Growing friction between the chief executive of Brazilian state oil company Petróleo Brasileiro SA PBR -1.34 % and its board is threatening to hamper the company’s efforts to shore up its finances, people familiar with the matter said. An oil-workers strike launched Sunday has shut down up to 13% of Petrobras’s daily crude production , crimping the company’s already weak cash flow. In addition, continued upheaval in the boardroom is raising fresh concerns about a leadership vacuum as the company struggles to pare a mountain of debt. On Tuesday, Clovis Torres, a board member standing in for Chairman Murilo Ferreira—who took an unexplained leave of absence in September—abruptly resigned for “personal reasons,” the company said. Another director, union leader Deyvid Bacelar, who was elected to represent Petrobras employees on the company’s board, was arrested during a small protest as part of the strike on Monday and briefly […]