Heavy oil is a form of unconventional oil that is thick and highly viscous, and therefore does not flow to production wells under normal reservoir conditions.
Heavy crude oil is any liquid petroleum with an API gravity of less than 22.3°.
readings are based on the American Petroleum Industry's method of determining the gravity of crude oil
A heavy crude is in the 15-25 °API range.
Anything below 15 °API would be considered an extra-heavy crude.
The presence of asphaltenes, chemically altered fragments of organic chemical compounds, in oil can greatly complicate the production process.
Subsequently, certain asphaltene elements require that the heavy oil also undergo a special refining process called deasphalting.
The chemical composition of asphaltenes can consist of various amounts of sulphur
, oxygen, hydrogen, nitrogen, carbon, and the heavy metals nickel and vanadium and are widely recognized as soluble.
The resources of heavy oil in the world are more than twice those of conventional light crude oil.
The world’s two largest oil deposits are the heavy and extra heavy oil deposits of Venezuela and Canada.