You have to drive the 'stuff' to 'somewhere' to turn it into 'whatever'.

The stuff costs more in CO2 to drive to the place than you get from turning it into 'whatever'.

But is this a general and inescapable rule?

I think that would be a very interesting question to try and address in a meta-analysis.

That would defeat the purpose. Burning the bio-oil to extract energy from it would just pump CO2 into the atmosphere.

Yes, I understand that, but I thought that most of the CO2 is bound to the ash that's supposed to be buried underground? So there would be a net reduction of CO2, even if the bio-oil was burned?