Crude oil is a naturally-occurring substance found in certain rock formations in the earth. To extract the maximum value from crude, it needs to be refined into petroleum products. The best-known of these is gasoline, or petrol. Others include liquefied petroleum gas (LPG), naphtha, kerosene, gas oil and fuel oil.
Oil wells are used to release the oil from within the earth. Some of the earliest developed oil wells were drilled in China using bamboo poles. These oil wells were developed in 347 A.D. for the sole purpose of providing enough fuel to create a thriving salt industry. By the 1950s, crude oil became a global energy source, which in effect killed the whaling industry by making whale oil obsolete.
In the crude oil industry, there are oil names (such as Brent Light Crude Oil and Bonny Light) and there are oil types (such as light, heavy, sweet and sour). Light oil has a low density viscosity, while heavy oil is of higher density. Sweet oil has less sulfur, and sour oil has excessive sulfur. The world market prefers light, sweet crude oil, largely because it requires less refinement and production time before going to market.
Light vs. Heavy Crude Oil:
Light Crude oil is liquid petroleum that has low density and that flows freely at room temperature. It has low viscosity, low specific gravity and high API gravity due to the presence of a high proportion of light hydrocarbon fractions. It generally has a low wax content as well. On the other hand, heavy crude oil or extra heavy crude oil is any type of crude oil which does not flow easily. 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 API gravity less than 20°. Extra heavy oil is defined with API gravity below 10.0 °API (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. )
Light crude oil receives a higher price than heavy crude oil on commodity markets because it produces a higher percentage of gasoline and diesel fuel when converted into products by an oil refinery. Heavy crude oil has more negative impact on the environment than its light counterpart since its refinement requires the use of more advanced techniques and the use of contaminants.
The sweet light crude oil Western Texas Intermediate (WTI) is used as a benchmark in oil pricing.
Heavy crude oil:
Heavy crude oil or extra heavy crude oil is any type of crude oil which does not flow easily. 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°. Physical properties that differ between heavy crudes lighter grades include higher viscosity and specific gravity, as well as heavier molecular composition. Extra heavy oil is defined with a gravity of less than 10° API (i.e. with density greater than 1000 kg/m 3 or, equivalently, a specific gravity greater than 1 and a reservoir viscosity of no more than 10,000 centipoises. With a specific gravity of greater than 1, extra heavy crude is present as a dense non-aqueous phase liquid in ambient conditions.
Heavy crude oil is closely related to natural bitumen from oil sands. Some petroleum geologists categorize bitumen from oil sands as extra heavy crude oil due to the density of less than 10 °API. Other classifications label this as bitumen differing it from extra-heavy oil. They differ in the degree by which they have been degraded from the original crude oil by bacteria and erosion. Often, bitumen is present as a solid and does not flow at ambient conditions.
The largest reserves of heavy crude oil in the world are located north of the Orinoco river in Venezuela, the same amount as the conventional oil reserves of Saudi Arabia, but 30 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 pipeline carrying heavy crude to facilitate its flow.
Economics:
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 USGS updated the Orinoco deposits (Venezuela) recoverable value to 513 billion barrels (8.16×10 10 m 3 ) making this area the one of the world's largest recoverable oil deposit. 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. Technology utilized for the recovery of heavy oil has steadily increased recovery rates.
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 (often less than 3000 feet) can contribute to lower production costs; however, these are offset by the difficulties of production and transport that render conventional production methods ineffective. Specialized techniques are being developed for exploration and production of heavy oil.