What is In Situ?
In Situ comes from the latin term meaning “in position” or “on site” and refers to the oil sands technologies used to recover bitumen that lies too deep beneath the surface to be mined (more than 75 meters deep) and too viscous to flow on its own. In situ production is required for approximately 80% of the bitumen found in the oil sands. The most commonly used technology for in-situ production is Steam Assisted Gravity Drainage (SAGD). Therfore, more emphasis in the article is placed on this technique. However, there are 3 other techniques also in use:
- Cyclic Steam Simulation (CSS) – uses a single vertical well and the injection of steam to recover bitumen.
- Toe to Heel Air Injection (THAI) – involves igniting air and injecting it into a vertical well to melt bitumen and recover it.
- Vapour Extraction Process (VAPEX) – uses solvents to increase the viscosity of oil sands for recovery.
SAGD was invented in 1978. SAGD works by drilling two horizontal wells beneath the surface, parallel to each other, about four to six meters apart. The top well is injected with steam that heats the surrounding bitumen, reducing its viscosity. This is the Steam Assisted (SA) part of the name. The less-viscous bitumen then drains into the bottom well with the help of gravity and is pumped to the surface. This is the Gravity Drainage (GD) part of the name. The produced bitumen is mixed with hydrocarbons to further reduce its viscosity and is then stored in storage tanks for transportation and further processing1.
SAGD has several advantages over oil sands mining. SAGD production has less land disturbance and does not result in the creation of tailings ponds. However, SAGD requires large amounts of thermal energy to produce steam. Currently the vast majority of this energy is provided by natural gas, a non-renewable and hydrocarbon fuel source, making greenhouse gas emissions a key concern2.
In addition, water use is another important concern. The SAGD process requires a significant amount of water, although 80 to 95 percent of the water used is recycled back into the process. Some SAGD operations also use saline water that is determined to be unsuitable for drinking or irrigation purposes in order to minimize the use of fresh water3.
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