Polyacrylamide and its derivatives for oil recovery

Keywords 
Poly (vinyl alcohol), Polyacrylamide, Inter-penetrating network, Swelling kinetics, 
Rheology, Mechanical Properties 
Introduction 
Hydrogels feature a three dimensional polymer network structure that can absorb, 
swell and retain aqueous solutions up to hundred times their original weight and 
volume.[1, 2]
Generally, they are water soluble polymers loosely crosslinked by ionic, 
organic crosslinkers and/or physical crosslinking points to form three dimensional 
network structures. Hydrogel properties such as mechanical [3], thermal, optical,[4, 5] 
electrical,[6, 7] and responsiveness [8, 9] behaviors can be tunable by adjusting 
composition and crosslinking density. These properties enable hydrogels for a variety of 
applications in: flocculents or scavenging agents,[10, 11] drug delivery agents,[12-14] 
bio-compatible tissues,[15, 16] sensors,[9, 17, 18] oil recovery [19-21] and other 

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areas.[22] Polyacrylamide (PAM) hydrogels are one of the most important hydrogels 
used in these areas. 
In enhancing oil recovery (EOR) applications, PAM hydrogels have become a 
commonly utilized plugging agent/diverting agent toward conformance control, which is 
ascribed to their relatively low cost, non-toxicity and biological inertness, long polymer 
chain length and high molecular mass, stability of mechanical and morphological 
properties, and ability to customize their properties.[23, 24] Bai et al. has researched [21, 
25-28] polyacrylamide preformed particle gels (PPG). Lab and field experimental results 
support use of PPG treatments as cost-effective methods for treating permeability and 
flow heterogeneity issues in petroleum reservoirs with fractures or void space channels, 
each of which are widely found in mature water-flooded oil fields.[19, 29]
Under stimuli of acid or salinity, on the one hand, PAM hydrogels display 
dramatic shrinkage in size due to ion shielding effects.[30, 31] On the other hand, highly 
swollen PAM hydrogels are generally brittle since they are lack of an efficient energy 
dissipation mechanism arising from an irregular distribution of crosslinking points.[32, 
33] These drawbacks have limited PAM hydrogels’ applications under some 
circumstances. Improving the mechanical properties of PAM hydrogels is one potential 
means to expand their application. Compared to PAM gels, PVA hydrogels are another, 
inexpensive material which has low toxicity, good bio-compatibility[34] but lower 
hydrophilicity. Most importantly, PVA has better resistance to pH-changes, salinity, 
temperature and higher mechanical strength capability. When incorporated into other 
polymer hydrogels, PVA has the capability to improve their mechanical properties [35] 
as an environmentally friendly modifier. PVA has been incorporated into PAM hydrogels 

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to make PAM/PVA composition, and achieved improvements in acid and salt- resistance 
as well as mechanical strength, demonstrating that PVA hydrogels can function well in 
harsh acidic or briny environments.[36-38]
Two methods have been reported to incorporate PVA into hydrogel polymer 
networks: (1) Polymerizing or crosslinking water soluble monomers or polymers in PVA 
solution.[39, 40] In this method, water soluble monomers or polymers and their 
crosslinker were dissolved in linear PVA solution and an in-situ polymerization and 
crosslinking reaction results after adding initiator. The synthesis is a physical mixing 
initially that, through polymerizing and crosslinking acrylamide, incorporates linear PVA 
into a gel matrix[41] without further crosslinking as semi-interpenetrating networks or 
semi-IPN.[42] (2) Polymerizing or crosslinking water soluble monomers or polymers in 
PVA solution, following by a freeze-thaw associative crosslinking of PVA.[43, 44] 
Compared to the first network example, the freeze thaw method provided a second 
network via creating hydrogen bonds as associative crosslinking points between PVA 
polymer chains. The associative IPN was stable in moderate temperature or shear 
environments due to disruption of hydrogen bonding under elevated temperature 
(45~55 ͦC) or shear.[45, 46] When these stimuli are applied, the associative crosslinking 
points may dissociate to form a semi-IPN. For semi-IPN PVA could be released into the 
environmental aqueous solution. 
In this experimental study, a series of PVA/PAM IPN hydrogels containing 
various amounts of PVA were prepared by in situ free radical solution polymerization of 
AM and MBAM, as well as a chemical crosslinking of PVA by glutaraldehyde [47,48]. 
Production of the IPN versus a semi-IPN entanglement[41] or associative hydrogen 

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bonding crosslink, by covalent bonding between PVA polymer chains should provide a 
more stable network under aqueous swelling and shear. An IPN of PAM and PVA is 
intended to improve the mechanical properties of the swollen three dimensional IPN.
The swelling performance of the hydrogels as a function of salt concentration and 
different pH were measured. Rheological and mechanical properties are determined and 
discussed.