High-molecular-weight polyacrylamide
(PAM) has been widely used
in chemically enhanced oil recovery (EOR) processes under mild conditions,
but its poor tolerance to high temperature and high salinity impeded
the use in severe oil reservoirs. To overcome the inadequacies of
PAM, thermoviscosifying polymers (TVPs) whose viscosity increases
upon increasing temperature and salinity were developed in recent
years. In this work, comparative studies with PAM and TVP, having
more similar molecular weights, were performed with regard to their
rheological behaviors, thermal stability, and core flooding feasibility.
It was found that the TVP aqueous solution exhibited thermothickening
ability, even at a polymer concentration of 0.2 wt % with a
total dissolved solids ratio (TDS) of 101 000 mg L–1 upon increasing temperature, while PAM only showed a monotonic decrease
in viscosity under identical conditions. Remaining viscosity of TVP
was higher than that of PAM after aging at 45 or 85 °C for one
month. Core flooding tests demonstrated both polymers show good transportation
in porous media, and a higher oil recovery of 16.4% and 15.5% can
be attained by TVP at 45 and 85 °C, respectively, while those
of PAM are only 12.0% and 9.20%.
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