(Bloomberg) -- Royal Dutch Shell Plc (NYSE: RDS-A), the biggest oil company in Europe, said production director Andy Brown is taking leave to recuperate from recent medical treatment.

Maarten Wetselaar, executive vice president for integrated gas projects, will be acting upstream chief in addition to his duties until Brown returns, The Hague-based Shell said Jan. 20 in a statement without indicating when that might be. Brown had heart surgery, Upstream reported without citing anyone.

Brown, at Shell for about 30 years, became head of upstream operations in 2012. He has led the Pearl gas-to-liquids project in Qatar, the Anglo-Dutch company’s most expensive, and was responsible for the Qatargas-4 liquefied natural gas venture.

He was an internal candidate to be chief executive officer at Shell after Peter Voser unexpectedly quit last year. Ben van Beurden, a former refining executive, became CEO from Jan. 1.