My deduction is based on the name they chose to represent the federation of the 2 self-proclaimed republics, Donetsk and Lugansk, "Nuovorussia", and on the way the "conflict" evolved.
The interest of Russia here is very obvious. Even if the conflict was started by the separatists or the whole thing is a trick performed by Putin, if we will get to see the emerging of a new state/federation in the north of the Black Sea, it will not be for too long. Most of, if not all, of the separatists are "in love" with Russia. The probability that they will not only unite with Russia, but even let them be anexed by Russia(in order to improve russian image), is impossible to ignore.
So Putin's logic is about like that: NATO tries to get to my border? It is unavoidable, as it would have happened sooner or later. Then let's prepare ourselfes and make them a surprise by being us the firsts to get to their border(Nuovorussia's de jure spreads in vest to Romania and Moldova Republic). The new ressources and positioning would be a bonus and a tool. Evrika!