Jack up rigs

Drilling Jackets are small steel platform structures which are used in areas of shallow and calm water. A number of wells may be drilled from one jacket. If a jacket is too small to accommodate a drilling operation, a jack-up rig (see below) is usually cantilevered over the jacket and the operation carried out from there. Once a viable development has been proven It is extremely cost effective to build and operate jackets in a shallow... 

Particularly for jack-up rigs, site surveys may have to be carried out prior to each reemployment to ensure that the rig is positioned away from the previously formed footprints (depressions on the sea-bed left by the jack-up legs on a previous job). 

Jack-up rigs. For drilling in water depths of up to 400 ft (122 m), the legs are cranked downward until they reach the sea floor and then jacked up so that the platform is 15 to 30 ft (4.6 m to 9.1 m) above the surface. Workers often reach the rig by helicopter (left). 

Design loads on a jack-up rig. (After McClelland, B. et at, Avoiding jack-up rig foundation failure. Symposium on Geotechnical Aspects of Off shore and Nearshore Structures, Bangkok, Thailand, A.A. Balkema, Rotterdam, the Netherlands, pp. 137-157,1983. Reprinted with permission from Geotechnical Aspects of Coastal and Offshore Structures, Copyright Taylor Francis Group.)... 

The primary hazard with the presently used jack-up rigs is the risk of punch-through in layered soils, when one of the legs suddenly penetrates a relatively stiff layer as shown in Figures 10.48 and 10.49. The resulting sudden settlement of the structure may severely... 

Most jack-up rigs are supported on individual pads or spud cans with 12-16 m diameter as shown in Figure 10.50. The base is often enlarged in order to increase the bearing capacity. The typical load in each leg can be up to 45 MN or more. The main limitation of this type of foundation is the low bearing capacity in very soft soil and the risk of... 

Broms, B., and James, D. J. E. (1985), Foundation problems with jack-up rigs in East China Sea, Proceedings of the 2nd Shanghai Symposium on Marine Geotechnology and Nearshore/ Offshore Structures, Tongji University Press, Shanghai, China, pp. 3-31. 

Young, A. G., House, H. R, Herlfrich, S. C., and Thumer, D. (1981), Foundation performance of mat-supported jack-up rigs in soft clays. Proceedings of the 13th Annual Offshore Technology Conference, Houston, TX, 4, pp. 273-284. 

Behai 2 (jack-up rig) China Gulf of Bohai, 1979 72 fatalities Capsized in storm while being towed... 

Usumacinta (jack-up rig) Gulf of Mexico (Mexico), 2007 22 fatalities Collision with production platform Kab-101, fire. 

Mediterranean Sea, Egypt, Offshore Oil Production, Explosion and Fire Fire during well control incident (blow-out) on production platform spread to nearby jack-up rig. 

Floating exploration and production facilities are sometimes provided on jack-up rigs, semi-submersible vessels, or ex-crude oil shipping tankers converted to production treatment vessels. These facihties are essentially the same as fixed offshore platforms or installations except they are moored in place or provided with a temporary support structure instead of being provided with fixed supports to the seabed. The major process fire and explosion risks are identical to the risks produced on offshore platforms. They have one additional major facility risk, which is the maintenance of the buoyancy of the installation. Should a fire or explosion effect cause a loss of buoyancy (or even stability), the entire facility is at risk of submergence. Adequate compartmentalization and integrity assurances must be implemented in these circumstances. 

---