Seal rocks and traps for petroleum

Azizi Myrie March 23,2023

Oil shale trap/seal rock.

The seal (cap rock) has to be a low permeability component to stop hydrocarbons from the reservoir from escaping. Evaporites, chalks, and shales are common types of seals.

The evaluation of a seal's permeability, lateral extent, and vertical thickness are all part of the analysis process.

Fluoride Injection Permeability: When the rock has been evacuated and submerged in mercury, the mercury's pressure is gradually increased, driving the mercury into the pores of the rock.

Hence, the permeability and porosity may be identified.

Shales:

• The most frequent seals are shale, while the best seals are evaporites.
• Shales often have pores, however, due to their tiny grain size
• possess extremely strong capillary forces that inhibit fluid flow.

Traps

Petroleum traps are underground traps made up of permeable reservoir rock and cap rock with limited permeability. There are other variations of this mix of rocks, but they all work to stop oil and gas from rising through the reservoir rock. Once in the reservoir rock, the natural gas and oil continue to move upward via the pore spaces of the rock until a cap rock or other kind of seal blocks their upward migration. Shale, low-permeability sandstones and carbonate rocks often make up the low-permeability cap rocks.

Traps may be divided into two main groups according to how petroleum gathers in them. Structural traps and stratigraphic traps are the two basic categories.

These are traps created by structural deformation and are amongst the most important types of traps.

Stratigraphic traps are due to changes in the permeability of the sediments. 

References:

“Hydrocarbon Seal and Migration- Incorporated Research Institutions for Seismology.” Hydrocarbon Seal and Migration- Incorporated Research Institutions for Seismology, www.iris.edu/hq/inclass/lesson/hydrocarbon_seal_and_migration.

“Oil Shale.” Oil Shale, education.nationalgeographic.org/resource/oil-shale.

“Oil And Gas Traps - Energy Education.” Oil And Gas Traps - Energy Education, energyeducation.ca/encyclopedia/Oil_and_gas_traps#:~:text=Stratigraphic%20Traps,-These%20traps%20are&text=When%20the%20sediment%20that%20creates,the%20oil%20and%20gas%20inside.