I would like your help to suggest for me a good solution, commercially available, apart from oil to change the core sample wettability from hydrophilic to hydrophobic.
add a surfactant of opposite charge to the surface which you are trying to change. Do not add too much either approx half the cmc would be best to try first, if you add too much rather than a mono-layer adsorbing a bi-layer will form which is hydrophilic again