HANOI, Aug 10 (Reuters) - Vietnam's Dung Quat oil refinery has processed its first batch of Russian Sokol crude oil on a trial basis, as it seeks a replacement for shrinking domestic Bach Ho output, its operator Binh Son Refining and Petrochemical said on Monday.

The 130,000-barrel-per-day refinery imported more than 710,000 barrels of Sokol crude oil last month to mix with other types of crude oil for the test run, Binh Son said in a statement, adding that Sokol accounted for 20% of the mix and Bach Ho crude 29%.

The processing of Sokol crude oil "is an important milestone in Dung Quat refinery's efforts to diversify its crude oil sources," Binh Son said.

"The processing result has shown that Bach Ho crude oil can be replaced in the future."

The refinery in the central province of Quang Ngai, which became operational in 2009, was designed to use crude oil from the Bach Ho field offshore Vietnam.

Output from that field has been shrinking in recent years, however, prompting the owner of the refinery, state-run PetroVietnam, to look for imports and plan to upgrade the facility.

Last year, Dung Quat processed its first batch of West Texas Intermediate (WTI) and Bonny Light crude oil.

PetroVietnam said Dung Quat would import 8 million to 10 million barrels of these two types of crude this year.

The refinery will shut down later this week for maintenance until early October. (Reporting by Khanh Vu; Editing by Martin Petty)