This is mentioned in a report from the Russian defense ministry here.
They stated that out of 70 drones, 25 were allegedly shot down over the Volgograd region. Its governor, Andrey Bocharov, reported that due to the supposed debris from the drones, local fires broke out at the oil refinery. Additionally, there were power outages in certain areas of Volgograd.
It is likely that the drones targeted the Lukoil oil refinery. Notably, on January 31, it was already under attack from Ukrainian drones.
Explosions were also heard in Astrakhan. As reported by the head of the Center for Countering Disinformation of the National Security and Defense Council, Andrey Kovalenko, drones hit the Astrakhan gas processing plant — one of the key Russian enterprises responsible for processing gas condensate and producing gasoline and diesel fuel.
The governor of Astrakhan region, Ilya Babushkin, stated that the drones attempted to attack fuel and energy sector facilities, and a fire occurred when one of the UAVs fell.