I'm no geologist, but I did sleep at a ... no I slept at home last night, never mind.

I wonder, since extracting the oil probably leaves cavities. I would think some or a lot of the "refilling" is oil being squeezed out of the cracks in the surrounding rocks. But's that's an off-the-cuff thought.

I seems remember water is frequently pumped in to maintain pressure. But is that done in the desert?

Edited to typo a correct.