ECA Review Editorialist
Steam-assisted gravity drainage (SAGD) technology is the method Cenovus Energy uses to extract oil from oil sands buried too deep to mine. Their Foster Creek location currently produces 120,000 bbls/day and Christina Lake 58,000 bbls/day. The facilities are south of Fort McMurray and north of Cold Lake.
How it Works
SAGD uses steam to force oil to the surface. Multiple well pairs are drilled from one surface location. Each well pair consists of two horizontal wells drilled, one above the other, about five metres apart. The injector well heats the formation and softens the oil, allowing it to flow more freely. The oil and gas then drain into the producer well where it is pumped to the surface.
The effect of steam being forced down to produce oil is carefully watched. Throughout the Cenovus site, silver prisms dot the forest. “It works like Instar”, said Jason Abbate, Group Leader Production at the Christina Lake facility, “they talk to satellites that can then record surface movement.” Surface movement has been recorded between 20 and 60 mm.
There’s a lot of pressure happening with steam injection wells, “allowances are made so that well heads can move up and down about 19 inches” said Abbate.
“The SAGD process has several advantages over the traditional mining operation”, said Jessica Wilkinson, media advisor, and host for the weekly newspapers’ tour of Christina Lake on August 16, 2012.
A major advantage is the smaller footprint and less disturbance of the land when compared to mining operations. Sprinkled throughout the lease are cleared areas supporting well pads. Well pads usually have eight to twelve well pairs, that is, 16 to 24 wells. Approximately five to six square kilometers of forest is cleared to support each well pad, including roads. At the Foster Lake facility about three sections (750 hectares) is disrupted to produce approximately 120,000 barrels per day.
Pipelines carrying steam to the pads, and water, gas and oil from the pads to the plant, snake through the forest on above ground supports. Hidden cameras dot the lease recording animal movements. Using this information, wildlife paths have been provided over or under the pipelines.
Another advantage Cenovus has is their facilities use less steam to produce a barrel of oil than many of their competitors. Less steam means less water use, less natural gas used to create steam, and lower emissions of greenhouse gases.
Cenovus continues to explore alternate ways to reduce steam requirements. “At the Christina facility, solvent-assisted production (SAP) has been successfully piloted”, said Abbate. Butane, recovered from production wells, is captured and recycled to enhance recovery. Putting both water and butane down the injector wells has led to reduced steam requirements. Cenovus will be commercially introducing SAP at their Narrows Lake facility.
A concern with most industrial operations is their use of water. Water is a significant input variable for an operation that runs on steam. Some years ago, Cenovus switched from using fresh water and today all but five percent of water used is brackish. Salt water is found in deep underground reservoirs, is treated, then becomes the primary source to create steam. Their operation also provides for recycling and reuse of the majority of its process water.
There is a 70 percent recovery of oil from Cenvous’ steam injected wells and another 10 to 15 per cent recovered from wedge wells making the operation extremely efficient. Wedge wells are drilled close to the pads and draw up left over heated oils using the conventional method of pump jacks.
Jessica Wilkinson, communication advisor, said the “plant is put together like a big lego set”. Expansion modules (steam generators and heat exchangers) are assembled in Nisku as needed. The end product is very reliable since the same people and pattern are used. Expansion can increase incrementally and operations can be scaled up and down as needed. Also the phased approach allows improvements to be incorporated into future plant expansions.
The in-situ process now represents about half of all oil sands production, but will dominate the industry in the coming years in northern Alberta. With known technology, 80 percent of recoverable resources will be extracted by in-situ and 20 per cent by mining.
A number of companies are active in the area although none as large as Cenvous. Foster Creek is approved for 310,000 bbls/day, Christina Lake 300,000 bbls/day, and Narrows Lake 120,000 barrels of oil per day.
Suncor’s Firebag Operation is the next largest and it produces about 60,000 barrels per day.