Heavy crude oil
[3] When reservoir viscosity measurements are not available, extra-heavy oil is considered by the WEC to have a lower limit of 4° API.
At that time Venezuela began authorizing "joint ventures to upgrade the extra-heavy crude resources.
Generally, a diluent is added at regular distances in a pipeline carrying heavy crude to facilitate its flow.
[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.
On the other hand, large quantities of heavy crudes have been discovered in the Americas, including Canada, Venezuela and California.
[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.
[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.
[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.
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.
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).
Heavy oil has a higher percentage of compounds with over 60 carbon atoms and hence a high boiling point and molecular weight.
[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.
