The vast majority of Russia's economic growth is coming from oil and gas reserves, especially the latter. That's a notoriously shaky ground on which to build an economic expansion as rapid as Russia's has been in the last few years. Extremely volatile over the long run. It doesn't help that most of that wealth is being captured by a handful of government-sanctioned plutocrats, and by government officials themselves (Putin most especially; he is rumored to have a personal net worth in excess of $70 billion). A very small proportion is actually being reinvested into productive and petrochemical-diverse industry. To make matters worse, the country suffers from some major demography issues. Its birthrate is problematic, and its population is old. It is one of the few major industrialized nations whose population is expected to contract significantly over the next century.
There is very little stability underpinning Russia's economy. It's wobbly, as is, right now. It'll be wobblier still over the next 10-20 years.
