The issue is that they never expended the infrastructure, never exploited new fields, their old oil field started giving less, so they pumped more water in, which probably lowered the quality of oil, and made it harder on the refineries.

Venezuela oil also need a lot of refinement in any case, and this is where the US made a mistake, because they could just have insisted on refining Venezualan oil rather than directly taking a cut, which will be seen worse by the locals. Basically help more venezualan crude oil to get out of the field than their refinment capacity can afford, and loan them tankers to sell the crude to US refineries. US corpos could have profited a lot more (and if the US could tax them, the US government could have taken a cut) than this weird, dumb and aggressive position of taking a cut.