Heavy Crude Oil - Chemical Properties

Chemical Properties

Heavy oil is asphaltic and contains asphaltenes and resins. It is "heavy" (dense and viscous) due to the high ratio of aromatics and naphthenes to paraffins (linear alkanes) and high amounts of NSO's (nitrogen, sulfur, oxygen and heavy metals). Heavy oil has a higher percentage of compounds with over 60 carbon atoms and hence a high boiling point and molecular weight. For example, the viscosity of Venezuela's Orinoco extra-heavy crude oil lies in the range 1000–5000 cP (1–5 Pa·s), while Canadian extra-heavy crude has a viscosity in the range 5000–10,000 cP (5–10 Pa·s), about the same as molasses, and higher (up to 100,000 cP or 100 Pa·s for the most viscous commercially exploitable deposits). A definition from the Chevron Phillips Chemical company is as follows:

The "heaviness" of heavy oil is primarily the result of a relatively high proportion of a mixed bag of complex, high molecular weight, non-paraffinic compounds and a low proportion of volatile, low molecular weight compounds. Heavy oils typically contain very little paraffin and may or may not contain high levels of asphaltenes.

There are two main types of heavy crude oil:

1. Those that have over 1% sulfur (high sulfur crude oils), with aromatics and asphaltenes, and these are mostly found in North America (Canada (Alberta, Saskatchewan), United States (California), Mexico), South America (Venezuela, Colombia and Ecuador) and the Middle East (Kuwait, Saudi Arabia).
2. Those that have less than 1% sulfur (low sulfur crude oils), with aromatics, naphthenes and resins, and these are mostly found in Western Africa (Chad), Central Africa (Angola) and East Africa (Madagascar).