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What is "Unconventional" Oil and Gas?

"Unconventional" oil and gas is not chemically different from "conventional" oil and gas. The distinction stems from their position underground or from the unusual nature of their reservoirs. These conditions require the use of new, often complex, extraction methods. Below is a simplified summary of these oil and gas resources.

Aerial view of the oil sands extraction site operated by Canada-based Syncrude, located north of Fort McMurray in Alberta Province.© AFP

Oil and gas deposits take millions of years to form. Following a period in which plant matter is gradually buried, oil and gas form very deep underground in source rock. Then they begin their migration (hydrocarbons)The stage in oil formation when the hydrocarbons are gradually expelled from the source rock and rise to the surface... toward the surface, sometimes accumulating in porous, permeable reservoir rocks when sequestration conditions are favorable.

Over the past decades, oil and gas companies have first focused on developing the "easy" reservoirs with the greatest porosity and permeability, followed by reservoirs located deeper underground or in hard‑to‑reach areas and, lastly, the source rock itself. At each stage, the technologies used have become increasingly complex and efficient.

The breakdown below is divided into liquid and gaseous preservation (hydrocarbons)The final phase in petroleum system formation, after a deposit has accumulated..., distinguishing each time which resources come from reservoir rock and which from source rock1.

1. Unconventional liquid hydrocarbons

Oils found in reservoir rock Located beneath the cap rock, porous and permeable rock in which large amounts of oil and gas accumulate...

Oils found in source rock Sedimentary rock containing large amounts of organic matter and found in deep sea...

While reservoir rock is usually porous, source rock is more often clayey with a plate-like appearance, hence the name "shale".

2. Unconventional gaseous hydrocarbons

"Unconventional" oil and gas is not chemically different from "conventional" oil and gas.

Gas found in reservoir rock

Tight gas: gas found in the same type of reservoir rock as tight oil, i.e., with low porosity and permeability. The same methods – hydraulic fracturing and horizontal drilling – are used for extraction.

Gases found in source rock

Methane hydrate

In a category of its own, methane hydrate is a mixture of water and methane that accumulates in ocean sediments near the sea floor and in permafrost in Arctic regions. Under certain pressure and temperature conditions, methane hydrate crystallizes, forming a solid. However, extracting these crystals is costly and complex.




(1) IFP-EN (in French)