The recovery of bitumen from oil sands deposits, such as those at Cold Lake, Alberta, is ultimately dependent on the ability to inject large amounts of steam into the ground. Oilfield steam generators have been used to provide this steam for many years in heavy oil fields in California, Venezuela and Western Canada. This paper describes some of the factors to be considered in the design, construction and operation of these once-through steam generators. In particular, the design parameters which define the size, shape and ultimate performance of very large steam generators will be outlined with reference to some of Esso Resources Canada Limited's requirements for the Cold Lake area. One of these requirements is that the generators must be designed to permit the reuse of produced water, an essential water conservation measure.
Esso currently has three of the largest once through generators in the world installed at the Leming Pilot Plant near Cold Lake. Two of these units have been in continuous operation for over two years, generating steam from treated produced water. A third unit was installed in December of 1983. These units are prototypes of the steam generators to be installed in the phased Cold Lake Production Project (CLPP) which is currently under construction.
This paper discusses the design considerations for very large steam generators, such as those which Esso is currently using at Cold Lake. Many steams generator vendors in the past have given written papers on the same topic. However, I will be addressing the design from the point of view of the end user, rather than the supplier.
First, I will review the general reservoir and process requirements which set the basic design parameters in all oilfield steam generator applications. Secondly, I will review the main steam generator design parameters which define the size, shape, performance and operation of steam generators for thermal recovery operations. This will include some discussion of the basis for the specifications of the very large steam generators installed at Esso's Pilot Plants and planned for our Cold Lake Commercial development. Finally, I will review some of the equipment options which are available on the market, and where these options can best be applied.
The main design parameters are usually specified by the Reservoir Engineers and Geologists who evaluate potential oil sands leases for possible development. After finding a suitable site for a heavy oil production project, they have to come up with a development plan. They decide how many wells will be drilled, the pattern of drilling and spacing. Usually, the capacity of the steam generation facility will then be based upon a calculated injection rate per well or an overall expected oil/steam ratio. As well as capacity, they would also decide on an injection pressure and steam quality (i.e. the percent of the injected water that is in the vapor phase). If the reservoir oil is mobile, a steam flood may be suitable with relatively low injection pressures, rates and steam qualities to aid displacement and prevent steam breakthrough.