Polyacrylamide and its derivatives for oil recovery

partially seal a formation region.
9,10,14
PPGs, on the other hand, are prepared before 
injection. PPGs are crosslinked, dry particulate hydrogels, that can expand tens or 
hundreds times of their original size when dispersed in water.
10
Polyacrylamides are the 
main polymers used for preparing PPGs due to acrylamide’s cost, facile polymerization, 
polyacrylamide aqueous solution properties, and gelling capability of the polymer. 
Two main methodologies have been adopted in synthesis of polyacrylamide 
PPGs. The first method is solution polymerization
20
, which requires all monomers, 
crosslinkers, and waterborne initiator are added to solvent, typically water to form a bulk 
gel. The obtained bulk gel is then dried and cut or ground into dry particle gels, which 
are dispersed in water as an injectable gel particle dispersion. Bai, et al.
8,9,12-17,21
have 
conducted synthesis, lab tests and pilot testing, as well as field applications of bulk PPGs. 
A second method to synthesize PPGs is through inverse suspension 
polymerization,
22-24
with water, a hydrophobic non-polar solvent, surfactants, and 

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initiator to form a water in oil (w/o) system to synthesize polyacrylamide microgels.
Waterborne or oil soluble initiators could be used to initiate free radical polymerization 
through different mechanisms. Microgels prepared by this method have been studied in 
EOR application for several years.
25,26
For instance, Wang, et al.
27
reported a 
polyacrylamide EOR nanogel with an original diameter of approximate 50 nm that 
expanded to several micrometers upon swelling in pure water.
PPG microgels synthesized by traditional polymerization mentioned above need 
energy intensive post-treatment to isolate from water phase into dry particles. In this 
paper, a novel PPG synthesis method is developed based on an inverse suspension 
polymerization but in the absence of water. Dry product powder is obtained by 
polymerization above the melting point of the monomer. In this way, the products are 
dry solid microspheres, readily separated from solvent. Compared to traditional inverse 
suspension polymerization, the monomer in oil system employs less surfactant, the 
process is less energy intensive, and solvents can be recycled.
Two different kinds of crosslinkers were introduced to prepare the microgel. One 
reagent was considered to be thermally and hydrolytically stable. A second was 
considered thermally labile, which could be broken under the stimuli of raised 
temperature in an aqueous environment. The gel particles initially absorb water and 
swell upon dispersion in water. When the labile crosslinked particles in water were 
heated, the microgel further expanded under constraint of the remaining crosslinker.
Pore occlusion efficiency by dispersions of swollen PAM microgels was 
evaluated by a nuclear-pore film filtration model system. Traditional evaluation 
methods,
24,28,29
such as core-flooding test, can show the overall information of oil 

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recovery efficiency. Whereas, the membrane filtration system is designed to investigate 
how microspheres plugged the nuclear-pores and their plugging properties
22,30
. In this 
paper, the matching behavior between the size of microgel particles and pores and the 
pitch of pores as well as the plugging performance of those microgel particles were 
studied.