Ukrainians distrouyed Kremlin plans on marginalizing Ukraine's energy cooperation and reverse gas supply from the EU and forcing international companies to leave Ukraine.

Invasion into Ukraine and annexation of Crimea putted on hold offshore projects in the Black Sea. Pirate capture of Chernomornaftogas assets threatens to damage most of Ukraine's production fields and rigs even in the best scenario.

Russia tries to convert Black sea region into the area of instability to eliminate and block delivery of Caspian energy to Europe. Its plans might spread from wider control over Black sea coast and until full chaos in the Black sea to make unpossible tanket traffic. 

The main reason is to force oil prices up, as the fall will mean fate of Soviet union for Russia.