I am a Ph.D student currently interested in fluid flow in porous media (rocks in my case). I am currently trying to find the range of values for the contact angle in air-water-sandstone systems at shallow reservoir conditions (say 7.5MPa and 35 degrees C). The only value I have managed to come across is 0 degree. Most papers out there seem to assume zero degree, although no reason for this assumption is given. I was wondering if any of you had any idea as to why such assumption is made and when is it valid ? My understanding is that the assumption is made to represent complete wetting of the rock by the water. If that is the case wouldn't that change as more and more air is injected in the rock ?