On the other hand, the people at Shell are buying up those water rights for a reason...

Might it have something to do with declaring the shale leases as some potential class of reserves?

My thought exactly. There is no way there can be enough water to scale up this operation enough to be profitable. I can see a small scale "experimental" operation but that is it.

Spare water reserves in the Colorado basin generally end up in the faucets of Los Angeles. Thats the 2.5 million people that need the water.

The other thing that occurs to me is Shell is going to have great earnings. The folks managing those earnings (trying to deflate them for instance), might wish to sequester some money in a safe place. Those water rights are probably the best investment that's arguably energy related (therefore an expense) they can make.