Problems in Applying Thermal Processes

The main technical problems associated with thermal techniques are poor sweep efficiencies, loss of heat energy to unproductive zones underground, and poor injectivity of steam or air. Poor sweep efficiencies are due to the density differences between the injected fluids and the reservoir crude oils. The lighter steam or air tends to rise to the top of the formation and bypass large portions of crude oil. Data have been reported from field projects in which coring operations have found significant differences in residual oil saturations in the top and bottom parts of the swept formation. Research needs to be conducted on methods of reducing the tendency for the injected fluids to override the reservoir oil. Techniques involving foams are being employed.

Large heat losses continue to be associated with thermal processes. The wet combustion process has lowered these losses for the higher temperature combustion techniques, but the losses are severe enough in many applications to prohibit the combustion process. The losses are not as large with the steam processes because they typically involve lower temperatures. The development of a feasible downhole generator will significantly reduce the losses associated with steam-injection processes.

The poor injectivity found in thermal processes is largely a result of the nature of the reservoir crude oils. Operators have applied fracture technology in connection with the injection of fluids in thermal processes. This has helped in many reservoirs.

Operational problems include the following: the formation of emulsions, the corrosion of injection and production tubing and facilities, and adverse effects on the environment. When emulsions are formed with heavy crude oil, they are very difficult to break. Operators need to be prepared for this. In the high-temperature environments created in the combustion processes and when water and stack gases mix in the production wells and facilities, corrosion becomes a serious problem. Special well liners are often required. Stack gases also pose environmental concerns in both steam and combustion applications. Stack gases are formed when steam is generated by either coal- or oil-fired generators and, of course, during the combustion process as the crude is burned.