A sub-sea processing system for the production of oil and/or gas from one or more production wells (1), especially wells producing heavy oil in deep water and with high viscosity. The system includes, beyond the production wells (1), one or more injection wells (2) for the injection of produced water, a separator (3), a production pump (4), a water injection and circulation pump (5) and a heating arrangement (6). A water circulation and injection pipe loop (7) is provided to interconnect the separator (3), the injection and circulation pump (5), the heating arrangement (6), the flow control device (11), and the wells (1, 2) enabling circulation of heated water to the wells (1, 2) via the separator (3) and heating arrangement (6).