“They will be able to buy gas cheap, on the spot market without investing anything.”
Likely the case, they’ll just buy the gas being freed up from Europe trying to get off of Russian gas.
They Fake News Media may make it sound like the fear of sanctions was the driver (to try to drive a wedge between Russia and China), but much more likely just a SIMPLE business decision - Russia will have a BOATLOAD of gas to export now, so why invest to give Russia even more gas to export?
They will need investment to give Russia the ability to export that gas to China.
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