Cyclic Steam Stimulation (CSS) has been a commercial recovery process since the mid 1980's in the Cold Lake area in northeast Alberta. The current bitumen production is over 220,000 bbl/d using CSS from this area. To achieve desired injectivity in the bitumen saturated reservoir, steam is usually injected at a pressure above or close to the fracture pressure of the formation. A relatively high pressure drawdown is created between the wellbore and formation during the production phase, particularly in the early stage of the production cycle where formation compaction and solution gas drive are the two most important recovery mechanisms. The CSS process has limited application in reservoirs with thick bottom water or in reservoirs with fine grain sands.
The Steam Assisted Gravity Drainage (SAGD) process has been field tested and commercially expanded in the Lower Grand Rapids and Clearwater Formations in the Cold Lake area. In contrast to CSS, SAGD is a continuous steam injection process that relies on "gravity" and requires a minimum pressure drawdown to drive the reservoir fluids to the wellbore. This provides a significant advantage for SAGD as an option for the reservoirs with bottom water, top gas or with formations with fine grain sands. Several SAGD projects are in operation in different types of reservoirs in the Cold Lake and Lloydminster areas; some with thick bottom water zones.
A performance review is conducted based on the available data for various CSS and SAGD projects in the Cold Lake area. The selection criteria between CSS and SAGD technologies for Clearwater and Lower Grand Rapids are discussed. Reservoir modeling results are presented concerning the impact of well placement, reservoir heterogeneity and operating parameters on SAGD performance, based on Osum's Lower Grand Rapids and Clearwater geology in the Cold Lake area.
The Clearwater Formation is the main reservoir focus for thermal commercial development in the Cold Lake area. The Grand Rapids Formation is a secondary thermal reservoir. To date there is one commercial development in the Lower Grand Rapids Formation in the Cold Lake area. Figure 1 shows a Cold Lake location map where the four major operators are IOL, CNRL, Husky and Shell. Osum Oil Sands Corp. is a relatively new participant in the development of Cold Lake bitumen resources. Its leases are also displayed in Figure 1.
The development of the Clearwater Formation in the Cold Lake area can be divided into the following stages :
laboratory testing and research piloting from 1960 to 1970;
field demonstration pilot testing from late 1970s to mid 1980s and
commercial CSS operations since mid 1980s.
IOL and CNRL are the two biggest thermal operators in this area utilizing the CSS process, with a combined total bitumen production of 210,000 bbl/d by the end of 2007 [1, 2].
Pilot testing of SAGD in the Clearwater Formation commenced in the late 1990s at Burnt Lake and Hilda Lake. The Burnt Lake pilot has three well pairs and Hilda Lake has two well pairs .