🔍 Key Concepts

• Offshore drilling vessel structure – how drill ships and barges are arranged under the derrick • Path for drill string and tools – what space is used to lower tools from the rig floor down to the seabed • Difference between a buoyant hull/structure and a vertical opening through the hull

💭 Think About

• Which term refers specifically to a vertical opening through the hull or deck that is directly over the well center and open to the sea below? • Which options instead describe general hull structures (like floats or pontoons) or openings in working decks that are not necessarily open all the way down to the sea surface? • On a drill ship, what feature allows you to work the drill string while the vessel stays afloat and protected from sea conditions around it?

✅ Before You Answer

• Verify which choice is defined as a walled, usually rectangular or circular opening through the hull, open to the sea, used for drilling operations. • Eliminate any term that mainly refers to buoyancy structures (used to float the unit) rather than a through‑hull opening. • Check industry terminology used on drill ships, semi‑submersibles, and drilling barges for the central opening under the derrick.