Someone (Saudi Arabia and US) has been leaning on the 'produce the f@ck out of oil' button for a long time now and it has sent oil prices plummeting. I believe this is essentially a price war with the aim to put Russia (and incidentally ISIS) out of business (again).
Yes, this harms the growing US energy industry, but the net benefit of lower oil prices plus maintaining hegemony is positive for the US economy. Plus, the US isn't financing government budgets using energy exports. Russia, on the other hand, is the world's largest energy exporter and is HEAVILY dependent on energy revenues. Nowhere is the effect of lower oil prices on Russia's economy more evident than in the following chart showing Russia's plummeting FX and gold reserves, which not coincidentally mirrors a similar decline in the Ruble: