In the first six months of 2023, total budget expenditure rose to almost 15 trillion rubles (€142.3 billion), an increase of 2.5 trillion rubles (€23.7 billion) on the previous year, with defence spending responsible for almost the entire difference, economic analyst Boris Grozovsky says. The Russian government has simultaneously increased military spending while decreasing spending in other sectors, which is “why budget statistics are no longer being released,” Grozovsky added.
https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=MCSSTUS1&f=M
According to this, since February 2022, when the invasion started, it’s fallen by 40%. That’s significant, but not exactly running dry at this point.
Not to mention that’s just the strategic reserves. Thanks to shale fracking, the US is the largest petroleum producing country in the world, and that isn’t likely to change any time soon.