Does anyone know if the caverns are filled with sweet of heavy crude, and will mixing them make any difference? Seems to me, the light would float on top of the heavy so it would just be a matter of which pipe is used to pump to oil.
Never advisable to do that. Pollutes the entire mix.
Crudes are complex liquids with different components. These include non-hydrocarbons such as sulfur which sours it.
They are categorized by similar types for using in specific refinery processes to generate products such as gasoline, diesel, jet fuels, lubricants, etc.