Professor Dave Prior
One of the limitations you are always up against in trying to look at rocks is that we always look at two-dimensional sections, and in reality, of course, rocks are three-dimensional things, and some of the properties of them are highly dependent upon how things fit together in three dimensions. So the flow of fluids like water through a rock is a really important control on how they behave, and you can’t really understand the ability of fluid to flow through a rock without thinking in three dimensions. One of the places you get water in the rock are in pore spaces, basically holes in a rock, and if those holes are connected up, it’s permeable. If they’re not connected up, the water can’t get through. And if you imagine you have your permeability as long thin tubes, and you cut it one way, and you’ll see sections, which are like long thin things, and you think, “Oh, that’s nice and permeable.” If you cut it at 90 degrees to that, you’ll see a whole load of circles, which aren’t connected to each other and you’ll think, “Well that doesn't look very permeable.” And you don’t really get the answer unless you can put those together and see the thing in three dimensions. Now there are all sorts of variants of three-dimensional scanning which has come from innovations in medicine, which enable us to map out in three dimensions the density distribution in a rock. So looking for the three-dimensional arrangement of pore spaces is something that CT-type methods are very good for.
Professor David Prior, Dr Virginia Toy, Andrew McNaughton and Hannah Scott, University of Otago.
Rock pore diagrams, courtesy of CO2CRC.
3D animation of micro CT sample, by Hannah Scott, University of Otago.