Understanding Geological Factors for Predicting Abnormal Pressure in Well Planning

Drilling for oil and gas can be a hazardous endeavor, with unexpected pressure changes posing a significant threat. Fortunately, geological data can be a powerful tool in predicting these risks and ensuring a safe and successful operation. This article explores some of the most common geological features that can lead to abnormal pressures and how to identify them based on available data.

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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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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.