This is a barrel of crude oil - it holds about 42 US gallons or about 159 liters. Each day the world consumes 88 million of them - 19 million of which are used right here in the US of A. For 150 years now, we've been living in a petroleum world. Most experts agree that over time, humans have consumed more than 1 trillion barrels of oil.

How much recoverable oil is left in the ground is the subject of great debate among energy experts but rough estimates suggest that the number is between 2 and 4 trillion barrels. But in order for those 2 to 4 trillion barrels of oil to be any use to us, we first need to find it and second, get it out of the ground. Neither of those things are easy and they're getting more difficult.

Fossil fuels, whether you love them or you hate them, you use them - like a whole ton of them in fact. You're using them right now to keep your lights on and to watch me on your computer so you might as well understand how we find it, how we get it and how much we have left, otherwise you might just be left in the dark.

[Intro]

Before we deal with the "How?" part of petroleum science, we should probably first ask "How much?" because how much oil we think, or fear, is left is influencing how and where we're looking for it.

This brings us to a little thing called 'Peak Oil'. Peak Oil is the point at which we've reached the maximum rate of global oil production. This idea was first formulated in 1956 by Shell Oil employee M. King Hubbard, who correctly predicted that oil production in the US would reach its peak around 1970. He theorized that it takes about 40 years from the peak of oil discovery in a given country to reach peak rate of production.

In the US, discovery peaked in the early 1930's, but on a global scale, oil discovery peaked in the 1960's which is why since the early 2000's, people have been freaking out about the idea that humanity may never produce as much oil as it does today.

Obviously, we're dealing with a finite resource here, so there will come a day when it will run out, but Hubbard's theory of Peak Oil has proven incorrect on a worldwide scale mostly because he didn't foresee the enormous changes in how we discover and extract oil. 

Today we're finding oil in places we never thought it existed and in areas thought to have dried up long ago. And we're extracting it using methods and technologies that weren't around when your parents were your age.

To understand the science of it though, you gotta go back maybe like a couple of hundred million years.

Oil and natural gas are formed by the breakdown of organic materials under really high pressure and temperature in sedimentary rock. Most of the material came from the remains of zooplankton and algae that lived in the oceans between 10 and 600 million years ago. When they died, their carbon-rich bodies sank to the bottom of the ocean. As they decayed in deeper and deeper layers of oxygen-starved sedimentary rock, the heat and pressure eventually distilled the biomass into either oil or gas. And what we're really after in these substances is their key ingredients, called hydrocarbons. Like the name tells you, these compounds like methane, ethane, propane and so on, contain only hydrogen and carbon, and when they're burned in the presence of oxygen, they give off lots of heat. 

Over time, the liquid version of this hydrocarbon mixture, petroleum, migrates up into porous layers of rock - usually limestone or sandstone. This is where most oil and gas becomes trapped thanks to impermeable layers of rock like granite or marble above it.

When we talk about conventional methods of extracting oil, we of course mean drilling, and for a formation to be worth drilling, it needs to have at least a couple of qualities. One is enough permeability. That is the ability for a fluid to pass through it, to allow the oil to flow easily into a well. It also has to have enough open spaces in the rock to hold fluid, which is called its porosity.

Now the reality is that most of the big, easy deposits with these traits that we know about - the low hanging fruit of the petroleum world - have been discovered and exploited. Finding new ones requires better equipment and more money and yes, more energy.

One way that's improved a lot in recent years is the use of instruments called gravimeters to measure tiny changes in the Earth's gravitational field. Sedimentary rocks usually get denser so have stronger gravity the further down you go, but folds or faults in the rocks can create big pockets of lower density that could be where oil is hanging out. Gravimeters can find those pockets, which helps exploration crews narrow their searches.

Geologists also often use magnetometers to detect tiny changes in the Earth's magnetic field because it turns out that the magnetic field too changes when oil is around. Where oil and gas are deposited, rocks are less magnetic than the surrounding rock, so through aerial surveys, magnetometers can detect some of these weak spots to give oil prospectors some promising leads.

The most common method of finding oil, however, is through seismology. By creating shockwaves and measuring how fast they travel through layers of rock, geologists can gauge their density. It's like the same concept as an ultrasound scan at your doctor's office or an echo-sounder used by ships.

On land, seismic waves are generated using explosives or a specially designed vehicle known as a Vibroseis or thumper truck. The trucks use what is called a 'seismic vibrator' - I'm just gonna let that phrase sink in for a second - to create a shock wave on the ground. When using explosives, geologists dig boreholes up to 25 meters deep and detonate a small charge. In both cases, detectors called geophones are used to measure the shockwaves.

Oil hunters can use this technology underwater as well. In that case scientists use compressed air guns on a boat, instead of giant vibrators, to create the sound waves. The sound waves penetrate the layers of rock below the sea bed and are reflected back.

Now all these methods are great at finding rock formations with enough permeability and porosity to hold oil, but with demand always rising and Peak Oil fears, we've started going hard after the unconventional stuff. Experts call them 'Tight Oil' and 'Heavy Oil'.

Heavy Oil is oil that is as dense or denser than water - usually oil is a lot less dense than water, which is why it floats on top of water.

Tight Oil, meanwhile, is found in formations where the rock's porosity and permeability are really, really low. There's oil in there, but its not flowing like the easier places we used to drill.
Here in the US, Tight Oil is the reason crude oil production grew by more than 1 million barrels a day in 2012, the largest increase in our country's history. The two largest Tight Oil formations - the 'Eagle Ford' in South Texas and The Bakken in North Dakota and Montana, contain up to 700 billion barrels... 700 billion barrels of oil. But only about 1-2% of that is recoverable.

The oil in these places is so tightly trapped in sandstone that conventional vertical wells prove worthless at extracting it. But in the last 10 or 15 years, engineers have figured a few ways to get at it.

One way is horizontal drilling. Instead of just drilling a well straight into a deposit like a straw, this method starts vertically and then angles to approach from the side, running the length of the reservoir in order to maximize the well's exposure to the trapped oil.

Engineers have also discovered that if you create fissures in the rock by injecting a combination of water, sand and chemicals at extremely high pressure, oil will seep through the cracks and can be extracted through the horizontal pipes. This is method number two, and you know it as fracking.

Heavy Oil is an entirely different beast. The oil sands of Canada and Venezuela have dramatically altered predictions about how much usable oil we have in the world. Alberta's oil sands may contain between 1.7 and 2.5 trillion barrels of oil, of which maybe 15% is recoverable. That still amounts to about 75% of the petroleum reserves in North America. Also called 'tar sands' or 'bituminous sands', oil sands are a mixture of sand, water, clay and bitumen - a thick mixture of hydrocarbons found in crude petroleum. Bitumen is so thick that it basically is a semi-solid with the consistency of molasses. 

Scientists aren't sure how these enormous deposits came to be. Some think that they're remnants of crude oil reservoirs that were destroyed microbiologically, leaving the bitumen behind. Others think that underground pressure forced it up from shale deposits where hydrocarbons soaked into the sediments and sand on the surface. Either way, since bitumen makes up between 1 and 20% of these oil sands, conventional extraction methods just don't work. It would be like trying to drink up the world's absolutely thickest milkshake through a crazy skinny straw.

So instead, oil companies just attack it at the surface - a lot like how some minerals are mined. Some of the largest excavators and trucks you have ever seen in your life are used to scrape away top soil and dig out the underlying tar sands. The mixture is then steamed to extract the bituminous oil and piped to refineries.

But only 20% of the tar sands can be mined like this; the rest is too deep in the ground. To get at that stuff, oil companies often use a process called 'steam assisted gravity drainage'. It involves digging two horizontal wells - one near the bottom of the reservoir and the other a few meters above it. Steam is injected into the upper well to loosen up the bitumen, which then flows in the other well, where it can be drawn up.

Now you've probably noticed that whether we're talking about conventional or unconventional oil, finding it is usually pretty freaking complicated, and the harder it gets for us to find the oil, the more we're pushing the limits of what machines can do and what engineers can dream up, so its worth noting the extra effort and energy that's now required to extract the 'Black Gold' from the ground.

At some point, probably in your lifetime, the cost of extracting oil will get so high that it'll no longer be economically viable for either the producer or the consumer to use it. At least in the ways we currently use it, which is pretty wasteful and so everyone knows that its time to start exploring alternative energy sources that don't require squeezing oil out of sand.

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