Understanding the oil and gas industry – Part 1

Geology in the oilfield

Geologists who do the leg work for discovering oil fields will cringe at my less-than technical description of what happens deep underground for oil to be created, but I’ll still give you a brief summary of how I understand it.

When first setting out to see if oil is feasibly underground, geologists look for three things: a source rock, reservoir rock and cap rock. If you read my previous post on Vocabulary you should know, you’ll have read the definitions for these three rocks. If not, here’s another look at what they are.

Let’s first understand what happens underground for oil to be formed.

Kerogen, a naturally occurring organic soluble material that produces hydrocarbons, is found in a source rock. Three types of kerogen produce hydrocarbons. The first one, which produces liquid oil is made of marine algae and plankton. The second, which produces liquid oil and/or gas is made of marine and terrestrial plant and animal material; and the third, which produces mainly coal is made of terrestrial plant material.

If buried deep enough in the earth, over time, these kerogen-laden rocks will be cracked with heat into smaller hydrocarbon molecules which make up liquid oil and gas.

In order for this oil or gas trapped in the source rock to be of any use though, it must first come into contact with a reservoir rock, a rock that has enough porosity and permeability for oil to pass through it and up to an oil well if tapped. Sandstone rocks are the most common type of reservoir rock that meets this criteria. Once these two factors are in place, the third rock geologists look for to point towards an oil find is a cap rock, which will trap the oil and gas below ground so that it cannot rise to the surface over time and leak into the earth – leaving no oil to extract.

To find a cap rock, geologists look for a fault line on the surface near where their prospective field is to indicate that a cap rock may be trapping oil. The whole field of geologists searching for oil is highly technical and they use a host of fascinating tools, surveys and technology to ascertain if oil could indeed be underground – that I can’t do justice here. Just take my word that these professionals really know what they are doing and it’s highly scientific…unlike my description above. You understand now why science was never a strong suit.

Next we’ll take a look at the exploration and drilling side of the oil and gas industry and what it entails.

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