There are a number of ways to access heavy oil and bring it to the surface
These methods are generally broken down into three categories: primary, secondary, and tertiary. The selection of any of these methods will depend on multiple 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 methods
Primary recovery occurs when the energy used to expel oil comes from the expansion of a gas cap overlying the oil, pressure support from an active aquifer, gravity drainage, dissolved gas being expanded and freed in the formation—or a combination of two of these methods. Falling into the “cold production” category, these methods are commonly referred to as “natural lift,” and have a recovery factor of approximately 5-10% for certain heavy oils (versus around 30% for conventional oil). A variant to cold production methods is cold heavy oil production with sand (CHOPS) where deliberately producing sand along with the oil creates wormholes or voids in the producing zone that attract more oil toward the wellbore.
Secondary recovery methods
When natural lift methods are no longer sufficient—which will result in insufficient underground pressure to bring the oil to the surface—secondary recovery methods that are still in the cold production category come to the fore. In effect, these methods involve injecting external energy sources into the reservoir to produce the missing pressure. These artificial methods include water injection, natural gas reinjection and CO2 injection. Including primary recovery methods, total oil recovery will range from 10-20% on average in most heavy oils.
Tertiary (EOR) recovery methods
Tertiary is also referred to as EOR (enhanced oil recovery) which is accomplished via thermal and non-thermal means. When heavy oil reaches a certain weight, and secondary methods fail, non-thermal or thermal tertiary methods are employed. Non-thermal methods include microbial and CO2 flooding. But heat—primarily via steamflooding—is the most favored and effective method of inducing more oil to flow. Steam is injected into the injector well to help “heat” the oil and force it to the surface via the producer well. Cyclic steam stimulation (CSS), also known as “huff-and-puff” or steam soak, involves using a single well to inject steam into the reservoir over a period of months, with cycle soak times of weeks. With CSS, it is condensation, not heat, that precipitates oil flow. Toe to heel air injection (THAI) is a method that employs combustion—which liquefies the heavy oil so it can be extracted from the reservoir. One of the most successful and best known methods of tertiary thermal recovery is steam-assisted gravity drainage (SAGD) process, which has returned production efficiencies up to 60% or better in Canadian heavy oil reservoirs.
Used for bitumen (ultra heavy oil). Found at depths generally shallower than 75 meters, the viscosity of certain bitumen deposits can be higher than 10,000 centipoise. At this viscosity, the oil is bonded to sand, forming a semi-solid that is actually mined, and then transported by truck for processing and refining. Approximately 10% of bitumen deposits found in Canada are recoverable via mining. Additional quantities are extracted using in-situ methods.