a semisubmersible mobile offshore drilling unit includes a submersible lower hull comprising a ring pontoon having a trapezoidal shape ; an upper hull having the trapezoidal shape ; three stability columns supporting the upper hull from the lower hull ; and a drilling rig . the modu may be operated in a tender assist mode or an independent drilling mode . the modu may be equipped to prepare , drill , and complete a subsea wellbore or to workover an existing subsea wellbore .