Degradation of crude oil occurs when:
– Heating above 30 deg C, the light hydrocarbons such as Butane and Natural Gasoline may evaporate; this lowers the potential yield of gasoline and lowers the price of the crude. With SPR underground tanks, this is not an issue because of the year-round constant temperature of about 17 degrees C in the SPR underground salt caverns.
– Mixing two crudes with differing fuel fraction yields; it may lower the refiner yield of the most profitable products and thus lower the crude blend value to the refiner. This is determined by examining the resulting blend “assay” of the two or more different crudes.
– Mixing “incompatible” crudes or hydrocarbon such as highly paraffinic crude; this may precipitate asphaltenes, which will form a sludge, which coats the tank walls and internals of pipes and pumps. This does not render the crude unusable; it is a headache, and it just increases the cost of pumping and sludge removal, and maintenance costs.