PanCanadian originally pursued thermosyphon technology to lower operating costs. However, it is now apparent that a more significant benefit is reduction of greenhouse gas (GHG) emissions. Other benefits include loss management, increased safety, improved operability and maintenance cost reduction.
A prototype Thermflo ™ thermosyphon process heater was developed by Hudson Products Corporation (HPC) as a joint effort with PanCanadian Petroleum Ltd. The unit was installed in a 320 m3 atmospheric heavy oil tank in northeastern Alberta in November '97. Performance testing was carried out over the next several months and evaluated using API Standards & Recommended Practices.
The testing was carried out in two phases. In phase one, we compared the performance of the thermosyphon to a naturally drafted venturi style nozzle burner in a firetube located in an adjacent tank. Both units were fired using sales utility gas. Increased combustion efficiency and improved heat transfer reduced fuel gas consumption by 33% and cut GHG emissions by 40%. In phase two of the testing, the prototype successfully burned solution gas normally vented to atmosphere. This translates to an annual operating cost saving of about $40,000 and GHG emission reduction of about 10,000 tonnes per year.
The thermosyphon process heater is a means of transferring heat from an external combustion chamber to liquid inside a process vessel or tank. It does this without having a flame within a firetube inside the vessel or tank and is therefore, significantly more efficient and safer than a firetube. Employment of a prototype heater in a heavy oil field production tank pilot project confirmed the concept and the improved efficiency lead to substantial reduction in GHG emission, lower operating costs and improved safety.
The preferred strategy of cold heavy oil reservoir exploitation in the Western Canadian Sedimentary Basin is to produce emulsion into field production tanks from wells drilled on a high density pattern, often at ten to twenty acre spacing. The emulsion is then trucked to a centralized cleaning facility, where it is processed to pipeline specification of 0.5' BS&W and 350 centistoke viscosity in preparation for transportation to refineries. Pipelining the emulsion directly to the cleaning plants is generally not feasible due to the sand cut, high viviscosity and entrained gas. The threat of bottom or side water breakthrough also introduces risk into the return on investment for pipelining.
Producing emulsion into field production tanks for trucking to cleaning plants has its own set of challenges. A property of low temperature heavy oil emulsion is high viscosity, which in turn lifts large amounts of sand and entrains gas with the oil. The entrained gas is in the form of expanding microbubbles that enhance fluid flow from the reservoir1,2. The microbubbles continue to expand in the tank, as the pressure drops to atmospheric. Here the gas slowly breaks out causing foam to sit on the oil in the tank. This foam layer can be several feet thick, increasing the risk of the tank overflowing and causing a spill.
