Review of Thermal Recovery Methods

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract Oil displacement is less than perfect because despite driving forces - part of the original oil in place is retained by capillary and by viscous forces. The viscous forces can be reduced by heating the oil in place. Most of the heat is inevitably taken up by the oil sand, interbedded shales and cap- and base rock. The heat is therefore used most efficiently where a maximum of thermally recoverable oil is tied to a minimum of rock (heavy oil, high porosity etc.). The economy may be improved by recuperating heat from swept formation for repeated use. Besides reducing the retaining forces, thermal drive also enhances the driving forces because many reservoir volumes of hot water, steam or air are required to displace one volume of oil. For steam and air this enhancement is stronger the lower the pressure. In the initial phase, when the oil is still cold, it may be hard to obtain satisfactory circulation and special well patterns with a high number of producers per injector (inverted 9 spot, 13 spot) are sometimes used. These patterns also minimize pressure later on. Heat stimulation of producers is also used to facilitate start up. producers is also used to facilitate start up. Where heat recuperation is applied, the recovery-efficiency of the heat should also be considered and an overall sweep from the reservoir boundary may be preferred over a pattern flood. The heat may be applied from the surface by specially designed hot water heaters or steam generators. The injectors are subjected to high thermal stresses and in old fields, where more often than not additional wells have to be drilled, the new ones are invariably used as injectors. The compressed air for in situ combustion requires more expensive surface installations, but less fuel than hot water or steam. Heat recuperation is more efficient in combustion projects because it can be done continuously projects because it can be done continuously by simultaneous cold water injection. Wet combustion, with its double injection system requires more engineering than any other thermal drive: determination of optimum water/air ratio, evaluation of corrosion danger and where necessary its prevention.