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.

 Reservoir rocks for petroleum

Azizi Myrie March 23,2023

Containing granules the size of sand Colors that are often pale beige to tan but can also be dark brown to rusty red. Porosity and permeability are the main factors of reservoir rocks, in sandstone ranging from 10% to 30%. Sorting is a major factor in determining intergranular porosity (primary porosity).

A crucial characteristic of a reservoir rock is porosity. Nevertheless, permeability is the essential characteristic for it to be an effective reservoir rock. Both permeability and porosity are geometric characteristics of rocks that result from their lithologic (compositional) origin. The age of the rock is less important when discussing reservoir rocks than its physical composition and textural attributes (geometric elements like the sizes and shapes of the component grains and how they are packed).

In actuality, sandstones are home to the great bulk of the massive oilfields and tremendous oil output. Sandstones frequently have very high primary and secondary permeability values. For instance, the bulk of the oil and gas produced in Russia comes from clastic reservoir rocks. Moreover, American production has made substantial use of clastic reservoir rocks. There are a few notable exceptions, though. To give two examples, the Permian Basin in southwestern America and the vast oilfields in the Middle East are both carbonate (limestone) reserves.

Picture above represents the the sandstone oil reservoirs in Russia.

The original sandstone reservoir's quality depends on the location of the material's source, how it was deposited, and the surrounding conditions. Sandstone reservoirs typically have a thickness of 25 meters, are linear and lenticular in space, and cover an area of fewer than 250 km2. They range in age from the Pliocene, which is the youngest, to the Cambrian, which is the oldest (in Algeria) (Caspian region in Ukraine). Two-thirds of the sandstone reservoirs in the USA date back to the Cenozoic era.

References

http://www.dnr.louisiana.gov/assets/TAD/education/BGBB/4/rocks.html#:~:text=Answer%3A%20Dolomites%20are%20normally%20less,Voids%20that%20hydrocarbons%20can%20fill. www.dnr.louisiana.gov/assets/TAD/education/BGBB/4/rocks.html#:~:text=Answer%3A%20Dolomites%20are%20normally%20less,voids%20that%20hydrocarbons%20can%20fill.

Hindawi, et al. “Overview of Lower Cretaceous Achimov Formation: Physical Properties and Their Distribution Pattern in West Siberian Basin, Russia.” Overview of Lower Cretaceous Achimov Formation: Physical Properties and Their Distribution Pattern in West Siberian Basin, Russia, 8 Apr. 2021, https://doi.org/10.1155/2021/5560117.

“Reservoir Rocks.” PETROLEUM GEOLOGY, petgeo.weebly.com/reservoirrocks.html.

Source rocks for petroleum 

Azizi Myrie March 23,2023

This Marcellus shale exposure in central New York contains the grey-colored Cherry Valley limestone between the Union Springs and Oatka Creek shales.

Petroleum source rock is fine-grained sediment containing enough organic materials to create and release sufficient hydrocarbons to form a commercial accumulation of oil or gas. The most prevalent source rocks are shales and lime mudstones, which contain many organic materials. Any rock that may develop and release enough hydrocarbons to form an accumulation of oil or gas is considered a petroleum source rock. According to oil generation, source rocks are divided into three types :

Immature source rocks that have yet to produce hydrocarbons.

Mature source rocks in the generation stage.

Post-mature source rocks have already produced all crude oil-type hydrocarbons.

Potential source rocks are immature sedimentary rocks that, at a higher maturity level, might produce and release hydrocarbons.

Potential source rocks are sedimentary rocks that may have produced and released hydrocarbons but whose source potential has not yet been assessed.

Sedimentary rocks are good sources of hydrocarbons because they have produced and released them in the past.

The primary criteria used to assess the hydrocarbon source are the quantity (organic richness), quality (kerogen type), thermal maturation production capability, and distribution of organic matter in the rock. The organic matter composition of the source rock samples (shale, limestone, or marl) can be assessed directly. Yet, indirect approaches based on wireline data allow continuity of sampling of vertically diverse shale sections, are cost-effective and have easy access to data.

Reference

Al-Areeq, Nabil Mohammed. “Petroleum Source Rocks Characterization and Hydrocarbon Generation.” Petroleum Source Rocks Characterization and Hydrocarbon Generation | IntechOpen, 7 Feb. 2018, https://doi.org/10.5772/intechopen.70092.

“Marcellus Shale in Central New York Showing Cherry Valley Limestone | U.S. Geological Survey.” Marcellus Shale in Central New York Showing Cherry Valley Limestone | U.S. Geological Survey, 5 Mar. 2015, www.usgs.gov/media/images/marcellus-shale-central-new-york-showing-cherry-valley-limestone.

 source rocks for petroleum.

Azizi Myrie March 23, 2023

Source rocks –the basics 

What is a Source Rock? 

1. It must have sufficient organic matter 

2. It must have organic matter of the right type 

3. It must have been buried to a sufficient depth to become mature 

Hello, folks! My name is Azizi Myrie, and I am a University of the West Indies Mona campus senior studying education technology (EDTK3004). Irie with Myrie's mission is to inform people about various facets of the petroleum sector. In addition to starting this blog for an assignment, I feel it's my duty as a budding geologist and botanist to utilize my platform to inform others about the rocks used as sources for petrology. You won't regret to stay tuned!