This article presents technical aspects concerning the design of a Floating Offshore Wind Turbine (FOWT) that is devised for supplying energy to a subsea water injection system (SWI) in a deep-water region. The main purpose of the project is to replace the conventional energy supply provided by gas turbines by wind energy, thus contributing to the decarbonization of offshore O&G production. The water injection scenario was defined by Petrobras and includes subsea pumps with power distribution and control system placed on- board the FOWT. The FOWT substructure and its mooring system were dimensioned by means of a coupled optimization procedure, which took into account the metocean characteristics of the site by means of long-term series of combined wind, waves and current data. A BESS (Battery Energy Storage System) was adopted to stabilize the off-grid electrical system and optimized to limit the subsea electrical motors stoppages. Aiming to provide realistic estimates of injected water volume, typical wind turbine efficiency factors and fault rates were considered in the analyses together with repair times calibrated according to the application scenario.