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

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 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, which is the same amount as the regular oil in Saudi Arabia. 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

Production of heavy oil is becoming more common in many countries, with Canada and Venezuela leading in 2008. There are several ways to get heavy oil out of the ground, such as using cold oil with sand, steam-assisted gravity drainage, steam injection, vapor extraction, toe-to-heel air injection, and even open-pit mining for very sandy and oil-rich places.

Working with heavy crude oil is trickier than with light crude oil. To help it flow in pipelines, a special mix called diluent is added at regular points. This mixed oil, known as dilbit, makes it easier to transport very thick oil.

Heavy crude oil can have a bigger impact on the environment than lighter oil. It often needs more energy to extract and refine, which can lead to more carbon dioxide emissions. Researchers are looking for better ways to reduce these effects. Some reports show that getting oil from places like Canadian oil sands can create more emissions over the whole life of the product compared to regular oil. However, heavy crude is also useful for making road asphalt.

Economics

Heavy crude oil is interesting for the economics of 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 5-30% 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, which are younger than 25 million years old. Sometimes it is also in older rock layers from the Cretaceous, Mississippian, and Devonian periods.

Heavy oil contains special kinds of materials and has a thick, slow-moving texture. This is because it has more of certain complex compounds and fewer simple ones. It also has a lot of compounds with over 60 carbon atoms, making it boil at higher temperatures. For example, the Orinoco extra-heavy crude oil is very thick, like molasses, and can be up to 100,000 times thicker than water in some places.

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 considered extra heavy oil because it is very thick and dense. Natural bitumen is even thicker and heavier than heavy oil, with a very high resistance to flow. Both heavy oil and bitumen are different from lighter oils because they are thick, dense, and contain certain chemicals. 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.