Experimental investigation on transport property and emulsification mechanism of polymeric surfactants in porous media

Abstract

Polymeric surfactants display different capabilities in migration rules and emulsifying crude oil as compared with that of traditional polymers attributing to the co-existence of hydrophilic and hydrophobic groups in molecular chains. To investigate the migration rules of polymeric surfactants in porous media and the matching relationship between polymeric surfactants and porous media, seepage-behavior experiments of different concentrations of polymeric surfactants in different permeability and different length cores were first carried out. The generation of emulsified oil droplets with the polymeric surfactants was then elucidated by comparing core flooding experiments with different injection rates, different saturated oil types and different polymeric surfactants concentrations. The flow characteristics of the emulsion and displacement mechanisms were evaluated by microscopic displacement experiments. The results showed that unlike polymers, when the polymeric surfactant was transported in porous medium, the pressure was difficult to reach a stable state. Based on the matching coefficient, the migration rules of polymeric surfactants in porous media could be defined as high blocking weak flow mode (λ < 14.7), a blocking flow equalization mode (14.7<λ < 19.7) and a smooth flow mode (λ > 19.7). The main reasons for the formation of polymeric surfactants emulsions are a certain shearing action, the snapping action of hydrophobic microdomains on residual oil droplets and assisted effect of colloidal asphaltene. Capillary number(Nc) was used as an evaluation index to divide the emulsification action into four zones: non-emulsified zone(Nc < 2.18 × 10−5), high-efficiency emulsification zone (2.18 × 10−5<Nc < 8.7 × 10−5), optimal-emulsification zone (8.7 × 10−5<Nc < 1.46 × 10−4) and emulsified excess zone(Nc > 1.46 × 10−4). The emulsion microscopic flooding experiment showed that in the porous medium, the transport characteristics of polymeric surfactants emulsion were mainly plugging action of single large emulsion particle, stacking and plugging action of small emulsion particles, forming “emulsion bridge” to block super large pores and vortex action of different sizes emulsion particles.