Stability of PAM/PEI emulsified gels under HTHS conditions for water shut-off treatment

Emulsification has been widely used in the oil industry. The thermal stability of emulsified systems, such as emulsified gels or acids, is critical for the placement success of the emulsified system. Early separation of the system in a tubular well leads to corrosion. In the present study, the stability of emulsified polyacrylamide/polyethylenimine (PAM/PEI) gels is investigated in high-temperature and high-salinity (HTHS) environments. The influences of different parameters such as surfactant concentration, water–oil ratio, salinity, intensity of mixing and temperature on the droplet size and the emulsion thermal stability are studied. The droplet size of the PAM/PEI system, which is emulsified in diesel, decreases, and the separation time increases with increasing mixing speed, surfactant concentration, and salinity. The emulsions with smaller droplets are thermally stable compared with large droplets since the rate of droplet coalescence is low. The effect of emulsion stability on gelation kinetics and gel strength is investigated. The emulsification reduces both the gel strength and the gelation rate. The cross-linking (gelation) rate in the unemulsified PAM/PEI is almost ten times higher than that in the emulsified gels. This gelation process is slow in the case of stable emulsified PAM/PEI solution and is believed to be the result of limited heat and mass transfer. The emulsion stability achieved in this work adds to the current understanding of how to control emulsion stability through different parameters to withstand HTHS environments and how this stability influences the gelation process.