Rigs Flashcards
What is the water operation depth max / range of following rigs Jack-up Semi-sub Fixed Platform Drill ship
Jack-up 400ft 10-120m
Semi-sub 10000ft
Fixed Platform 1500 conv. 3000 max
Drill ship 10000ft
Stats of a typical heavy land rig Depth rating Pump power Rig staff Day cost
Depth rating 6000m
Pump power 3200hp
Rig staff 60
Day cost 30k - 50k 2014
What is pre-loading?
24 hour waiting period when installing a jack up rig to let the legs settle on the sea floor whilst platform is only just out of the water. During the period all mud and other tanks are filled with water to add extra weight.
What is the benefit of having a sliding Derrick on a jack up rig?
Enables you to drill around an existing platform as you can get close and then move the Derrick over the existing platform. The same jack up rig, without moving the jack up can then drill ten holes in one go.
What is a riser pipe used for?
Runs from the top of the conductor up to the drilling rig. Conductor will commonly be installed on a fixed platform in a well casing. Jack up rig will then come in and drill over the top through the conductor, needing a riser to join platform level conductor up to the rig.
Where is the Christmas tree and blow out preventer on a floating rig?
Sea bed not the platform.
How does a semi submersible rig overcome wave movement issues?
Similar to two submarines, not impacted by wave movement, keeping a constant depth, there are then two legs up and the rig is suspended on the legs in the air. Wave action only then impacts the legs limiting wave movement
Semi submersibles in 1000mt would need 5000mt of anchor cable with extraordinary weight etc. how are semi submersibles alternatively “anchored”?
GPS driven lateral thrusters that hold the rig in place. It requires 60tonnes of diesel $60k per day to hold the rig in place.
What is a traveling joint?
Used on an FPSO which is going up and down in the water, the riser is connected to winches / hydraulics that keep the “hold” on the riser at a fixed level, necessary as riser fixed to the sea floor and would otherwise snap / sever.
The 20” riser pipe very heavy at a mile deep it can be covered in polystyrene to help minimize the weight on the rig.
What drives the decision between FPSO and semi submersible?
- Weather- semi submersible more stable, FPSO more sea roll
- Archimedes FPSO displaces far more water and thus higher load capacity. A semi submersible only displaces the water volume of the legs so it has relatively low load capacity, this requires each round of casing to be loaded separately (far higher logistic costs) and impractical to use if a long way away from supplies, ports etc
What is a TLP and what’s its key advantage?
Tension leg platform. A steel manifold is built on the sea floor and a semi submersible is the “anchored” to the manifold using steel pipes. The semi-sub is the pulled down against the force of the pipes and against its own buoyancy creating tension in the legs which keeps it a constant height. Whilst there will be lateral movement this means you don’t need a traveling joint and can therefore have the Christmas tree at surface rather than subsea!
Usable upto 7000ft
Biggest thing ever moved on earth?
Troll platform. 1 million tons. 472m high.
