It’s termed petroleum; crude oil, more technically correctly referred to as this rather complex hydrocarbon mixture. Petroleum is derived mainly from the organic compound of ancient flora and marine life that has passed through heat and pressure for millions of years. While the physical properties of petroleum vary significantly with each source, viscosity is considered one of the main physical properties that varies. Yet, can petroleum be viscous? Which factors influence the viscosity of petroleum?

What is Viscosity?

Viscosity is a fluid’s resistance to flow; it measures how “thick” or “sticky” a liquid can be. Consider water. For example, water has a low viscosity, while honey or molasses has a high viscosity. This property is essential in transporting, refining, and processing petroleum.

In petroleum, viscosity is crucial in determining how effortlessly it can traverse pipelines, be extracted from oil wells, or undergo processing in refineries. The greater the viscosity, the more energy and pressure are required to propel it forward. In contrast, a lower viscosity signifies that the oil glides more easily.

Factors Influencing Petroleum’s Viscosity

The viscosity of petroleum is not uniform; it can be highly dependent on many factors:

1. Composition is an essential aspect in determining viscosity, primarily with petroleum. Crude oil is a complex mixture of hydrocarbons of varied molecular sizes and structures. Lighter hydrocarbons like methane or ethane have relatively low viscosity, whereas heavy compounds like bitumen or asphaltenes have a very high viscosity. The greater the percentage of heavy hydrocarbons, the greater the viscosity of the oil and its resistance to flow.
2. Temperature: Petroleum’s viscosity decreases with an increase in temperature; if oil is thick, extraction and transportation may prove quite tricky at lower temperatures, and in warmer environments, the oil flows exceptionally well. Oils found in northern parts, such as Canada’s oil sands, are much thicker and even more viscous, in contrast to those extracted from warmed water in the Gulf.
3. Increased pressure can lower petroleum’s viscosity. The oil must endure high pressure at reservoir depths that significantly decrease viscosity. Once brought out and extracted to the surface, however, pressure lowers, and oil increases its viscosity. This is why some oils, for instance, in deep-sea reservoirs, are more complex to pump without special equipment.
4. In some instances, wax and paraffin can make up a large percentage of crude oil; they can freeze at low temperatures. This increases the oil’s viscosity, making it more difficult to transport. For example, some varieties of crude oil from the North Sea or Venezuela are notorious for their high wax content and, if not treated appropriately, can cause pipeline blockages.
5. API gravity is a method of classifying petroleum, showing whether the oil is heavier or lighter than water. Oils with low API gravity, often heavier oils, have a higher viscosity. On the other hand, oils with high API gravity are called lighter oils, and they have lower viscosity. Heavy oils, including bitumen and extra-heavy crude, are much more viscous than light sweet crude oils.

Can Petroleum Be Viscous?

Yes—petroleum can be viscous, and in many cases, it is. Heavy crude oils include bitumen, extra-heavy crude, or tar sands. Such varieties of petroleum are very thick and sticky and pose problems in extraction and transportation. The oil sands of Alberta, Canada, are one quintessential example of petroleum with an extremely high viscosity. These oils are so viscous that they often have to be heated or thinned with lighter hydrocarbons, such as natural gas liquids, to reduce viscosity and flow more freely through pipelines.

Viscosity Problems in Oil Extraction

Viscous petroleum is highly problematic in extraction and transportation. The primary problem occurs in the pumping process. Traditional oil extraction relies on pressure difference to force the oil to the surface. However, if the oil is viscous and sticky, it becomes difficult to pump; additional equipment or energy is needed. Steam injection or in-situ heating is usually used to make heavy oil less viscous so that it is easier to pump.

For instance, the SAGD method is widely applied in Alberta’s oil sands. In this method, steam is injected into the grounds to warm the oil and reduce its viscosity so that it can pass to the surface. Such methods require vast amounts of energy and may be expensive.

Another problem associated with viscous petroleum is transferring the product. While crude oil is primarily transferred through pipelines, dense oils can clog or reduce pipe flow. The problem can be addressed by heating the pipes, or special additives such as diluents that dilute the oil to minimize viscosity can be mixed in the crude oil. Introducing such diluents into crude oil ensures unobstructed oil flow in pipes; however, it is expensive.

Refining Viscous Petroleum

Refining viscous petroleum has its specific problems. The higher viscosity oil is hard to process because it cannot pass through smooth stages of oil processing via conventional refining methods. Mostly, these oils need preheating or dilution before feeding into the refinery.

Conclusion

It can be viscous when the petroleum contains heavy hydrocarbons like bitumen or has a high wax content. Viscosity is essential in all oil extraction, transportation, and refining processes. With the increased demand for heavy crude oils, such as oil sands, technological innovations are continuously improving to overcome the problems with high-viscosity petroleum. Whether through steam injection, pipeline heating, or incorporating diluents, the oil industry is finding ways to manage and overcome the thick viscosity of crude. While viscous crude creates problems, it can also meet a large portion of the world’s energy needs if the proper technology and processes are implemented.