Recovery Methods

An overview of recovery methods

Select an icon above to learn more on each method.

Heavy crude oil is generally defined as any liquid petroleum with an API gravity less than 22.3°. It is formed as a result of the oil being degraded, resulting in the loss of its lighter hydrocarbon fractions with the heavier fractions remaining. Heavy oil typically has a viscosity greater than 10 centipoise, and extra heavy oil is generally referred to as heavy oil with a viscosity in excess of 10,000 centipoise. Heavy oil has higher contents of asphaltenes, heavy metal, sulphur, and nitrogen and it requires special refining processes.

Heavy oil can be found in more than 30 countries, with some of the world's largest reserves located in Venezuela and Canada. Heavy crude oil is also associated with bitumen found in oil sands; the main difference is that bitumen is very viscous and generally does not flow under normal production methods. Canada has large reserves of oil sands.

Heavy oil recovery methods include primary production, thermal production, and cold enhanced oil recovery (EOR). The selection of any of these methods will depend on many factors, including the stage of reservoir production, formation and fluid properties, reservoir geology, available production and transportation facilities, and the underlying heavy oil economics in a particular region.

Primary Recovery
Primary recovery is the first stage of heavy oil production in which natural reservoir energy, such as gravity drainage, displaces hydrocarbons from the reservoir into the wellbore and up to surface. But as reservoir pressure declines because of production, it is necessary to implement an artificial lift system such as a rod pump or electrical submersible pump. Cold heavy oil production with sand (CHOPS) is another primary recovery technique involving the continuous production of sand to improve the recovery of heavy oil from the reservoir.

Cold EOR
Cold EOR is the recovery of heavy oil using nonthermal methods including production from horizontal and multilateral wells with water, solvent, and gas injection. Waterflooding is the most common nonthermal EOR approach which involves the injection of water to displace the heavy oil. Another nonthermal process known as vapor extraction (VAPEX) involves the injection of a solvent vapor to reduce the viscosity and improve the mobility of the heavy oil.

Thermal
Thermal methods typically involve the injection of steam or hot water into the reservoir to improve the mobility of the heavy oil and provide a displacement mechanism. Thermal methods provide some of the highest recovery factors, but they also have the largest potential capital expenditure and operating costs. Three common and proven thermal production methods are considered below.

• SAGD
  Using pairs of parallel wells—one a steam injector and the other a producer—steam is injected into the top well; the resulting steam chamber encourages heated oil to drain into the lower well.
• Cyclic Steam Stimulation (CSS)
  A single well is used to inject steam into the reservoir, both to heat the oil and to reduce its viscosity. After the reservoir has been through a soak phase, the operation of the injector well is reversed to produce the oil. This technique is also known as huff 'n’ puff.
• Steam Flood
  Two vertical wells are used. One injects steam into the reservoir, creating a steam front that sweeps the oil before it into the producer well.