A seabed supported unit for drilling and production of hydrocarbons, comprising a seabed supported base structure (10) positioned and fixed with respect to a sea bed (11), forming a support for a floatable drilling unit (30) and/or a floatable production unit (50), characterized in that the base structure (10) is provided with buoyancy devices, an upwards extending wall structure (15) extending around the base structure (10) along three sides, thereby leaving an opening (15′) along a fourth side of the base structure (10) for introducing the floatable drilling and/or production unit (30, 50), retractably arranged on top of the base structure (10) and within the upwards extending wall structure (15), and the upwards extending wall structure (15) is provided with one or more cantilever units (13) each extending laterally out from an exterior side of the upwards extending wall structure (15), each cantilever unit having prepared well points for drilling of wells (12) and terminating above sea level (25), forming a structurally integrated part with the upwards extending wall structure (15).