Thermal and Rheological Study on Polyacrylamide Hydrogel Polymers for Water Shutoff Application

Abstract Hydrogel polymers have gained an increase in demand as plugging material in water control and loss circulation applications due to their effective expansion properties. The increased demand can be explained by the fact that this technology does not require high investment in chemicals and equipment. Hydrogel is a polyacrylamide polymer which are effective in plugging due to the presence of carboxylate groups that enables crosslinking. Though, thermal and mechanical properties of polyacrylamide polymers are subjected to syneresis, precipitation, and breakage at field conditions and interaction. Thereby, this study focuses on developing an understanding of hydrogel polymer behavior when subjected to different conditions. In this study, an extensive laboratory work was conducted to explore potential intrusion of cations in formation water with carboxylate groups in polymer structures. 100 ml of brines of KCl, NaCl, CaCl2 and MgCl2 at concentrations of 1, 2.5 and 5.5 wt% were used to investigate a subjected polyacrylamide hydrogel polymer swelling with time. Rheological measurements were conducted between 60 and 90°C after hydrolysis of the polyacrylamide polymers. A complete simulation of water shut off treatment was conducted using a linear-based core flooding system that enables studying rock/gel interaction. Different fracture shapes were also made inside tested carbonate core plugs to test subjected hydrogel polymer in reducing infinite permeability. The results showed that the positive charges of cations in formation water reduced polymers swelling fraction significantly. One gram of the polymer absorbed 100 ml of deionized water in 30 minutes while 54 ml was absorbed from a 1 wt% KCl brine in 90 minutes. This negative effect was more significant when divalent ions existed in solution as only 20 ml of the 1 wt% CaCl2 brine was absorbed in 90 minutes by 1 gram of the polymer comparing to 54 ml from the 1 wt% KCl brine. Rheological tests showed that pH manipulation can be used to facilitate polymer pumping where solution viscosity at pH of 1 was 16 cP and at pH of 7 was 575 cP at 60°C. The simulation model showed that pumping hydrogel polymer at low pH reflected a low pumping pressure. However, once the polymer was in contact with carbonate rock, solution's pH raised and hydrogel polymers enlarged significantly and plugged the created fracture along with surrounded matrix permeability which reduced the overall core permeability by more than 95%. Successful placement and implementation of water shut off treatment can be achieved by promoting the functional properties of hydrogel polymers. Therefore, optimization of polyacrylamide hydrogel polymers can be achieved by understanding how surrounded conditions can be altered and manipulated.

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