While the primary focus in Japan is on the developing problems at Fukushima, another key energy source is also under threat in the country.

From Bank of America Merrill Lynch:

The earthquake that struck Japan last Friday has shut down some of the major refineries in north-eastern area off Japan according to Bloomberg report. Based on nameplate refining capacity, the capacity loss (1.7mn bbl/d) accounts for about 36% of total Japanese oil refining capacities or 6% of Asia refining capacities, on our estimates.

The end result of this loss in production is capacity 500k bbl/d less then Japanese demand. The key winner in this is Korean oil refiners, which, according to BofA Merrill Lynch, will likely pick up for the reduction in Japanese output.
Note the impacted Japanese refiners in the northeast:
Japan Refinery Map