Polyacrylamide and its derivatives for oil recovery

1.
 
PREFACE 
Crude oil is an important commodity raw material for the energy and chemical 
industries. In spite of continued investment and advances in exploiting alternative energy 
sources, oil and natural gas will continue to be a significant portion of US and global 
energy portfolios for decades. [1] In the first (primary) stage of oil recovery, the oil is 
displaced by its own reservoir energy, such as gas drive, water drive, or gravity drainage. 
In the second stage, external fluids such as water or gas were injected into the reservoir to 
maintain the necessary pressure and displace the oil towards to the production wells. 
After the secondary oil recovery, there are still two thirds[2] of the original oil left in the 
reservoir and in most cases, 40-50% of the original oil in place (OOIP) [3] is not 
produced (see Figure 1.1.). The tertiary oil recovery, also named the enhanced oil 
recovery (EOR) uses unconventional chemical methods that target the oil volume 
remaining in reservoirs after conventional-recovery methods. [4-6]
Figure 1.1.
 
Oil production in different stages[4, 5]
It has been proven in field projects that chemical flooding (Figure 1.2.), in 
especial, polymer flooding is an effective method to improve the oil yield. [7, 8] A 

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2 
typical polymer flood project involves mixing and injecting polymer over an extended 
period of time until 1/3~1/2 of the reservoir pore volume has been injected. When water 
is injected into a reservoir, it prefers to follow the path of least resistance to flow 
(usually the layers with higher permeability) directly to the lower pressure region of the 
offset producing wells. If the oil in place has a higher viscosity than the injected water, 
the water will finger through this oil and bypass it. It will result in a lower sweep 
efficiency and a loss in recovery. [9] The EOR principle of polymer flooding is to 
increase water viscosity and thus reduce the water/oil, mobility ratio defined as 
(krw/uw)/(kro/uo) (kro=relative permeability to oil, krw=relative permeability to water, 
uo=viscosity of oil, uw=viscosity of water) so that the “swept” volume of the petroleum 
reservoir is increased. Polymer flooding has been applied successfully and has 
improved oil recovery by 5 to 15% of original oil in place. [1, 9]
Figure 1.2.