Oil sands are deposits of sand, clay, water, and a dense, highly viscous form of petroleum known as bitumen. This bitumen is so thick that at room temperature, it has a consistency similar to cold molasses or peanut butter, which prevents it from flowing naturally like conventional crude oil. Specialized extraction methods are necessary to reduce the bitumen’s viscosity and separate it from the surrounding materials. The vast majority of the world’s accessible oil sands reserves are concentrated in the Athabasca, Cold Lake, and Peace River regions of Alberta, Canada.
Surface Mining and Hot Water Separation
Surface mining is used for oil sands deposits that lie relatively close to the surface, typically less than 75 meters deep, which accounts for about 20% of the total recoverable resource. The process begins with the physical removal of the overburden, which is the soil and rock covering the oil sands layer. This excavation is accomplished using massive equipment, including large hydraulic shovels and heavy-haul trucks.
Once exposed, the oil sands ore is transported to a primary crushing facility. The ore is broken down and mixed with hot water and steam to create a slurry. This mixture conditions the bitumen, allowing it to be pumped through hydrotransport pipelines to the extraction plant. The movement through the pipeline helps further separate the bitumen from the sand and clay particles.
At the extraction plant, the slurry enters large separation vessels for the hot water extraction process. Hot water, maintained around 80 to 85°C, causes the bitumen to separate from the sand grains. Air bubbles are injected into the mixture, attaching to the lighter bitumen droplets and causing them to float to the surface as a bitumen froth. This froth is skimmed off, while the heavier sand and clay particles settle to the bottom.
In-Situ Steam Injection Methods
For the roughly 80% of oil sands reserves located too deep for surface mining, operators use in-situ, or “in-place,” extraction methods. These techniques involve injecting heat underground to make the bitumen fluid enough to be pumped to the surface. This approach uses wells drilled from the surface, resulting in minimal land disturbance compared to mining.
The most widely used in-situ technique is Steam Assisted Gravity Drainage (SAGD). This method involves drilling a pair of horizontal wells deep into the oil sands formation, with one positioned a few meters above the other. High-pressure steam is continuously injected into the upper wellbore, creating a growing chamber of heat that significantly lowers the bitumen’s viscosity.
As the bitumen heats up, it becomes less viscous and flows down into the lower production well due to gravity. The heated bitumen and condensed steam are pumped to the surface for processing. SAGD is known for its high recovery rates, often exceeding 60% of the oil in place, making it the standard for deep deposits.
An alternative in-situ method is Cyclic Steam Stimulation (CSS), sometimes called the “huff and puff” method. CSS uses a single well that cycles through three distinct phases. Steam is injected into the reservoir to heat the bitumen. Next, the well is “soaked,” allowing the heat to disperse throughout the deposit. Finally, the heated and mobilized bitumen is produced through the same well.
Preparing the Bitumen for Market
Regardless of the recovery method, bitumen must be prepared before it can be transported or refined. Raw bitumen is too thick and viscous to flow efficiently through conventional pipelines, presenting a significant logistical challenge. The two primary ways to make bitumen transportable are dilution and upgrading.
Dilution involves blending the raw bitumen with lighter hydrocarbon liquids, called diluents. This mixture, known as “Dilbit,” lowers the overall viscosity and allows the product to meet pipeline specifications. The diluent is later separated from the bitumen at the destination refinery.
The other option is upgrading, which transforms the heavy bitumen into a lighter, less viscous product known as Synthetic Crude Oil (SCO). Upgrading involves complex processing, typically either coking or hydrocracking. Coking is a thermal process that breaks down large bitumen molecules by removing carbon, resulting in a lighter product and a solid petroleum coke by-product.
Hydrocracking upgrades the bitumen by adding hydrogen to the molecules, which improves the hydrogen-to-carbon ratio and creates a cleaner, higher-quality synthetic crude. Upgrading significantly improves the quality of the oil, making it easier for standard refineries to process into gasoline, diesel, and other petroleum products.