ABSTRACT
The recovery of oil from a reservoir can be divided into three stages. In the primary oil recovery process, oil is recovered due to the pressure of natural gases, which forces the oil out through production wells. When this pressure decreases to a point where it is no longer capable of expelling the oil, water is injected to repressurize the reservoir. This is generally called secondary oil recovery or water flooding. The average oil recovery during the primary and secondary stages is nearly 35% of oil-in-place. The purpose of the tertiary (enhanced) oil recovery process is to recover at least part of the remaining oil-in-place. Enhanced oil recovery (EOR) methods can be divided into two major groups: thermal processes and chemical flooding processes. In situ combustion, steam injection, and wet combustion methods fall into the first category, whereas caustic flooding, surfactant flooding, micellar polymer flooding, and CO2 flooding fall into the second category of processes [1–5].
