In-situ extraction methods are used to recover bitumen that lies too deep beneath the surface for mining (greater than 75 metres underground). Currently, 80% of oil sands reserves are accessible via in-situ techniques.
Steam Assisted Gravity Drainage (SAGD) is currently the most widely used in-situ recovery method. This method requires the drilling of two horizontal wells, one slightly higher than the other, through the oil sands deposit. Steam is injected continuously into the top well and, as the temperature rises in what is termed the “steam chamber”, the bitumen becomes more fluid and flows to the lower well. The bitumen is then pumped to the surface.
Open Pit Mining
Open-pit mining is similar to traditional mineral mining operations and largely employed where oil sands reserves are closer to the surface (less than 75 metres underground). Currently, 20% of oil sands reserves are accessible via mining techniques.
Large shovels scoop the oil sand into trucks which then move it to crushers where the large clumps of earth are processed. Once the oil sand is crushed, hot water is added so it can be pumped to the extraction plant. At the extraction plant more hot water is added to this mixture of sand, clay, bitumen, and water in a large separation vessel where settling time is provided to allow the various components to separate. During separation, bitumen froth rises to the surface, where it is removed, diluted, and refined further.
Bitumen recovered from open pit mines or from in situ extraction is a very thick, viscous substance that has to be upgraded or diluted in order to be pipelined and used as feedstock in refineries.
The purpose of upgrading is to transform bitumen into synthetic crude oil (SCO) which can be refined and marketed as consumer products such as diesel and gasoline. Upgrading processes involve either adding hydrogen or removing carbon from the bitumen to create SCO.
Although the overall upgrading process flow diagram varies from company to company, generally the process is broken down into two broad types of upgrading, namely primary and secondary upgrading. Primary upgrading breaks down the heavy molecules of bitumen into lighter and less viscous molecules. Secondary upgrading is meant to further purify and distill the bitumen obtained from primary upgrading to remove unnecessary impurities such as nitrogen, sulphur, and trace metals so that it could be used as feedstock for oil refineries.
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