Page 87 - Principles of Catalyst Development

68 Principles of Applied Reservoir Simulation

modern reservoirs incorporate pressure maintenance early in the production life
of the field, sometimes from the beginning of production. In this case the
reservoir is not subjected to a conventional primary production phase. The term
"pressure maintenance" is a more accurate description of the reservoir
management strategy for these fields than the term "secondary production."

Alternative Classifications
Both primary and secondary recovery processes are designed to produce
oil using immiscible methods. Additional methods may be used to improve oil
recovery efficiency by reducing residual oil saturation. The reduction of residual
oil saturation requires a change in such factors as interfacial tension or
wettability. Methods designed to reduce residual oil saturation have been referred
to in the literature as:
• Tertiary Production
• Enhanced Oil Recovery
• Improved Oil Recovery
The term tertiary production was originally used to identify the third stage of
the production life of the field. Typically the third stage occurred after water-
flooding. The third stage of oil production would involve a process that was
designed to mobilize waterflood residual oil. An example of a tertiary production
process is a chemical flood process such as surfactant flooding. Tertiary
production processes were designed to improve displacement efficiency by
injecting fluids or heat. They were referred to as enhanced recovery processes.
It was soon learned, however, that some fields would perform better if the
enhanced recovery process was implemented before the third stage in the life
of the field. In addition, it was found that enhanced recovery processes were
often more expensive than just drilling more wells in a denser pattern.
The drilling of wells to reduce well spacing and increase well density is
called infill drilling. The birth of the term "infill drilling" was coincident with
the birth of another term, "improved recovery." Improved recovery includes
enhanced oil recovery and infill drilling. Some major improved recovery
processes are waterflooding, gasflooding, chemical flooding, and thermal
recovery, [Dyke, 1997]. They are discussed in more detail below.