- Petroleum is the word for solid, liquid, and gas hydrocarbons (compounds with hydrogen and carbon).
- Solid hydrocarbons are coal, liquid ones are oil, and gas ones are natural gas.
- Crude oil is naturally occurring petroleum.
- Petroleum with hydrogen sulfide (H2S) is called sour, such as sour oil or sour gas.
- Oil that won’t flow or can’t be pumped or extracted unless it’s heated or diluted is called bitumen.
Where is it and how did it get there?
Petroleum doesn’t come from big underground lakes but is trapped in holes or cracks of certain rocks such as sandstone or limestone, like in a sponge.The most common explanation for how it got there is that long ago plants and animals died and their remains were buried deeper and deeper over time. As the depth increased, heat and pressure turned their natural chemistry into hydrocarbons. Different types of plants and animals under different pressures result in either coal or oil or natural gas.
How do they find it?
Usually, exploration is done using seismic surveys. A crew puts down receivers called geophones on the ground and explosions
or vibrations are created on the surface (or in offshore exploration, compressed air is used). The geophones record the energy
reflected back from the rock layers below as seismic waves. Earth scientists then study the information and can tell where
traps of oil and gas may be, based on the types of rocks down there.
How do they get it out of the ground?
Drilling
After seismic exploration, if the company decides it is worth it to check it out, they will drill a well. A drilling rig (and there can be many types and sizes) comes and a revolving steel bit at the bottom of a string of connected pipes grinds a hole through the rock layers to get to the pockets of oil and natural gas. Usually they drill straight down, but they can also do slant or horizontal drilling. From this hole, called a wellbore, they take back information to the company including cuttings, chip samples, cores, etc., and the company will test to see if the well would make money for them.
Completions
If the company decides the well is worth continuing with, then the drillers leave and a service rig comes to bring the
petroleum to the surface. Service rigs—either attached to a truck or free standing—can also be different sizes
and types depending on the kind of well it is. Many other service providers, such as wireliners or snubbers, also come to
the wellsite (sometimes called a lease) to help with special work that needs to be done.
The first thing to do is cement in a big, long steel tube called casing to line the wellbore drilled by the drillers. This keeps junk out of the wellbore. Then they hang production tubing inside that casing and connect it to a wellhead at the top, so they can control the rate at which the petroleum comes to the surface.
Of course they can’t get petroleum out of a sealed concrete hole, so the next step they do is perforation: making small holes in the cement casing with explosive charges that shoot metal rods through the casing into the reservoir. Existing reservoir pressure or simple pumps can then be used to bring the petroleum to the surface. Because oil is gooey, it usually needs pumping—and you may have seen those pump jacks around, bobbing up and down in farmers’ fields, for example. Natural gas, however, can be under a lot of pressure underground, and so great care is taken at the wellhead to prevent a blowout or escaping toxic gases.
However, the petroleum may not just flow to surface on its own, but need some help. This can be stimulated by pumping acid in the reservoir to dissolve some rock to make it easier for the petroleum to get out of that rock. Or they can do something called fracing (FRAK-ing), where fluid is pumped down under pressure to fracture the rock and other material (such as sand) is pumped down to prop those new fractures open so the petroleum can get out of them. If there isn’t enough pressure in the reservoir, water or natural gas can be injected to boost it. Or natural gas liquids or carbon dioxide can be injected to help make the oil thinner so it flows more easily.
In the oilsands in Alberta, a very different method is used where the sand is mined instead of drilled and then agitation or steam can be used to separate the bitumen from the sand.
After the petroleum is brought to surface, oil companies have to get it to users.