Abstract: A device comprising a sleeve in the form of a cylinder to be placed over a defective deep-water subsea oil-well equipment structure such as a defective Blow-Out Preventor (BOP), said cylinder being anchored by suction anchors and including a roof in the form of a funnel and including pipelines for introducing methanol for preventing hydrates formation and pipelines for removing water/oil/methanol mixture, where the space between the inner wall of the cylinder and the outer surface of the sub-sea equipment may be filled with grout, is suitable for stopping run-away oil-well leakage. A process for stopping run-away oil-well leakage by using said structure is also disclosed.