Marathon Galveston completing work, planning shutter of gasoline unit -sources

* Marathon preparing to restart crude unit, finishing FCCU repairs

* Marathon planning to shut smallest FCCU at Galveston Bay by mid-2016

HOUSTON, Oct 3 (Reuters) - Marathon Petroleum Corp is preparing to return a 218,500 barrel per day (bpd) crude distillation unit to production at its 451,000 barrel per day (bpd) Galveston Bay Refinery in Texas City, Texas after two weeks of repairs, sources familiar with operations at the refinery said.

The company is also finishing up repairs on the giant 120,000 bpd Fluidic Catalytic Cracking Unit 3, according to the sources. FCCU 3 is supplied with gasoil from Pipestill 3A and was shut when the crude unit was taken out of production. An alkylation unit was also shut for repairs when the FCCU was on Sept. 17.

Separately, Marathon has begun planning to permanently shut the smallest gasoline-producing unit at the Galveston Bay refinery by mid-2016, the sources said. (Reporting by Erwin Seba)