Polyacrylamide and its derivatives for oil recovery

Figure 8. 
Schematic diagrams of pore occlusion mechanisms for membranes with 
smaller and larger pores compared to average gel particle sizes.
 
interstitial flow between particles. In our pore occlusion tests, upon microgel dispersion 
injection the gel particles formed a film on the top of membrane but there was not 
effective occlusion performance for pore membranes smaller than particles. 
Figure 9 shows SEM pictures of membranes recovered and observed after pore 
occlusion testing. While the original swollen microgels were saturated with water, the 
microgel particles flattened upon drying. Adjacent gel particles in the SEM images 
support steric hindrance of pore access by neighboring gel particles, which prevented 
more gel particles from occluding pores. Sterically limited access allowed higher flow 
through narrow pore membranes than larger, widely spaced pores compared to particle 
size. Thus the gels were most effective at occluding pores of size similar or larger than 
particle diameter, as observed by others.
22,30,31
The observation is significant toward 
Microgel
dispersion
Porous membrane
a. Smaller pore 
membranes
b. Larger pore 
membranes
Occluded pores
Pores open due to steric 
hindrance

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supporting the inability of larger particles to occlude smaller pores, which can prevent 
damage in oil well flow fields.
a) 
a)
b) 
Figure 9. 
SEM Picture of membranes after pore occlusion testing. a) membrane with 
nuclear pore size of 1.2 µm; b) membrane with nuclear pore size of 10 µm.
 
CONCLUSIONS 
A new water-free synthesis method was developed to polymerize polyacrylamide 
microgel above the melting point of the monomer. Little surfactant (2 wt.-% Span 85) 
was required in the synthesis and solvent was recyclable to reduce production cost. The 

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produced gel particles were dry microspheres and readily dispersed in water.
Comparable, microgels synthesized by traditional methods require post-treatments, like 
grinding and dehydrating, to produce dry powder gel particles. 
In this paper, two different crosslinkers were employed to give the synthesized 
particles thermally responsive properties with two stages of aqueous size expansion. The 
average diameter of the microspheres was 7µm. After fully swollen in water at room 
temperature, the microgel’s average diameter had increased to about 20 times the original 
size. At a higher temperature stimuli of 80 º
C, the average volume of the water saturated 
microgels swelled to 160 times larger than the original volume. The higher temperature 
induced cleavage of the labile PEGMA crosslinker but also stable crosslinker and/or 
induced chain scission, which was observed as a cyclic dimer molecule. During the 
process from synthesis through dispersion and water absorptive swelling, the shape of the 
microgel particles was spherical. 
Pore occlusion performance of the microgels was studied by a membrane model.
The relationship between the microgel particle size and the membrane pore size as well 
as the membrane pore separation density were important factors for occlusion efficiency.
If the size of gel particles was much larger than the pore size and the pitch of pores, they 
did not produce effective occlusion of filtrate flow. The lack of efficiency appears to be 
due to steric hindrance of adjacent particles preventing occlusion of nearby pores.
Swollen microgels sealed the nuclear pores with effective pore occlusion when size 
matched and of average size similar to or smaller than the membrane pores and pore 
separation. 

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