Polyacrylamide and its derivatives for oil recovery

3.3
 
 Polyacrylamide Micro-gels/Micro-spheres 
PAM micro-gels are, in general, also cross-linked by organic cross-linkers. 
Micro-gels are special colloidal gel particles or polymers, which have been shown to be 
able to change their gel configuration in response to external stimuli.[290] Unlike macro-
gels, micro-gel or sub-micro-gels have been designed to activate certain properties at a 
pre-determined “in-depth” location within in the reservoir (see Figure 13). For instance, 
micro-gel systems typically contain expandable polymeric particles possessing both 
labile and stable cross-linkers. Under the stimuli of pH or temperature extremes, the 
labile cross-linker will degrade to decrease the degree of crosslinking where the 
polymeric particles can expand to many times their original volumnar size (see Figure 
14), which can block pore throats and direct injection water into unswept oil-rich zones. 
Inverse-emulsion, micro-emulsion, suspension, and precipitation polymerization methods 
are the most common approaches to establish control the particle sizes within a narrow 
range, from milli- to nanometer size scales.

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Figure 13. 
Illustration of the fundamental difference between macro-gels and micro-
gels. [291]
Figure 14. 
Proposed swelling mechanism of an expandable polymer particle.
 
An example of a micro-gel joint research and development by an industry 
consortium (BP, Chevron Texaco, and Nalco Company) was called the Bright Water 
project. The micro-gel product has been in practical application since 2001 and has been 
applied in about 60 wells. In preparation of the product, the initial polymeric “kernel” 
particles sizes of 0.1 to 3 um were first synthesized through an inverse emulsion 
polymerization process.[292-296] Through esterification between carboxylic and 
hydroxyl groups under an azeotropic, thin film evaporation technique to remove water, 

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the polymeric micro particles were internally cross-linked with labile cros-slinker. Upon 
adding light mineral oil, surfactants, brine, and completely mixing, a dispersed kernel