Heavy oil is a naturally occurring petroleum that differs from conventional crude oil. It cannot easily flow from underground reservoirs under normal conditions, requiring specialized approaches for its extraction and subsequent processing, setting it apart in the global energy landscape. Its unique characteristics necessitate advanced technologies to harness its potential.
Defining Heavy Oil
Heavy oil is characterized by its distinct physical and chemical properties. It has a low API (American Petroleum Institute) gravity, a measure of how light or heavy a petroleum liquid is compared to water. Heavy crude oil typically has an API gravity below 22.3 degrees, indicating a higher density than conventional crude oils.
It also exhibits high viscosity, making it thick and resistant to flow, often resembling molasses at room temperature. Its chemical composition includes a higher proportion of complex, large molecular weight compounds, such as asphaltenes and resins. Heavy oil tends to have elevated levels of impurities, including sulfur and heavy metals. These properties make it more challenging to extract, transport, and refine compared to lighter crude oils.
Global Reserves of Heavy Oil
Heavy oil is found in various regions across the globe. Two of the largest accumulations are located in the Western Hemisphere. The Orinoco Oil Belt in Venezuela holds vast deposits of extra-heavy oil, estimated to contain hundreds of billions of technically recoverable barrels. This region alone accounts for a substantial portion of the world’s extra-heavy oil reserves.
Another major resource is the Athabasca oil sands in Alberta, Canada, which contain substantial reserves of bitumen, a more viscous form of heavy oil. While these two regions are dominant, heavy oil reserves are also present in over 30 countries, including parts of the United States, Mexico, Russia, and China.
Extraction and Processing Challenges
Extracting heavy oil presents technical difficulties due to its high viscosity, which prevents it from flowing easily through conventional wells. Specialized methods are necessary to reduce its thickness and enable production. Thermal enhanced oil recovery (EOR) techniques are commonly employed, involving the injection of heat into the reservoir.
One prominent thermal method is Steam-Assisted Gravity Drainage (SAGD), where two horizontal wells are drilled. High-pressure steam is continuously injected into the upper well, heating the heavy oil and reducing its viscosity, allowing it to drain by gravity into the lower production well. Another technique is Cyclic Steam Stimulation (CSS), also known as “huff and puff,” involves injecting steam into a single well, allowing it to soak, then producing the oil from the same well. These methods make the oil more mobile, enabling its recovery.
Once extracted, heavy oil requires extensive processing, known as “upgrading,” before it can be refined. Its high density and impurity content make it unsuitable for direct refining. Upgrading processes reduce the oil’s molecular weight, density, and viscosity, while also removing contaminants like sulfur and metals. Two primary approaches for upgrading include carbon rejection and hydrogen addition.
Carbon rejection processes, such as coking, thermally break down large hydrocarbon molecules, yielding lighter products and a solid carbon byproduct called petroleum coke. Hydrocracking, a hydrogen addition process, involves breaking down heavy molecules in the presence of hydrogen and a catalyst to produce lighter liquid fuels. These upgrading steps are energy-intensive and add to the overall cost and complexity of heavy oil production.
Uses of Heavy Oil
After undergoing extraction and upgrading, heavy oil is transformed into a range of petroleum products. One of its primary uses is in the production of asphalt, a thick, sticky substance widely used in road construction and roofing materials. Its dense and viscous nature makes it a suitable feedstock for creating this durable binding agent.
Heavy oil is also commonly used as fuel oil, particularly for industrial boilers, furnaces, and marine vessels. This type of fuel, often referred to as bunker fuel, powers large ships and is a key energy source for various industrial operations.
Upgraded heavy oil serves as a feedstock for the petrochemical industry. Through various chemical processes, it can be converted into components used to manufacture plastics, chemicals, and synthetic rubbers. While heavy oil can be upgraded to produce lighter products like gasoline and diesel, the intensive processing required means its main applications frequently lean towards heavier products.