Effects of molecular structure of polymeric surfactant on its physico-chemical properties, percolation and enhanced oil recovery

Abstract Polymeric surfactant can simultaneously thicken aquous phase and reduce water–oil interfacial tension (IFT), which makes it present a great application prospect in the oilfield taword enhanced oil recovery (EOR). There are two kinds of polymeric surfactant with different molecular structures are commonly used to realize the salt resistance, thermal endurance and shear resistance. However, the influence of the molecular structure of polymeric surfactant on their properties related on EOR are not well understood. In the work, we synthesized two kinds of polymeric surfactants with different molecular structure which respectively named intermolecular association molecule (IAM) and rigid chain molecule (RCM). Their physico-chemical properties, porous media transportation and EOR are compared with a series of experiments. It is found that the hydrodynamic characteristic sizes and retention of IAM are higher than those of RCM via the membrane filtration test and nuclear magnetic resonance (NMR) scan. These features make IAM have a larger resistance factor and residual resistance factor than RCM and hydrolyzed polyacrylamide (HPAM) in the same viscosity. Compare to HPAM with shear thinning, RCM presents a Newtonian fluid region and IAM presents a shear thickening region when the shear rate is lower than 1 s−1. The spatial structure of IAM can pack oil drop into its network, which make it easy to form oil-in-water-in-oil (O/W/O) emulsions. Moreover, the concentration and water–oil ratio (WOR) rarely affect the stability of IAM emulsions once the intermolecular association generated. The increamental oil recovery factor of IAM is 17.5% after water flooding in the three-layer core flooding experiments with the permeability of 500 mD, 1500 mD and 3000 mD at 55℃, which is higher than that of 14.5% for RCM and 11.4% for HPAM.