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Rosneft and Eni started to drill the well, known as "Maria-1", in December.
The ultra-deep-water prospecting and appraisal well was being drilled using the Scarabeo-9 rig and Rosneft said this week it had a target depth of 6,126 metres.
Eni declined to comment. Rosneft did not reply to a Reuters request for immediate comment.