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Porous silica materials offer wide range of possibilities for enhancement ofthe productivity of oil reservoirs. However the mechanism of adsorption ofpolar components of crude oil on silica surface is poorly understood thathinders technological improvement of supports and oil extraction. We havesynthesized opal films with the silica microspheres size of about 360 nm,specific surface area of 5.2 m2/g and pore size of 230 nm. We have fractionatedand characterized oil and oil asphaltenes from heavy (Ashalchinskoe) oil. Bypulsed electron paramagnetic resonance (EPR) and double electron nuclearresonance (ENDOR) in the W band frequency range (microwave frequency of 94 GHz,magnetic field of 3.4 T) we have studied the adsorption of oil asphaltenes onthe surface of opal samples using the intrinsic for asphaltenes paramagneticvanadylporphyrins (VO) complexes. 1H ENDOR spectra are found to be differentfor initial and the adsorbed samples in their central parts (that is a sign ofasphaltenes VO disaggregation) whereas no significant changes in the W band EPRspectra were detected. Contrasting to alumina support, no strong electronproton interaction with the protons on the surface of SiO2 (presumably, silanolgroups) was found and infiltration of the oiled opal films with gasolinechanges the central part of 1H ENDOR spectra. It shows that the protoncontaining groups on the surface of amorphous SiO2 sample can significantlychange the asphaltene adsorption properties and ENDOR of the intrinsic for oilparamagnetic centers could be used for the characterization of surface state inporous media in situ or operando.

Probing the surface of synthetic opals with the vanadyl-containing crude oil by using EPR and ENDOR techniques