UPDATE 1-Shell JV Deer Park, Texas refinery begins planned overhaul -sources

(Adds company statement, details on units)

HOUSTON, Sept 23 (Reuters) - Royal Dutch Shell Plc began a planned overhaul at its 340,000 barrel-per-day (bpd) joint-venture Deer Park, Texas, refinery on Monday with the shutdown of the large crude distillation unit (CDU), sources familiar with plant operations said.

In addition to the 270,000 bpd DU-2 CDU, Shell will overhaul the 92,000 bpd coker and the 67,000 bpd hydrocracker along with several other units. The work is scheduled to run between six weeks and two months, the sources said.

Shell spokesman Ray Fisher said planned work was underway at the Deer Park refinery.

DU-2 is the larger of two CDUs doing the primary breakdown of crude oil into hydrocarbon feedstocks for all other production units at the refinery.

The coker converts residual crude oil from distillation units into feedstocks for motor fuels or petroleum coke, a coal substitute. Hydrocrackers use hydrogen under high pressure and high heat with a catalyst to convert gas oil into motor fuels, primarily hydrogen.

The Deer Park refinery is a 50-50 joint venture between Shell and Pemex, Mexico's national oil company. Shell is the managing partner. (Reporting by Erwin Seba; Editing by Will Dunham)