Regarding the "Spectacular failure": You are looking at it very China centric. The spectacular failure is for Venezuela. The whole point of it was to deversify the purchasers of oil. What it did in reality is that it decreased the profits (because they need to ship it themselves now and further to China) and had marginal effect on diversification(At start majority of this "trade" went to the US with the Chinese basically pocketing the price of shipment in to their pocket). Right now, i am not 100% sure but i doubt that China all of the sudden built facilities to process Heavy Crude. Most of the facilities for that type of oil is in the US.
I discussed about this only in the standpoint of either Venezuela or the United States. In fact, China doing whatever stuff to whatever it has bought from Venezuela, does not change the fact that in the standpoint of Venezuela, their goods were sold to someone other than the United States. Therefore, in my understanding, a spectacular failure for Venezuela can only mean that they failed to sell stuff directly to anybody other than United States, and thus suffer economic collapse.