It awarded Saipem front-end engineering and design contracts in January for what would be the Asian nation's largest offshore field, with gas to be sent onshore for four separate gas-to-power projects to be run by different operators.
The importance of Blue Whale to Vietnam is huge as when fully operational the project may supply 10% of all the 96-million strong nation's needs at a time when it needs more power than ever.
It would also provide US$20 billion in revenue.
Though unconfirmed by ExxonMobil the narrative seems to be that recent issues in the South China Sea, with China sending its own oil rig to the Vanguard Bank and its militia to hassle and block operations by Rosneft, have helped dissuade the US supermajor from continuing its involvement in the contested waters.
This is only likely partly true.
While it's hugely unlikely the Trump administration would send forces to protect ExxonMobil from low-level Chinese harassment, the US has been especially strident in its criticism of China's recent actions and would likely double down were a US company affected.
The most likely reason for ExxonMobil selling out is that Blue Whale is that on a company scale it is a minor project in a non-core region at a time when the supermajor is looking to complete US$15 billion worth of divestments to streamline its portfolio to five key areas: the US Permian Basin, offshore Guyana, deepwater Brazil, Mozambique and the two LNG project expansions it is progressing in Papua New Guinea.
"The rest of the portfolio has to compete for capital with these world-class growth opportunities," Wood Mackenzie analyst Andrew Harwood told Energy News.
"I suspect it's already in a divestment box in an ExxonMobil office somewhere."
Vietnam expert Professor Carlyle Thayer at the Australian Defence Academy told Energy News he had heard China planned next to put pressure on the development after its harassment at Vanguard Bank.
"I was also told that China's foreign minister Wang Yi asked Russia's foreign minister Sergei Lavrov to get Rosneft Vietnam to cease its activities when they met in Bangkok on August 2 on the sidelines of the ASEAN Ministerial Meeting. Lavrov declined the request," he said.
China will likely not be able to force ExxonMobil's hand, especially with Vietnam's Communist Party Secretary General Nguyen Phu Trong, the most powerful of the nation's troika of leaders, on his way to the White House for the second time after an historic 2016 visit.
Should the Texas-headquartered supermajor simply spinoff Blue Whale the Chinese implications will loom far larger, and could derail one of Vietnam's largest energy investments.
The sovereign risks may make finding a buyer harder for what is a hard sell given the fields contain 30% CO2 in a time a sped up climate consciousness.
This has wider implications if you understand China's aims in the South China Sea past its military developments.
China's aim is to push all foreign oil companies out of the region and force all seven claimants of all or part of the South China Sea to develop their offshore resources only in partnership with Chinese companies.
"Given the moves being made by China, it's difficult to see who would have the appetite to come in, other than PetroVietnam (no money) or one of PetroVietnam's existing partners with strong government backing i.e a Moscow-headquartered firm," Harwood said.
"The field is firmly within Vietnamese maritime borders, but that hasn't stopped the Chinese interfering previously. Ultimately I think there needs to be a political resolution before we could get clarity on the project progressing."
For China, there is only one political resolution: dealing one-on-one with smaller claimant nations and enforcing its nine-dash-line, which The Hague ruled against in 2016 after the Philippines brought the case.
If Blue Whale is beached it will likely be another step in Beijing's plans to slowly develop the region's hydrocarbons with smaller nations struggling to say ‘no' if they cannot find their own farminees, though China developing the project would also likely cause tremendous domestic political unrest among the sometimes-Sinophobic population.