A drilling tender for production wells enables round-the-year drilling to a conventional depth of 4.5 km. The tender is a submersible mobile facility fixed to the seabed with piles. To do drilling in ice conditions, the platform has endurance at least 90 days with regard to process inventories. With the platform, a protective caisson can be mounted on the seabed for subsea well completion; drilling from a satellite platform is also possible for surface well completion.