This post in a LinkedIn group that I follow, linking to this article, got me thinking a bit about wettability. I was struck by the comment that “conventional wisdom says that clays are always water-wet”. The article makes good use of pretty advanced analysis and imaging technologies to show that this is not (always) the case. We can show evidence for similar effects using the rather more mundane thin-section petrography, and can add that we very commonly see illite-cements, in particular, that are very heavily oil stained (implying some degree of hydrocarbon wettability) while other mineral surfaces are oil-free.
