According to Elliotte Friedman, the Oilers are interested in all three of Noah Hanifin, Chris Tanev, and/or Nikita Zadorov. The asking price won't be small so any team interested in these players will have to dig deep into their pockets.
All three of these defensemen are pending unrestricted free agents so there are a lot of options to go about this for the Flames. It seems right now that their season is on the rocks and they might try to trade these players while their values are high, but it's also possible they want to stick it out for the year and see what happens in free agency.