This article describes about basic information of jack up legs – Cylindrical Legs vs Trussed Legs, Three-Legged Jack Up vs Four-Legged Jack Up and Three-Chorded Legs vs Four-Chorded Legs.
Cylindrical Legs vs Trussed Legs
Since the hull needs to stay above the storm wave crest, withstand certain pressures, and transmit different loads between the footing and hull, every Jack Up unit will have legs of some sort. Similar to the footings, there are two different types in trussed legs and cylindrical legs.
Cylindrical legs can vary slightly but the basic premise involves hollow steel tubes. However, some units will have internal stiffening and others may have rack teeth or small holes to allow the hull to move up and down the legs. Generally, these cylindrical legs are used on units that stay shallower than 300 feet of water depth. With the newer units that are designed to work in environment deeper than 300 feet, they tend to use trussed legs and this is because trussed legs require less steel for the same resistance and same elevated response.
Figure 1 – Cylindrical Leg Jack up (dsboffshore.com, 2018)
Jack up units have footings to increase bearing area of each leg. This will result in reduction of load capacity of soil to deliver a firm foundation for a jack up rig to stand and transfer weight to the sea floor . With two different types of footing, spud cans and mats, it is important to know the main differences that exist.
A Jack Up is a type of offshore drilling rigs. It is made up of a hull, legs, and a lifting system and a jack up rig can be towed to the offshore site, and then lower its legs into the seabed to lift up the hull, providing a stable work deck which is strong enough to cope with the required environmental loads.
Another advantage of Jack Up rigs is that they can operate in high wind speeds and with significant wave heights, as well as in water depths reaching 500 feet. Since the Jack Up will be ultimately supported by the seabed, they are usually preloaded upon arrival at the intended site to simulate the kind of leg loads that they will be exposed to. This ensures that once the rig is fully jacked up and in operation, the seabed will be able to provide a strong foundation for the rig.
The offshore industry has made significant use of Jack Up rigs for over 60 years now. They are especially useful for exploration drilling since they are relatively easy to set up, and also provide ample production, accommodation, and maintenance areas. Over the years, Jack Ups have been pushed to their limits in terms of what they can do. This includes their deck load carrying limits both when afloat and when elevated, their environmental and drilling limits, and the soil, or foundation, limits. By pushing these limits, drilling companies have been able to explore deeper waters, drill deep reservoirs in harsh conditions, and even drill in areas with unstable soils and foundations. Continue reading →
In our opinion, it is very interesting decision made by Transcoean to sell all jack-up fleets to Norwegian offshore drilling contractor, Borr Drilling. With current oil market situation, Transocan has made decision to stay only deep water drilling.
Please feel free to share your thought about this.
News by Offshore Energy Today
Norwegian offshore drilling contractor Borr Drilling, formerly known as Magni Drilling, is planning to buy 15 jack-up drilling rigs from Swiss-based Transocean for $1.35 billion.
Borr Drilling announced on Monday the signing of a letter of intent with Transocean for the acquisition of 15 high-specification jack-up rigs.
The transaction consists of Transocean’s entire jack-up fleet, including ten rigs already in the fleet and five newbuilds under construction at Keppel FELS Limited, which Transocean has been postponing for a while now. The latest agreement with Keppel entailed the deferral of the five new jack-ups until 2020. Continue reading →
Perro Negro 6 Incident – Jack up rig capsized and sank was happen few year ago but we would like to share this case as a case study. You can watch what happen in the video below.
It is clearly seen that the rig capsized and sank in just few minutes. Jack up rig move is one of the most hazardous operation. Before a rig is moved, total number of people on board will be kept at minimum for operating the operation and non essential personnel will not be allowed on the rig. There are several considerations that rig contractors and operators must be agreed before commencing any rig move operation. For this case, we would like to emphasize that even though all safety is in place, the bad thing can be happened.