The Chinese are trying to do several things at once with these deals. First. they are trying to cut deals that will give them oil at a predictable cost, less subject to fluctuation than the spot price. Second, they are trying to obtain oil at a below market price by offering sellers the chance to have a stable long term deal. Third, they are trying to use their petro-purchasing power to leverage a geo-political advantage and to disadvantage nations they see as long-term strategic rivals - like the USA. Fourth, they are trying to substitute barter for cash whenever possible to ease pressures on their foreign excchange reserves.
All these actions are typical of a state-controlled economy and reflect weakness, not strength.
And yes, oil isn't PERFECTLY fungible. Thaat's why I said it is relatively fungible. There are big differences in the composition of crudes from around the world. Most refineries are optimized for particular crudes. Venezuelan crude, if I recall correctly, requires some special refining processes to deal with its high sulfer content. Still, I stand by my central point.
I agree with you. Chinese are bartering for sure as part of their Venezuelan and Iranian deals. You must pay cash when you buy fungible oil on the world markets