Thermal Recovery Methods
There are two main approaches to oil sands and heavy oil development; in-situ and mining. The method used depends on several factors including; fluid characteristics, rock properties and reservoir depth.
In-situ processes are employed in deeper deposits. They extract the bitumen from the sand by injecting steam, or sometimes fluids. The bitumen becomes mobile and is produced to surface through wells drilled into the deposit. In-situ methods vary from 18 to 60% efficiency depending on such factors as the geological characteristics and complexity of the formation, and the fluid characteristics of the heavy oil such as viscosity and density. In-situ processes have a much smaller footprint on the land than mining projects.
Surface mining is used for shallower bitumen deposits. Overburden is first stripped off to expose the bitumen formation and the oil sands are mined. The oil sands are then conveyed to a cleaning facility where the sand is mixed with warm water and chemicals to separate out the bitumen. Surface mining can recover 90% of the bitumen-in-place by surface.
The most common in-situ processes are thermal recovery methods. Basically, steam is injected through wells to heat the bitumen and make it mobile enough to flow to production wells. These thermal recovery methods include:
- Cycling Steam Stimulation (CSS)
- Steam Flooding (SF)
- Steam Assisted Gravity Drainage (SAGD)
CSS and SF generally target thicker and deeper bitumen deposits, situated more than 400 metres below surface. SAGD typically targets intermediate-depth deposits, located less than 400 metres below surface, with relatively high sand permeability.
Cycling Steam Stimulation
In CSS, steam is injected at high pressure and temperature (as high as 350°C) into the oil sand formation for several weeks. Steam helps recover the resource in several ways. The heat dramatically reduces the viscosity of the oil sands and the water vapour helps to break out the bitumen from the sand that contains it. The high pressure induces fractures to be formed in the formation, through which steam can penetrate the oil sands. After a portion of the reservoir has been invaded and saturated, the steam is turned off and the reservoir is allowed to soak for several weeks. Then, the injection wells are turned into production wells. The mixture of condensed water and mobilized bitumen either flows on its own uphole to surface, or is pumped to the surface using downhole pumps activated by pumpjacks at surface. When the rate of production starts to decline, the injection-soak-production cycle is repeated. It can take between 120 days and two years to complete a single cycle. At surface, the cooling bitumen is typically mixed with diluents to reduce its viscosity and allow its transportation by pipeline.
Canada's oldest and largest in-situ CSS bitumen recovery project is Imperial Oil's Cold Lake in northeastern Alberta. Bitumen production averaged more than 24 000 cubic metres per day in 2007 from approximately 4 000 wells. This was approximately 40% of Canada's total in-situ production, or about 5% of total Canadian oil production.
Steam Flooding
SF is also a steam-based process. It involves continuous injection of steam into vertical injector wells. The steam mobilizes the heated bitumen and drives it towards production wells. However, recovery efficiencies are generally poor due to gravity override of the steam over the bitumen, hence a significant amounts of the oil is bypassed. With bitumen recovery typically less than 20% even in the best bitumen deposits, SF is not a common bitumen recovery process.
Steam Assisted Gravity Drainage
SAGD typically relies on two horizontal wells drilled near the base of the reservoir formation with a vertical separation of several metres. Steam is injected into the reservoir through the upper well. As the steam rises and condenses, it heats up the bitumen, reducing its viscosity. A “heat chamber” is created, which allows the hot bitumen and condensed steam (water) to drain by gravity into the lower producing well. The mobile bitumen then flows or is pumped up to surface.
Three SAGD projects currently exist:
- The $3.5 billion Long Lake project is operated by NEXEN and OPTI Canada in the Athabasca area. It is the first in-situ integrated oil sands project in that bitumen will be upgraded in a field processing facility. The project will use synthetic gas from internally-produced asphaltenes for fuel, eliminating the need to rely on purchased natural gas. Phase 1 development includes approximately 12 000 cubic metres per day of bitumen production from 81 SAGD well pairs. Recovered bitumen will be converted into approximately 9 600 cubic metres per day of premium synthetic crude oil and products via onsite upgrading. First steam for SAGD operations is now on all well pads.
- Suncor Energy's Firebag uses recycled water to generate steam in a closed loop system. Production began in 2004 at an average of 1 590 cubic metres per day and increased to an average of 6 000 cubic metres per day in 2007. The target is for 22 000 cubic metres per day in 2010.
- Japan Canada Oil Sands (JACOS) has operated its Hangingstone demonstration operation for nine years. The SAGD operation is one of the longest running in the Athabasca area. Current production is approximately
1 300 cubic metres per day.
New Technologies
New technologies continue to improve project economics and reduce environmental impacts from bitumen recovery operations. Examples of these advanced technologies include:
- Solvent-assisted processes - Imperial Oil has recently applied a solvent-assisted CSS process called LASER, which reduces bitumen viscosity by adding solvent to the reservoir formation.
- ES-SAGD “Expanding Solvent-SAGD” - developed by the Alberta Research Council. This is a steam-based hybrid process involving the addition of a solvent or mixture of solvents to the steam. Advantages include further reduction of bitumen viscosity and reduced steam utilization.
- N-Solv Corporation - employs in-situ solvent extraction of the bitumen from oil sands. The process utilizes heated solvents, without steam injection, in a similar well configuration as SAGD. Without steam, heating requirements and fuel costs are believed to be much lower than SAGD.
In-situ combustion is also a potential candidate for improving project economics and significantly reducing environmental impacts. The most promising is Toe-to-Heal-Air-Injection (THAI). This technique consists of two wells: a horizontal producer situated at the bottom of the producing formation, and a vertical air injector at the toe of the producer. Initially, the formation near the vertical injector is super-heated to the spontaneous ignition temperature. Then air injection is started using the vertical well, resulting in in-situ combustion. The combustion reduces the viscosity of the surrounding bitumen and allows it to drain into the producer. The combustion chamber progresses along the horizontal producer, starting from the toe towards the heel of the producer. The produced CO2 remains in the reservoir. This method is currently being tested by Petrobank at Whitesands. Bitumen production rates are in the range of 130 cubic metres per day per well. Petrobank is planning a commercial project with an initial rate of 16 000 cubic metres per day of bitumen production.
