Research on the Gelation Performance of Low Toxic PEI Cross-Linking PHPAM Gel Systems as Water Shutoff Agents in Low Temperature Reservoirs

Using gel as the water shutoff agent has been widely reported in the aspect of enhanced oil recovery (EOR) of the development of mature oil fields. Cross-linkers such as chromium(III) acetate and phenol formaldehyde are commonly used, but they are toxic. Today, use of low toxic polyethyleneimine (PEI) cross-linking a copolymer of acrylamide and tert-butyl acrylate (PAtBA) as the water shutoff gel is reported more but is mainly focused on its theoretical research and applications in high temperature reservoirs. Because of the defects of the chromium(III) acetate and phenol formaldehyde cross-linkers, the gelation performance of PEI/partially hydrolyzed polyacrylamide (PHPAM) gel systems at low temperature (40 degrees C) is discussed in this paper. The results show that the gelation time and strength of the PEI/PHPAM gel system can be perfectly controlled by adjusting the PHPAM concentration, the molecular weight, the PEI concentration, and the total dissolved solids. The polymer concentration and molecular weight can affect not only the gelation time and the gel strength but also its stability. Among them the polymer concentration is the most important factor that affects the gel stability. For the low temperature reservoirs, the most common used chromium(111) acetate/PHPAM gel system has only around 5 h of gelation time at 40 degrees C to get a high gel strength. However, the PEUPHPAM gel system can achieve a much longer gelation time. Polymer gels formulated with a combination of 1.5 wt % PHPAM and added 0.3-0.8 wt % PEI provide a gelation time between 15 h and 9 days, and the maximum gel strength could reach code I. This study suggests that the low toxic PEI/PHPAM gel system can be used in low temperature reservoirs.