Updated October 2009

Mining Methods
Oil sands development is carried out through either conventional or non-conventional methods. Conventional involves removing the sand which contains the bitumen using open pit mining methods. Non-conventional is carried out by processing the sand while still in place using in situ methods.

Conventional mining involves stripping the overburden to gain access to the oil sands formation which is then removed using truck and shovel methods. The bitumen is separated from the sands by adding warm water and agitating the mixture.

In situ mining of the bitumen involves removal of the bitumen from the sand while it is still in place; this is most commonly achieved through the addition of heat which causes the bitumen to flow and collect in pipes for pumping to the surface. Some projects employ a cyclic steam stimulation (CSS) method while others use steam assisted gravity drainage (SAGD).

Technologies being developed and put into practice include the vapour recovery extraction method (VAPEX) which utilizes solvents to separate the bitumen from the sand. Another method is the primary or cold production method which can be used in reservoirs where the bitumen will flow to wells without the introduction of heat.

Roughly two thirds of production is achieved through conventional mining methods with the remaining one third recovered using in situ methods. This ratio will reverse over time as it is estimated that approximately 80% of the oil sands in State Alberta are too deep to be open pit mined.

For a list of oil sands projects (as of September 2009) and the extraction methods they use, please see this update on the industry by the Alberta Government.

Bitumen Extraction
Removing the bitumen from the sand is generally a four-step process.

1. The sand is mixed with water, large clumps are broken down and coarse material is removed.
2. The resultant slurry is fed into a primary separation vessel (PSV) where the sand settles to the bottom. A mixture of sand, water and bitumen (called middlings) remains suspended in the middle and an impure bitumen froth floats to the top and is removed for further processing.
3. The sand at the bottom of the tank is pumped into tailings ponds and the middlings go through a secondary separation process where an additional 2-4% of the bitumen is removed as froth.
4. The froth is then diluted with naphtha to decrease its viscosity. Water and solids remaining in the bitumen froth are removed using centrifuges and settling units and the bitumen is sent to the upgrader to be converted to synthetic crude oil.

The Oil Sands Discovery Center has produced a series of fact sheets including one on the extraction process.

Waste Disposal

Water used for extraction at oil sands mines ends up in tailings – a slurry of bitumen, water, sand, silt and fine clay particles – that is pumped to tailings ponds. While commonly referred to as ponds, these enormous bodies of water and the dykes that contain them are some of the largest human-made structures in the world. Collectively, they cover an area of land greater than 50 square kilometers.

Tailings ponds are constructed with materials created during the mining and extraction process. The containment dyke is first constructed using the overburden, the surface rock and soil that must be removed to access the oil sand resource below. Once oil sand processing begins, the coarse tailings sand is used to build dykes around the periphery. The fine tailings are then contained in the centre of the pond. As the tailings age they consolidate, releasing a layer of clear water that is recycled back into the extraction process. (Source: Alberta Environment)

It takes roughly two tonnes of sand to produce one barrel of oil. Oil sand tailings management therefore is a major consideration and is explored in the publication Oil Sands Technology Roadmap produced by the Alberta Chamber of Resources.

The University of Alberta has an Oil Sands Tailings Research Facility (OSTRF) that was created to facilitate innovative research and development of the next generation of environmentally superior tailings for Alberta's oil sands industry. The infrastructure consists of three independent modules for delivery/production, treatment and deposition of tailings. For more information see their website as well as this paper by Beier and Sego.

In February 2009 the Energy Resources Conservation Board of Alberta (ERCB) came up with certain performance criteria for oil sands tailings. Take a look at this document for details.

Upgrading
When the bitumen has been removed from the sand the next step is to upgrade it into synthetic crude oil. Some operations do not carry out the upgrading onsite, the Athabasca Oil Sands Project for instance pipes the bitumen it processes from the Muskeg River mine 435 km south through a pipeline to the Scotford Upgrader for further processing. Other companies choose to sell several different types of oil products according to demand from the market.

Before any upgrading can take place the naphtha left over from froth treatment must be removed through a process of distillation. After the naphtha has been removed there are 4 main steps involved in upgrading bitumen into synthetic crude oil.

1. Thermal conversion or coking uses heat to break down or ‘crack’ the long hydrocarbon molecules that form bitumen. This process concentrates extra carbon into a byproduct called coke while leaving behind lighter products such as gas oils, and kerosene distillates. There are 2 types of coking in bitumen upgrading; ‘delayed’ which uses a dual chambered coking drum and ‘fluid’ which uses a single chambered coking drum. Some of the coke is used along with natural gas as fuel for furnaces which produce the heat required for the coking process. Very little of the coke is used for heating and the excess is stockpiled for possible future use or sale.
2. Further refinement is achieved through a catalytic conversion which breaks oil molecules down into even smaller, more refineable hydrocarbons. High pressure hydrogen is sometimes added during this process to enable the production of lighter, hydrogen-rich molecules.
3. After coking and catalytic conversion the semi-refined bitumen is distilled, a process which separates it into its component parts. This process is carried out in a fractionating tower where the temperature varies with the hottest temps on the bottom and the coolest on the top. The lightest hydrocarbons travel as vapour to the top of the tower and heavier, denser ones collect in the bottom.
4. The gas oils, kerosene and naptha which was separated during the distillation process are then subjected to high pressure, high temperature hydrogen , a process called hydrotreating. This process stabilizes the hydrocarbon by adding hydrogen to the unsaturated molecules and removes impurities such as nitrogen and sulphur.

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