Heavy crude oil (or extra heavy crude oil) is highly viscous oil that cannot easily flow from production wells under normal reservoir conditions. [1]
It is referred to as "heavy" because its density or specific gravity is higher than that of light crude oil. Heavy crude oil has been defined as any liquid petroleum with an API gravity less than 20°. [2] Physical properties that differ between heavy crude oils and lighter grades include higher viscosity and specific gravity, as well as higher molecular weight hydrocarbon composition. In 2010, the World Energy Council(WEC) defined extra heavy oil as crude oil having a gravity of less than 10° and a reservoir viscosity of more than 10,000 centipoises. [3] When reservoir viscosity measurements are not available, extra-heavy oil is considered by the WEC to have a lower limit of 4° API. [4] In other words, oil with a density greater than 1000 kg/m3 (or a specific gravity greater than 1) and a reservoir viscosity of more than 10,000 centipoises. [3] [5] Heavy oils and asphalt are dense nonaqueous phase liquids (DNAPLs). They have a low solubility and a viscosity greater than, and density higher than, water. [6] Large spills of DNAPL will quickly penetrate the full depth of the aquifer and accumulate at the bottom. [7]
Heavy crude oil is closely related to natural bitumen from oil sands. Petroleum geologists categorize bitumen from oil sands as 'extra-heavy oil' due to its density of less than 10° API. [8] Bitumen is the heaviest, thickest form of petroleum. [9] According to the U.S. Geological Survey, bitumen is further distinguished as extra-heavy oil with a higher viscosity (i.e., resistance to flow): "Natural bitumen, also called tar sands or oil sands, shares the attributes of heavy oil but is yet more dense and viscous. Natural bitumen is oil having a viscosity greater than 10,000 cP." [8] "Natural bitumen (often called tar sands or oil sands) and heavy oil differ from light oils by their high viscosity (resistance to flow) at reservoir temperatures, high density (low API gravity), and significant contents of nitrogen, oxygen, and sulfur compounds and heavy-metal contaminants. They resemble the residuum from the refining of light oil. Most heavy oil is found at the margins of geologic basins and is thought to be the residue of formerly light oil that has lost its light-molecular-weight components through degradation by bacteria, water-washing, and evaporation. Conventional heavy oil and bitumens differ in the degree by which they have been degraded from the original crude oil by bacteria and erosion. ( Meyer & Atanasi 2003 , p. 1) Often, bitumen is more viscous than cold molasses and does not flow at ambient conditions. [9]
According to the World Resources Institute, concentrations of remarkable quantities of heavy oil and oil sands are found in Canada and Venezuela. [2] [10] The U.S. Energy Information Administration (EIA) reported in 2001 that the largest reserves of heavy crude oil in the world were located north of the Orinoco river, in the 270-mile long by 40-mile wide Orinoco Belt, in eastern Venezuela. At that time Venezuela began authorizing "joint ventures to upgrade the extra-heavy crude resources." [11] Petroleos de Venezuela, S.A. (PDVSA) at that time estimated that there were 270 billion barrels of recoverable reserves in the area, [11] the same amount as the conventional oil reserves of Saudi Arabia. [12] The Orinoco Belt in Venezuela is sometimes described as oil sands, but these deposits are non-bituminous, falling instead into the category of heavy or extra-heavy oil due to their lower viscosity. [13] Natural bitumen and extra-heavy oil differ in the degree by which they have been degraded from the original conventional oils by bacteria. Thirty or more countries are known to have reserves.
Production, transportation, and refining of heavy crude oil present special challenges compared to light crude oil. Generally, a diluent is added at regular distances in a pipeline carrying heavy crude to facilitate its flow. Dilbit (diluted bitumen) is a means of transporting highly viscous hydrocarbons. Per the Alberta Oil Sands Bitumen Valuation Methodology, "Dilbit Blends" means "Blends made from heavy crudes and/or bitumens and a diluent usually condensate, for the purpose of meeting pipeline viscosity and density specifications, where the density of the diluent included in the blend is less than 800 kg/m3." [14] [15]
Heavy crude oils provide an interesting situation for the economics of petroleum development. The resources of heavy oil in the world are more than twice those of conventional light crude oil. In October 2009, the United States Geological Survey updated the Orinoco deposits (Venezuela) recoverable value to 513 billion barrels (8.16×1010 m3), [16] making this area one of the world's largest recoverable oil deposits. However, recovery rates for heavy oil are often limited from 5-30% of oil in place. The chemical makeup is often the defining variable in recovery rates. New technology utilized for the recovery of heavy oil is constantly increasing recovery rates. [17]
On one hand, due to increased refining costs and high sulfur content for some sources, heavy crudes are often priced at a discount to lighter ones. The increased viscosity and density also makes production more difficult (see reservoir engineering). On the other hand, large quantities of heavy crudes have been discovered in the Americas, including Canada, Venezuela and California. The relatively shallow depth of heavy oil fields [18] (often less than 3,000 ft (910 m)) can contribute to lower production costs; however, these are offset by the difficulties of production and transport that render conventional production methods ineffective. [18] Specialized techniques are being developed for exploration and production of heavy oil.
Production of heavy oil is becoming more common in many countries, with 2008 production led by Canada and Venezuela. [18] Methods for extraction include Cold heavy oil production with sand, steam assisted gravity drainage, steam injection, vapor extraction, Toe-to-Heel Air Injection (THAI), and open-pit mining for extremely sandy and oil-rich deposits.
With current production and transportation methods, heavy crudes have a more severe environmental impact than light ones. With more difficult production comes the employment of a variety of enhanced oil recovery techniques, including steam flooding and tighter well spacing, often as close as one well per acre. Heavy crude oils also carry contaminants. For example, Orinoco extra heavy oil contains 4.5% sulfur as well as vanadium and nickel. [19] However, because crude oil is refined before use, generating specific alkanes via cracking and fractional distillation, this comparison is not valid in a practical sense. Heavy crude refining techniques may require more energy input[ citation needed ] though, so its environmental impact is presently more significant than that of lighter crude if the intended final products are light hydrocarbons (gasoline motor fuels). On the other hand, heavy crude is a better source for road asphalt mixes than light crude.[ citation needed ]
With present technology, the extraction and refining of heavy oils and oil sands generates as much as three times the total CO2 emissions when compared with conventional oil, [20] primarily driven by the extra energy consumption of the extraction process (which may include burning natural gas to heat and pressurize the reservoir to stimulate flow). Current research into better production methods seek to reduce this environmental impact.[ citation needed ]
In a 2009 report, the National Toxics Network, citing data provided by the Carbon Dioxide Information Analysis Center of the government of the United States and the Canadian Association of Petroleum Producers (CAPP), stated that emissions of CO2 per unit of energy produced were ~84% of those for coal (0.078/0.093) - higher than CO2 emissions of conventional oil. [21]
Environmental Research Web has reported that "because of the energy needed for extraction and processing, petroleum from Canadian oil sands has higher life cycle emission" compared with conventional fossil fuels; "up to 25% more." [22]
Most[ quantify ][ weasel words ] geologists[ who? ] agree[ where? ] that crude becomes 'heavy' as a result of biodegradation, in which lighter oils are preferentially consumed by bacterial activity in the reservoir, leaving heavier hydrocarbons behind.[ citation needed ] This hypothesis leans heavily on the techniques of petroleum geochemistry. Poor geologic reservoir sealing exposes the hydrocarbons to surface contaminants, including organic life (such as bacteria) and contributes to this process.[ citation needed ]
Heavy oil can be found in shallow, young reservoirs, with rocks from the Pleistocene, Pliocene, and Miocene [18] (younger than 25 million years). In some cases, it can also be found in older Cretaceous, Mississippian, and Devonian reservoirs. These reservoirs tend to be poorly sealed, resulting in heavy oil and oil-sands.[ citation needed ]
Heavy oil is asphaltic and contains asphaltenes and resins. It is "heavy" (dense and viscous) due to the high ratio of aromatics and naphthenes to linear alkanes and high levels of NSOs (nitrogen, sulfur, oxygen and heavy metals). Heavy oil has a higher percentage of compounds with over 60 carbon atoms and hence a high boiling point and molecular weight. For example, the viscosity of Venezuela's Orinoco extra-heavy crude oil lies in the range 1000–5000 cP (1–5 Pa·s), while Canadian extra-heavy crude has a viscosity in the range 5000–10,000 cP (5–10 Pa·s), about the same as molasses, and higher (up to 100,000 cP or 100 Pa·s for the most viscous commercially exploitable deposits). [2] A definition from the Chevron Phillips Chemical company is as follows:
The "heaviness" of heavy oil is primarily the result of a relatively high proportion of a mixed bag of complex, high molecular weight, non-paraffinic compounds and a low proportion of volatile, low molecular weight compounds. Heavy oils typically contain very little paraffin and may or may not contain high levels of asphaltenes. [23]
Heavy crude oil is generally categorized in two ways[ citation needed ]:
Bitumen is an immensely viscous constituent of petroleum. Depending on its exact composition it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In the U.S., the material is commonly referred to as asphalt. Whether found in natural deposits or refined from petroleum, the substance is classed as a pitch. Prior to the 20th century the term asphaltum was in general use. The word derives from the ancient Greek ἄσφαλτος ásphaltos, which referred to natural bitumen or pitch. The largest natural deposit of bitumen in the world is the Pitch Lake of southwest Trinidad, which is estimated to contain 10 million tons.
Petroleum, also known as crude oil or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name petroleum covers both naturally occurring unprocessed crude oil and petroleum products that consist of refined crude oil.
Oil sands, tar sands, crude bitumen, or bituminous sands, are a type of unconventional petroleum deposit. Oil sands are either loose sands or partially consolidated sandstone containing a naturally occurring mixture of sand, clay, and water, soaked with bitumen, a dense and extremely viscous form of petroleum.
Synthetic crude is the output from a bitumen/extra heavy oil upgrader facility used in connection with oil sand production. It may also refer to shale oil, an output from an oil shale pyrolysis. The properties of the synthetic crude depend on the processes used in the upgrading. Typically, it is low in sulfur and has an API gravity of around 30. It is also known as "upgraded crude".
A visbreaker is a processing unit in an oil refinery whose purpose is to reduce the quantity of residual oil produced in the distillation of crude oil and to increase the yield of more valuable middle distillates by the refinery. A visbreaker thermally cracks large hydrocarbon molecules in the oil by heating in a furnace to reduce its viscosity and to produce small quantities of light hydrocarbons.. The process name of "visbreaker" refers to the fact that the process reduces the viscosity of the residual oil. The process is non-catalytic.
The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks.
An upgrader is a facility that upgrades bitumen into synthetic crude oil. Upgrader plants are typically located close to oil sands production, for example, the Athabasca oil sands in Alberta, Canada or the Orinoco tar sands in Venezuela.
Petroleum coke, abbreviated coke, pet coke or petcoke, is a final carbon-rich solid material that derives from oil refining, and is one type of the group of fuels referred to as cokes. Petcoke is the coke that, in particular, derives from a final cracking process—a thermo-based chemical engineering process that splits long chain hydrocarbons of petroleum into shorter chains—that takes place in units termed coker units. Stated succinctly, coke is the "carbonization product of high-boiling hydrocarbon fractions obtained in petroleum processing ". Petcoke is also produced in the production of synthetic crude oil (syncrude) from bitumen extracted from Canada's tar sands and from Venezuela's Orinoco oil sands.
Asphaltenes are molecular substances that are found in crude oil, along with resins, aromatic hydrocarbons, and saturates. The word "asphaltene" was coined by Boussingault in 1837 when he noticed that the distillation residue of some bitumens had asphalt-like properties. Asphaltenes in the form of asphalt or bitumen products from oil refineries are used as paving materials on roads, shingles for roofs, and waterproof coatings on building foundations.
Petroleum production in Canada is a major industry which is important to the overall economy of North America. Canada has the third largest oil reserves in the world and is the world's fourth largest oil producer and fourth largest oil exporter. In 2019 it produced an average of 750,000 cubic metres per day (4.7 Mbbl/d) of crude oil and equivalent. Of that amount, 64% was upgraded from unconventional oil sands, and the remainder light crude oil, heavy crude oil and natural-gas condensate. Most of the Canadian petroleum production is exported, approximately 600,000 cubic metres per day (3.8 Mbbl/d) in 2019, with 98% of the exports going to the United States. Canada is by far the largest single source of oil imports to the United States, providing 43% of US crude oil imports in 2015.
Steam-assisted gravity drainage is an enhanced oil recovery technology for producing heavy crude oil and bitumen. It is an advanced form of steam stimulation in which a pair of horizontal wells are drilled into the oil reservoir, one a few metres above the other. High pressure steam is continuously injected into the upper wellbore to heat the oil and reduce its viscosity, causing the heated oil to drain into the lower wellbore, where it is pumped out. Dr. Roger Butler, engineer at Imperial Oil from 1955 to 1982, invented the steam assisted gravity drainage (SAGD) process in the 1970s. Butler "developed the concept of using horizontal pairs of wells and injected steam to develop certain deposits of bitumen considered too deep for mining". In 1983 Butler became director of technical programs for the Alberta Oil Sands Technology and Research Authority (AOSTRA), a crown corporation created by Alberta Premier Lougheed to promote new technologies for oil sands and heavy crude oil production. AOSTRA quickly supported SAGD as a promising innovation in oil sands extraction technology.
Dilbit is a bitumen diluted with one or more lighter petroleum products, typically natural-gas condensates such as naphtha. Diluting bitumen makes it much easier to transport, for example in pipelines. Per the Alberta Oil Sands Bitumen Valuation Methodology, "Dilbit Blends" means "Blends made from heavy crudes and/or bitumens and a diluent, usually natural-gas condensate, for the purpose of meeting pipeline viscosity and density specifications, where the density of the diluent included in the blend is less than 800 kg/m3." If the diluent density is greater than or equal to 800 kg/m3, the diluent is typically synthetic crude and accordingly the blend is called synbit.
Canada's oil sands and heavy oil resources are among the world's great petroleum deposits. They include the vast oil sands of northern Alberta, and the heavy oil reservoirs that surround the small city of Lloydminster, which sits on the border between Alberta and Saskatchewan. The extent of these resources is well known, but better technologies to produce oil from them are still being developed.
Venezuela has the largest conventional oil reserves and the second-largest natural gas reserves in the Western Hemisphere. In addition Venezuela has non-conventional oil deposits approximately equal to the world's reserves of conventional oil. Venezuela is also amongst world leaders in hydroelectric production, supplying a majority of the nation's electrical power through the process.
Steam injection is an increasingly common method of extracting heavy crude oil. Used commercially since the 1960s, it is considered an enhanced oil recovery (EOR) method and is the main type of thermal stimulation of oil reservoirs. There are several different forms of the technology, with the two main ones being Cyclic Steam Stimulation and Steam Flooding. Both are most commonly applied to oil reservoirs, which are relatively shallow and which contain crude oils which are very viscous at the temperature of the native underground formation. Steam injection is widely used in the San Joaquin Valley of California (US), the Lake Maracaibo area of Venezuela, and the oil sands of northern Alberta, Canada.
Oil reserves in Canada were estimated at 172 billion barrels as of the start of 2015 . This figure includes the oil sands reserves that are estimated by government regulators to be economically producible at current prices using current technology. According to this figure, Canada's reserves are third only to Venezuela and Saudi Arabia. Over 95% of these reserves are in the oil sands deposits in the province of Alberta. Alberta contains nearly all of Canada's oil sands and much of its conventional oil reserves. The balance is concentrated in several other provinces and territories. Saskatchewan and offshore areas of Newfoundland in particular have substantial oil production and reserves. Alberta has 39% of Canada's remaining conventional oil reserves, offshore Newfoundland 28% and Saskatchewan 27%, but if oil sands are included, Alberta's share is over 98%.
Heavy oil production is a developing technology for extracting heavy oil in industrial quantities. Estimated reserves of heavy oil are over 6 trillion barrels, three times that of conventional oil and gas.
Located in northwest-central Alberta, the Peace River oil sands deposit is the smallest of four large deposits of oil sands of the Western Canadian Sedimentary Basin formation.
Bitumen froth treatment is a process used in the Athabasca oil sands (AOS) bitumen recovery operations to remove fine inorganics—water and mineral particles—from bitumen froth, by diluting the bitumen with a light hydrocarbon solvent—either naphthenic or paraffinic—to reduce the viscosity of the froth and to remove contaminants that were not removed in previous water-based gravity recovery phases. Bitumen with a high viscosity or with too many contaminants, is not suitable for transporting through pipelines or refining. The original and conventional naphthenic froth treatment (NFT) uses a naphtha solvent with the addition of chemicals. Paraffinic Solvent Froth Treatment (PSFT), which was first used commercially in the Albian Sands in the early 2000s, results in a cleaner bitumen with lower levels of contaminates, such as water and mineral solids. Following froth treatments, bitumen can be further upgraded using "heat to produce synthetic crude oil by means of a coker unit."
Carabobo is an oil field located in Venezuela's Orinoco Belt. As one of the world's largest accumulations of recoverable oil, the recent discoveries in the Orinoco Belt have led to Venezuela holding the world's largest recoverable reserves in the world, surpassing Saudi Arabia in July 2010. The Carabobo oil field is majority owned by Venezuela's national oil company, Petroleos de Venezuela SA (PDVSA). Owning the majority of the Orinoco Belt, and its estimated 1.18 trillion barrels of oil in place, PDVSA is now the fourth largest oil company in the world. The field is well known for its extra Heavy crude oils, having an average specific gravity between 4 and 16 °API. The Orinoco Belt holds 90% of the world's extra heavy crude oils, estimated at 256 billion recoverable barrels. While production is in its early development, the Carabobo field is expected to produce 400,000 barrels of oil per day.
