HOW IT WORKS
How is Heavy Oil Produced?

Recovery
Some heavy oil production can be accomplished via conventional methods, such as vertical wells, pumps, and pressure maintenance, but these methods are considered highly inefficient. Other technologies being used to recover heavy oil include, but are not limited to: cold heavy oil production with sand (CHOPS), vapor extraction (VAPEX), and thermal in situ methods. The main oil-related challenges involved in production are gravity and the viscosity of heavy oil.

The CHOPS method allows sand into the wellbore with the oil to improve well productivity. Wells that formerly produced only 20 barrels/day have been observed to produce more than 200 barrels/day, according to Canada's Centre for Energy, with free movement of sand into the wellbore. This technology was pioneered in Canada.

A non-thermal recovery method that involves injecting vaporized solvents into heavy oil, VAPEX creates a vapor-chamber that oil flows through due to gravity drainage. It has the potential to lower greenhouse gas emissions and significantly reduce water consumption, compared to other technologies currently in use, and can be used to recover bitumen from zones too thin for traditional thermal recovery.

Steam-assisted gravity drainage (SAGD) is a thermal in situ recovery method that involves drilling two horizontal wells, one above the other. Steam is continuously injected through the upper wellbore, softening bitumen so that it drains into the lower wellbore and is pumped to the surface. Pairs of parallel horizontal wells, one for steam and one for production, make it possible to recover bitumen continuously from oil sands.

Cyclic steam stimulation, also a thermal in situ recovery method, is a three-stage process involving several weeks of steam injection, followed by several weeks of "soaking," followed by a production phase where the oil is produced by the same wells in which the steam was injected. As production declines, the injection phase is restarted. The high-pressure steam not only makes the oil more mobile, but also creates cracks and channels through which the oil can flow to the wellbore.

Processing
Heavy oil and bitumen consist of large hydrocarbon molecules, which contain proportionately more carbon atoms than hydrogen atoms. Upgrading processes add hydrogen atoms and/or remove carbon atoms to convert bitumen into a product similar to conventional light crude oil.

Upgrading is usually a two-part process, as explained by Canada's Centre for Energy. In the first stage, bitumen is heated and hydrogen added under high pressure to break the large hydrocarbon molecules into simpler, smaller compounds. This process is known as "hydrocracking." Some upgraders also use a "coking" process to remove carbon from the bitumen to produce lighter hydrocarbons and coke (a carbon material that resembles finely ground asphalt). During the second stage, hydrogen is added to the hydrocarbon compounds to stabilize them and remove impurities such as sulfur. This process is called "hydrotreating."

Upgrading results in three main products: naphtha, kerosene, and gas oil (a fuel oil somewhat heavier than kerosene). These can be sold separately or blended to produce synthetic crude oil for sale to refineries.

Sally Cole Johnson is a freelance writer based in Windham, NH. She earned a B.A. in geology from the University of New Mexico and specializes in earth science and semiconductors.

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