The conventional experimental techniques used for performance evaluation of enhanced oil recovery (EOR) chemicals, such as polymers and surfactants, have been mostly limited to bulk viscosity, phase behavior/interfacial tension, and thermal stability measurements. Furthermore, fundamental studies exploring the different microscale interactions instigated by the EOR chemicals at the crude oil-water interface are scanty. The objective of this experimental study is to fill this existing knowledge gap and deliver an important understanding on underlying interfacial sciences and their potential implications for oil recovery in chemical EOR.

Different microscale interactions of EOR chemicals, at crude oil-water interface, were studied by using a suite of experimental techniques including interfacial shear rheometer, Langmuir trough, and coalescence time measurement apparatus at both ambient (23°C) and elevated (70°C) temperatures. The reservoir crude oil and high salinity injection water (57,000 ppm TDS) were used. Two chemicals, a nonionic surfactant (at 1000 ppm) and a sulfonated polyacrylamide polymer (at 500 ppm and 700 ppm), were chosen since they are tolerant to high salinity and high temperature conditions. Interfacial viscous and elastic moduli (viscoelasticity), interface pressures, interface compression energies, and coalescence time between crude oil droplets are the major experimental data measured.

Interfacial shear rheology results showed that surfactant favorably reduced the viscoelasticity of crude oil-water interface by decreasing both elastic and viscous modulus to soften the interfacial film. Polymer in brine either alone or together with surfactant increased viscous and elastic modulus at the oil-water interface thereby contributing to interfacial film rigidity. Interfacial pressures with polymer remained almost in the same order of magnitude as the high salinity brine. In contrast, a significant reduction in interfacial pressures with surfactant was observed. The interface compression energies indicated the same trend and were reduced by about two orders of magnitude when surfactant is added to the brine. The surfactant was also able to retain similar interface behavior under compression even in the presence of polymer. The coalescence times between crude oil droplets were increased by polymer whereas substantially decreased by the surfactant. These consistent findings from different experimental techniques demonstrated the adverse interactions of polymer at crude oil-water interface to result in more rigid films, while confirming the high efficiency of surfactant to soften the interfacial film, promote the oil droplets coalescence and mobilize substantial amounts of residual oil in chemical EOR.

This experimental study, for the first time, characterized the microscale interactions of surfactant/polymer chemicals at crude-oil water interface. The applicability of several interfacial experimental techniques has been demonstrated to successfully understand underlying interfacial sciences and oil mobilization mechanisms in chemical EOR. These techniques and methods can provide potential means to efficiently screen and optimize EOR chemical formulations for better oil recovery in both sandstone and carbonate reservoirs.

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