What are oilsands and heavy oil?
Heavy oil and bitumen (the primary hydrocarbon component of oilsands) are types of crude oil, a naturally occurring petroleum. Petroleum is the general term for solid, liquid or gaseous hydrocarbons. Hydrocarbons are a class of organic compounds consisting only of carbon and hydrogen and which are the basis of oil, natural gas and coal. Technically, crude oil consists of pentanes (hydrocarbon chains consisting of five carbon atoms and 12 hydrogen atoms) and heavier hydrocarbons (hydrocarbon chains longer than five carbon atoms in the formula). It may also contain other substances such as water, natural gas, sulphur and other minerals. Conventional crude oil is oil that flows naturally or that can be pumped without being heated or diluted. Crude oil is commonly classified as light, medium, heavy or extra heavy, referring to its gravity as measured on the American Petroleum Institute (API) Scale. The API gravity is measured in degrees and is calculated using the formula API Gravity = (141.5/S.G.) - 131.5, as illustrated in the table. Industry defines light crude oil as having an API gravity higher than 31.1° (lower than 870 kilograms/cubic metre), medium oil as having an API gravity between 31.1° and 22.3° (870 kilograms/cubic metre to 920 kilograms/cubic metre), heavy oil as having an API gravity between 22.3° and 10° (920 kilograms/cubic metre to 1,000 kilograms/cubic metre), and extra heavy oil (bitumen) as having an API gravity of less than 10° (higher than 1,000 kilograms/cubic metre). The Canadian government has only two classifications, light oil with a specific gravity of less than 900 kilograms/cubic metre (greater than 25.7° API) and heavy oil with a specific gravity of greater than 900 kilograms/cubic metre (less than 25.7° API). A less rigorous definition of heavy oil is oil that is “not recoverable in its natural state through a well by ordinary production methods.” However, some heavy oil less than 22.3° API does flow very slowly but most requires heat or dilution to flow into a well or through a pipeline. Heavy oil from the Lloydminster area of Alberta and Saskatchewan has API gravities ranging from 9° to 18°. Heavy oil makes up about 15 per cent of the world‟s remaining oil reserves. It usually contains impurities such as sulphur, heavy metals, waxes and carbon residue that must be removed before it is refined. The definition is more appropriate for bitumen, oil that “does not flow, or cannot be pumped without being heated or diluted.” The bitumen mined from the oilsands deposits in the Athabasca area of Alberta, Canada has an API gravity of around 8°, but is upgraded to an API gravity of 31° to 33°. This upgraded oil is known as synthetic oil. Oilsands are mixtures of sand, water, clay and crude bitumen. Each oilsand grain has three layers: an „envelope‟ of water surrounding a grain of sand, and a film of bitumen surrounding the water. Composition of oilsands View larger
The difference between heavy and light oil View larger
How are oilsands and heavy oil used?
Ultimately, heavy oil and bitumen are used to make the same petroleum products as conventional forms of crude oil; however, more processing is required. In 2002, heavy oil, synthetic oil and crude bitumen accounted for
almost 60 per cent of total Canadian crude oil production. Oil fuels more than 33 per cent of Canada‟s total energy needs. Approximately 75 per cent of the oil produced in Canada is refined into transportation fuels - gasoline and diesel for cars and trucks, kerosene for jet aircraft and fuel oil for ships. Other energy uses include domestic and industrial heating, fuels for industrial purposes and generating electricity.
How are oilsands and heavy oil formed?
Like other forms of petroleum, the formation of heavy oil and bitumen began with plants using solar energy to convert carbon dioxide and water into oxygen and carbohydrates through a process known as photosynthesis. When the plants, primarily algae, and small organisms (plankton) that fed on them died, the sediments containing the remains became buried at the bottom of a vast inland sea. As the depth of burial increased, heat and pressure transformed the carbohydrates into hydrocarbons. Coal is a solid hydrocarbon derived from land plants. Oil is a liquid hydrocarbon derived primarily from simple marine plants and animals, and natural gas is a gaseous hydrocarbon derived from either terrestrial or marine materials at a higher temperature and pressure than coal or oil. Oil formation takes place in source rocks, usually very fine-grained rocks known as black shales. Once the oil is formed, continued pressure from overlying rock strata forces the oil to migrate through permeable rock layers until it is trapped in reservoirs of porous sedimentary rock such as sandstone or limestone, or until it escapes at the surface. The liquid hydrocarbons that comprise the oil include a range of light to heavy compounds. The molecules of light compounds contain a few atoms of carbon surrounded by hydrogen atoms. The molecules of heavy compounds consist of many more carbon atoms and relatively fewer hydrogen atoms. Wax, grease, tar and asphalt are examples of heavy compounds. As the eons passed, the oil-bearing sediments were covered by more than a kilometre of sedimentary rock. Then, about 50 million years ago, vast amounts of the liquid hydrocarbons migrated more than 100 kilometres eastward and upward until they reached and saturated large areas of sandstone at, and just below, the surface of what is now northern Alberta. Micro-organisms present in the sandstone slowly consumed the hydrocarbons, beginning with the lightest. The heavy oil and bitumen now being produced from the area are the remnants of that migration. They are still the world‟s largest known hydrocarbon resource deposit, but scientists believe the amount of crude oil digested by the micro-organisms was two or three times what remains.
How are oilsands and heavy oil found?
Shallow oilsands are identified by thick, viscous oil seeping from the ground. In fact, oil from seeps along the Athabasca River has been used by aboriginal peoples for many generations to caulk the seams of their canoes, and may have been used to dress wounds and waterproof garments. Deeper deposits are often identified using Automated 2-D Electrical Imaging, a geophysical technique that plots electrical conductivity variations in the earth. Geoelectrical sections can generally be interpreted as geological cross sections. Because oilsands are highly resistive, the technique can be costeffectively used for the exploration and delineation of these resources
Thermal in-situ recovery For both oilsands and heavy oil, steam is often used to facilitate production by softening the bitumen, diluting and separating it from sand grains, and enlarging or creating channels and cracks through which the diluted oil can flow.
Existing in-situ technology uses natural gas-fired boilers to generate steam. The process requires a lot of water-up to three cubic metres for each cubic metre of bitumen produced-but more than 80 percent of the water is recycled. Current in-situ production technologies recover between 25 and 60+ per cent of the bitumen in the reservoir-a somewhat higher recovery rate than most conventional light crude oil wells. The two most successful methods are cyclic steam stimulation and steam-assisted gravity drainage (SAGD). Cyclic steam stimulation: 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, it creates cracks and channels through which the oil will flow to the wellbore. Steam saturates the oilsands formation, softening and diluting the bitumen so it can flow to the well during the production phase. Bitumen produced from Shell Canada’s Peace River complex is blended with locally supplied condensates for pipeline injection. The bitumen is marketed to refiners with heavy oil refining capabilities and is preferred feedstock for producing asphalt.
Peace River complex, northwestern Alberta
Source of image: Shell Canada
View larger A variation of cyclic steam stimulation was developed by Shell Canada for the Peace River oilsands plant. The “soak radial” technique utilizes a vertical well with four horizontal arms that extend spoke-like into the reservoir. Steam is injected for two months, followed by six to 18 months of reverse action during which oil is pumped to the surface through the same horizontal arms.
Horizontal wells, Peace River complex
Source of image: Shell Canada