Oil and Gas Traps

Oil and Gas Traps

Oil and Gas in Rocks

You may have heard that oil is found underground in "pools", or "lakes", or "rivers". Maybe someone told you there was a "sea" or "ocean" of oil underground. This is all completely wrong, so don't believe everything you hear.

Almost all oil and gas is found within the tiny spaces in sedimentary rocks, mainly sandstone and coarse-grained limestones. Imagine that a sponge is a hunk of sandstone or limestone. The sponge is full of holes, or "pores", that can contain water or oil or gas. Limestone and sandstone, even though hard, also contain lots of holes. The holes are much tinier than sponge holes, but they are still holes, called "porosity". The oil and gas become trapped in these holes, and they stay there, for millions of years, until Petroleum Geologists come to find it and get it out.

When you hold a piece of sandstone containing oil in your hand, the rock may look and smell oily, but the oil usually won't run out, and you can't squeeze sandstone like a sponge! The oil is trapped inside the rock's porosity.

How do oil and natural gas get into the rocks in the first place? There are several ideas about how this happens, but one idea is very popular , and it is called...

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