The Saleski Pilot continues to be one of the most innovative thermal projects in the oil sands. The Pilot is unique in that it was built to improve on a proven extraction method - SAGD but quickly adapted to using only a single horizontal well for both injection of steam and production of emulsion - a technique called cyclic SAGD or C-SAGD.
There are two commonly used SAGD techniques that are both highly efficient at producing bitumen from the oil sands. One technique uses two parallel horizontal wells that are drilled into bitumen reservoirs below ground. Slowly, steam is pumped into the top injector well, heating the thick bitumen. As the bitumen warms up, gravity takes over. The mobilized bitumen drains down into the lower producer well that brings the bitumen back up to the surface for processing.
The second technique uses a single horizontal well that injects steam first, then produces from the same well in a cycling process C-SAGD under the same principles as dual-well SAGD – as the reservoir warms up, gravity forces the bitumen to flow down towards the well bore.
In both of these techniques, tailings ponds are not required.
Our source water for steam generation comes from the Lower Grand Rapids Formation. The Grand Rapids Formation is named for the spectacular Grand Rapids on the Athabasca River, which are produced by the river spilling over large concretions as the riverbed intersects the Lower Grand Rapids sand layer. The source water that comes from the Lower Grand Rapids Formation is not fit to drink or suitable for human, livestock or agricultural use.
The source water for the Saleski Pilot starts with the water source wells (WSW). We have two WSWs on the Pilot plant site, at the upper right of the Pilot plot plan diagram, with the remaining four wells about five kilometres west. The source water is pumped from the wells through a four-inch pipeline and into a source water tank located in the treatment tanks in the Tank Farm seen towards the left of the diagram. The wells are powered by a dedicated remote generator and controlled in the Control Room to the left of the Tank Farm.
The total production capacity of the wells is 1,600 m3 per day, supplying the pilot with the required 1,200m3 of water per day.
From the source water tank, the water is filtered and softened before arriving in the boiler feed water tank. The water then flows through heat exchangers that pre-heat the water from the hot production fluids before entering the boiler. There are two boilers, both 50MM BTU once through steam generator (OSTG),that creates 80 per cent quality steam.
As our C-SAGD wells utilize 100 per cent quality steam, the steam must first be separated in a high pressure steam separation module. From here, the 100 per cent quality steam flows to the wellhead metering skids located by the Wellhead Area to the right of the diagram. Steam condensate, known as blow down, from the high pressure steam separation module flows back through heat exchangers and to the boiler blow-down tank.
Any excess blow down containing residual dissolved solids is combined with regeneration and backwash wastes from water treatment and sent to the disposal tank in the Tank Farm. Water from the disposal tank returns via a pipeline to the three water disposal wells (WDW), one located near the WSW on the plant site and two others about five kilometres to the west.
Returning to the Wellhead Area, we have four production well-pairs (based on our initial plan to implement standard dual well SAGD), but currently only use one of the wells in each pair for C-SAGD operation. A fifth horizontal well was recently drilled and will shortly be used for injecting steam. Operations currently call for initial injection of steam into each of the wells and, after a period of 4-6 weeks, the same well is then turned over to production. Steam is re-injected once the production cycle has completed.
Oil water emulsion production from the well pairs flows initially to an inlet separation vessel, called the inlet degasser in the Inlet and Produced Gas Area. Production flows under sufficient pressure from the bottom hole pumps that little vapour is generated, so flows from the wells can be measured essentially as a liquid-only stream. At the first inlet vessel, the inlet pressure is adjusted to treatment pressure. Vapours, such as produced gas and evaporated solvent, flash into the produced gas system. Separating the produced gas is useful in that this gas can become a feedstock for the OTSG’s reducing the natural gas volume purchased to run the steam plant
Liquids from the inlet vessel are cooled, mixed with diluent and sent to the free water knock out (FWKO), located in the lower mid-right of the diagram. The FWKO removes all but about 10 per cent of the remaining water. The remainder then flows to the treater vessel to the left of the FWKO, where the water content is reduced to a pipeline specification of 0.5 per cent bottom solids and water.
The low-water-content oil now flows to the oil stabilizer, where temperature and vapour pressure of the product is reduced to that required for trucking or pipelining. The product is cooled to shipment temperature and sent to the dilbit storage tanks or bitumen blend tanks located at the left of the diagram in the Tank Farm. Bitumen blend is trucked from the Truck Loading and Unloading Area.
Meanwhile, back at the Inlet and Produced Gas Area at the centre of the diagram, vapours from the inlet degasser, the FWKO, the treater and the oil stabilizer are combined, cooled, and separated in the Solvent Area recycle process into natural gas; diluent for recycle; Propane for recycle; and water for disposal.
The plant has a high pressure flare stack used for emergency relief known as the Flare Knock Out.