It's hard to tell if the US sanctions are really a serious attempt to do anything. They don't seem to matter at all to Exxon who is moving forward to provide drilling and oilfield technology to Russia. Here are three articles looking at this issue from different perspectives.
"U.S. oil giant Exxon Mobil began drilling in Russia's Arctic on Saturday, despite Western sanctions imposed on its Russian partner Rosneft, and was hailed by Russia's president as an model of "cooperation".
BRICSPOST - Exxon Mobil Starts Russian Drilling with US Sanctioned Rosneft
"Russian President Vladimir Putin on Saturday gave the start signal through a teleconference for joint drilling in Russia’s northernmost offshore exploration well. Russian state oil company Rosneft and US oil and gas giant ExxonMobil have gone ahead with the drill, sidestepping the strain in US-Russia relations over Ukraine and subsequent round of Western sanctions on Russia."
Russia Today - ExxonMobi, Rosneft Start Joint Arctic Drilling in defiance of sanctions
"US oil giant ExxonMobil and Russia’s Rosneft will continue joint exploitation of the Russian Arctic despite Western sanctions, the American company said as the two giants launched exploration drilling in the Kara Sea.
"Our cooperation is a long-term one. We see great benefits here and are ready to continue working here with your agreement,” Glenn Waller, ExxonMobil's lead manager in Russia, told President Vladimir Putin during a videoconference call."================================================================