Polyacrylamide and its derivatives for oil recovery

3. Cross-linked Polymer Used in Gel Treatment 
Excess water production is a frequent problem occurs in mature reservoirs owing 
to long term water flooding. It can cause multiple concern in environment, exacerbating 
the levels of corrosion and scale.[172] Gel treatment normally is one of the best option 
for this problem.[173-175] Crosslinking polymers have been widely applied to correct 
reservoir heterogeneity and improve the sweep efficiency of displacing fluids (normally, 
water.) Gel injection can reduce flow capacity fractures and divert following fluid. The 
polymers mentioned in polymer flooding part have employed various cross-linkers to 
form gels. A polymer gel is a 3D network and can be used to obstruct higher permeability 
zones/streaks/channels in reservoirs so that the flowing water can enter oil-riched non-
swept zones/areas to displace more oil from the formation pores.[176-184] There are 
many reactive inorganic and organic “functional” groups that can provide crosslinking in 
HPAM polymers, such as –COO
-
, -CONH
2
, and -COOH. Cross-linkers can also be 
introduced into HPAM by co-polymerizations with AM monomer. There are essentially 
three types of crosslinking structures employed in EOR, associative crosslinking by ionic 
bonds, associative crosslinking by a chelation effect, and direct crosslinking by covalent 
bonding.[185]

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39 
Polyacrylamide per-se is electrically neutral and comprises a saturated 
hydrocarbon (C-C) backbone with amide side chain groups. When subjected to aqueous 
alkalinity or elevated temperatures, some of the amide groups in PAM are converted to 
carboxylate groups where the degree of hydrolysis typically varies from 0 to 50%[15, 
186, 187] The formed anionic charges can develop ionic bonding arrangement in the 
presence of multivalent cations[188-191] (valence state), such as B(III), Cr(III), Al(III), 
Zr(IV), Fe(III), or Ti(IV). Through the interaction between –COO 
–
in PAM and one, or 
more, multivalent inorganic cations, a 3-dimensionalnetwork structure of the PAM 
polymers (see Figure 8) is achieved.[161, 192-197] Cross-linkers of this kind are 
inorganic, formal ionic salts but can be reduced in their effectiveness of solution viscosity 
control by the presence of monovalent captions such as sodium or potassium, which 
compete for anion association sites.
C
O
O
-
C
O
O
-
C
O
O
-
Cr
3+
PAM chain
PAM chain
C
O
O
-
C
O
O
-
C
O
O
-
Cr
3+