Asphaltenes are indigenous species in crude oil responsible for formation of tight crude oil-water emulsion during oil recovery. It is important to understand interfacial behavior of asphaltenes at the oil-water interface to understand the oil recovery process. In recent studies, using pendant drop as Langmuir trough and interfacial rheology measurements, it was concluded that asphaltenes follow a Langmuir equation of state (EOS). Such a Langmuir EOS involves only one parameter, namely surface excess coverage, which is actually the size of the molecule at the interface.

This study discusses creation of asphaltene stabilized interfaces from four crude oils from the Monterey shale and extracted asphaltene powder. Interfacial rheology and pendant drop measurements were conducted and it can be observed that the Langmuir EOS is followed for all four oils and extracted asphaltenes. The size of molecule at the interface is approximately 0.36 nm2 for all crude oils and 0.34 nm2 for extracted asphaltenes, respectively, which is consistent with the well-known Yen Mullins model. It confirms that crude oil-water interfaces are predominantly stabilized by asphaltene molecules present in crude oil.

Asphaltene stabilized interfaces are exposed to the weakly emulsifying (WE) and non-emulsifying (NE) surfactant families, which have been widely used during matrix acidizing operations in the Monterey shale. Interfacial rheology measurements conclude that asphaltene stabilized interfaces are elastic. Elastic interfaces are almost immobile (solid-like) and hence, during oil recovery, can cause issues while flowing through porous media. WE surfactants, as studied previously, form a weak emulsion during oil recovery, which aids more recovery 13 . WE surfactants also reduce the elastic modulus of the interface significantly within seconds to make the interface mobile and deformable. Hence, it helps the oil droplet mobilize, squeeze, or elongate through the pores during oil recovery. NE surfactants, on the contrary, reduce elastic modulus slowly and do not appear to reduce the elastic modulus enough to make interface deformable (still remains elastic).

Corresponding field data shows that wells treated with WE surfactants show higher oil recovery consistently than those wells treated with NE surfactants.

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