The maintenance is expected to start in the second-half of September, the sources said on Friday, although exact dates were not immediately known.
A spokesman at SK Innovation, that owns SK Energy, declined to comment.
The shutdown would reduce South Korea's crude and condensate imports and is positive for fuel sellers in a market awash with oil products, traders said.
Asia has surplus middle distillates but is short of naphtha and fuel oil.
The Incheon maintenance will coincide with turnarounds held by S-Oil Corp and Japan's Cosmo Oil and JX Nippon Energy.
SK Energy also operates an 840,000-bpd refinery in Ulsan.