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(20): p. 7762-7771.
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SECTION
3. CONCLUSION
This dissertation has discussed the synthesis, characterization and application of
polyacrylamides and polyacrylamide hydrogels.
Paper I mainly reviewed the function of polyacrylamide and its derivative
products in EOR through two main aspects: one is the viscosity thickener as the polymer
flooding agent; another is they can act as sealing agent via forming cross-linking
structure in present of cross-linkers to render conformance control. This review clearly
indicates the structure of the different polyacrylamide and their derivatives as well as the
according properties of them. In particular, this review elaborates synthesis methods of
each kind polymer and gives their application in detailed.
For the polyacrylamides working as the displacing agent, they work as a basic
thickening agent in polymer flooding solution. As the reservoir environment turning
harsher and harsher, a plenty of modification methods came up aiming at conquering the
high temperature, high salinity, and harsh pH envrionment. Typically functional
monomers have been summarized that could be employed to modify the polyacrylamide
chain hence increase the solution viscosity facing different reservoir.
From the point of different crosslinking types, PAM hydrogels were reviewed
aiming at the gel synthesis, mechanism of crosslinking, performance, lab evaluation and
practical applications. This work will benefit A number of crosslinkers were summarized
according to their type, properties and working conditions.
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This paper mainly reviewed the PAMs based polymers and hydrogels utilized in
EOR, highlighting the synthesis methodologies, structure and properties of the products
as well as their real application in oil field, aiming at drawing more attention of chemists
to this surging area of interest so that more advanced products could be developed to
meet the tremendous demands for oil industry. In addition, polymers for EOR have been
intensively applied in China and a lot of publications are in Chinese, and this paper will
also benefit those who are not familiar with Chinese language.
In Paper II, a water-free, solvent-in-oil emulsion polymerization has been
developed to synthesize polyacrylamides. The preparation of polyacrylamides has been
conducted above the melting point of monomers in non-polar solvents. A number of
surfactants had been studied in stabilizing this water-free system. Compared to traditional
inverse emulsion polymerization, the water-free solvent in oil method consumed much
less surfactant. Alkylacrylamides were employed as sufmer to stabilize the emulsion
system as a surfactant and also polymerized into copolymer to introduce hydrophobic
domain forming hydrophibically modified polyacrylamides. By virtue of this technique,
the feed ratio of the hydrophobe will not be limited as it is in a traditional aqueous
polymerization system. Products are dry powder and ready to use disperse in water,
compared to traditional synthesis that require post-treatments, like drying, which
increases energy cost. Additionally, dry powders are stable and easier to store and
transport than wet polymer solution.
In Paper III, polyacrylamides microgel was synthesized by water-free, solvent-in-
oil emulsion polymerization. Two different crosslinkers were employed to give the
synthesized particles ‘smart’ properties with two stages of size expansion that are
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temperature sensitive. Original diameter of the microspheres was under 10µm. After fully
swelled in water under room temperature, the microgel’s diameter had swelled to less
than 20 times as the original size. While under higher temperature stimuli, the average
volume of the saturated microgels swelled to over 150 larger than the original volume.
High temperature could trigger the cleavage of labile crosslinker and some of the stable
crosslinker. During the whole process, the shape of the microgel particles remained
spherical. Plugging performance of the microgels was studied. There is a certain
matching relationship between the microgel particle size and the pore size as well as the
porosity. If the size of gel particles is much larger than the pore size, they will not
produce effective occlusion due to steric hindrance. Swollen microgels sealed the nuclear
pores with effective plugging, when size matched.
Paper IV described PAM / PVA inter penetrating network hydrogels, which
showed much higher mechanical strength compared to pure PAM network and could be
applied in gel treatment under harsh environment. IPN hydrogels were produced by
crosslinking PAM-MBAM and PVA-glutaraldehyde at the same time in one aqueous
system. Flory-Rhener theory was used to study the effect of loading of PVA on the
swelling and mechanical properties of IPN hydrogel. It is shown that the IPN hydrogel
matrix fabricated may easily be tuned in terms important parameters such as mechanical
strength, swelling and porosity as per need by varying composition, thus fulfilling
specific application requirements. PAM/PVA IPN hydrogels as plugging agent for gel
treatment has been studied by evaluating hydrogels swelling properties in brine, under
stimuli of pH changing and salt concentration. The PAM/PVA IPNs showed less
sensitivity to salt and pH change than pure PAM hydrogel, which is preferred in EOR.
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Both PAM and PVA are bio-compatible material, and meanwhile the PAM/PVA IPN
hydrogels are of highly porous structure, which will be suitable for potential tissue
engineering and biomedical applications.
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