Water shutoff agent of PEI gel applicable to high temperature and high salinity reservoirs

A gel type shutoff agent with anionic polyacrylamide as a main agent required for high temperature and high salinity formation water shutoff was developed using a crosslinking agent of water soluble polymer-polyethylenimine (PEI), and protective agent was added to slow down hydrolysis of the main agent under high temperature. The impact of main agent mass fraction, main agent molecular weight, PEI mass fraction, PEI molecular weight, salinity and pH was experimentally investigated on gelling performance of PEI gel. Experimental results show that the relative molecular weights of main agent and PEI increase as the mass fraction of main agent and PEI increases while the gelation time is shortened. But under high mass fraction, excessive crosslinking is more likely to occur, causing premature gel dehydration. The gelation time is shortened with the increase of pH values, and becomes longer with the increase of salinity. At 110 ℃, for formation water with NaCl content of 50 000 mg / L, the gel shows high strength and good resistance to temperature and good blocking effectiveness, and remains hydrated for at least 120 days. The optimum formula for water shutoff system is 0.6% to 0.8% anionic polyacrylamide 0.3% to 0.7% PEI 0.8% to 1% high temperature protective agent.