hydrocarbons to migrate, the buoyancy force must overcome gravity and capillary pressure. Hydrocarbons will naturally flow through reservoir rocks until they are stopped by impermeable structures. Then they begin to accumulate. If there is no trap, hydrocarbon will reach surface and this is called “oil seepage.”

Hydrocarbons accumulating in reservoirs will separate as layer sequences – gas on top, oil in the middle and water at the bottom (Figure 2).

Figure 2 – Hydrocarbons in Reservoirs

(Ref Image http://1.bp.blogspot.com/-_U6qLaOf49s/VIHgXlKG5SI/AAAAAAAACnk/zMaHaKYmsRc/s1600/natural_gas172.jpg)


Richard C. Selley, 2014. Elements of Petroleum Geology, Third Edition. 3 Edition. Academic Press.

Norman J. Hyne, 2012. Nontechnical Guide to Petroleum Geology, Exploration, Drilling & Production, 3rd Ed. 3 Edition. PennWell Corp.

Richard C. Selley, 1997. Elements of Petroleum Geology, Second Edition. 2 Edition. Academic Press.

Transform Organic Matter into Petroleum

This article will explain the overall of how to transform organic matter into petroleum. Chemical processes will take place in order to transform organic matter preserved in source rocks into petroleum. This can be called a cooking process. Three phases regarding maturation of the organic matter to form petroleum are diagenesis, categenesis and metagenesis.

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Organic Matter to Form Source Rock

Oil and gas that we are drilling today comes from a biogenic origin and it is formed with proper time and temperature. Organic matter is one of the most important parts of hydrocarbon generation. This topic will give you an overview of how organic matter will be transformed to hydrocarbon.


Starting with plants and algae, take carbon (CO2) from the atmosphere and process it to form glucose and this starting process is called photosynthesis. Glucose is transformed into more complex organic compounds. Trees, for example will grow bigger because they use photosynthesis to convert into energy. When animals and trees die, the organic matter is typically oxidized and this will create CO2 and put water back into environment again.  However, in some situations when organic matter is buried quickly in areas where there is no oxygen, the organic matter may be preserved. If the organic matters are buried in proper conditions, petroleum may be formed. Continue reading

Geological Time Scales

Geological time scales help us to know the age of formations and three types of time scales are relative, absolute time and magnetic polarity scales. Relative time scale relates to an order in which a specific rock sequence occurs, but absolute time is an actual time that is derived from the chemical half-life of minerals in rocks. Magnetic polarity uses a concept of magnetic sequences to age the rocks.

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