Heavy crude oil

What is Heavy Crude Oil?

Heavy crude oil is a type of oil that is very thick and does not flow easily from wells. It is called "heavy" because it is denser than lighter types of oil, like light crude oil.

How is Heavy Crude Oil Measured?

One way scientists measure how heavy oil is comes from its API gravity, which should be less than 20° to be considered heavy crude.

Special Properties of Heavy Crude Oil

Heavy crude oil has some special properties. It is more viscous, meaning it is thicker, and has a higher molecular weight compared to lighter oils. It is also made of heavier hydrocarbon molecules.

In 2010, the World Energy Council said that extra heavy oil is even thicker, with a gravity less than 10° and a viscosity more than 10,000 centipoises. When we cannot measure viscosity easily, they say oil is extra heavy if its API gravity is less than 4°.

Heavy Crude Oil in the Environment

Heavy oils behave differently in the environment. They are dense and do not mix with water. If they spill into water, they sink to the bottom rather than staying on the surface. This makes cleaning up such spills quite challenging.

Reserves

Big amounts of heavy oil are found in Canada and Venezuela. In 2001, the U.S. Energy Information Administration said the largest heavy oil reserves were north of the Orinoco River in Venezuela’s Orinoco Belt. At that time, Venezuela allowed partnerships to work on these oil resources. It was estimated that there were 270 billion barrels of oil that could be collected there. The Orinoco Belt is sometimes called oil sands, but it is actually heavy or extra-heavy oil because it does not flow easily. More than thirty countries have these kinds of oil reserves.

Extraction

Heavy oil is being found and used more often in many countries. Canada and Venezuela were the top places to get it in 2008. There are many ways to get heavy oil out of the ground. Some ways are using cold oil with sand, steam-assisted gravity drainage, steam injection, vapor extraction, toe-to-heel air injection, and even open-pit mining in places with a lot of sand and oil.

Working with heavy crude oil is harder than with light crude oil. To help it move through pipelines, a special mix called diluent is added. This mixed oil, called dilbit, makes it easier to move the very thick oil.

Heavy crude oil can affect the environment more than lighter oil. It often needs more energy to get it out of the ground and to make it ready to use. This can lead to more carbon dioxide going into the air. Scientists are searching for better ways to lessen these effects. Some reports say that getting oil from places like Canadian oil sands can create more emissions during the whole time the product is used, compared to regular oil. Heavy crude oil is also important for making road asphalt.

Economics

Heavy crude oil is important for oil development. There is more heavy oil in the world than light oil. In October 2009, the United States Geological Survey updated the Orinoco deposits to 513 billion barrels (8.16×10¹⁰ m³), making it one of the largest oil deposits. However, it can be hard to get the oil out. Only a small amount of the oil can usually be collected.

Heavy oil can be more expensive to process and may have more sulfur, so it is often sold for less money than lighter oil. It is also harder to produce because it is thick and dense. But large amounts of heavy oil have been found in places like Canada, Venezuela, and California. Even though these oil fields are not very deep, special methods are needed to get the oil out.

Properties

Heavy oil is found in shallow, young rock layers from the Pleistocene, Pliocene, and Miocene periods. These layers are younger than 25 million years old. Sometimes heavy oil is also in older rock layers from the Cretaceous, Mississippian, and Devonian periods.

Heavy oil has a thick, slow-moving texture. This is because it has more complex compounds and fewer simple ones. It also has many compounds with over 60 carbon atoms, which makes it boil at higher temperatures. For example, the Orinoco extra-heavy crude oil is very thick, like molasses.

Heavy crude oils are grouped in two ways: those with a lot of sulfur, found in North America like Canada and the United States, and South America like Venezuela; and those with less sulfur, found in Western Africa, Central Africa, and East Africa.

Related substances

Heavy crude oil is closely related to natural bitumen from oil sands. Bitumen from oil sands is called extra heavy oil because it is very thick and dense. Natural bitumen is even thicker and heavier than heavy oil, and it does not flow easily. Both heavy oil and bitumen are different from lighter oils because they are thick and dense. Most heavy oil is found at the edges of underground rock layers and is thought to come from lighter oil that changed over time. Bitumen is often much thicker than cold molasses and does not flow easily under normal conditions.