Despite the downturn in the industry, a new generation of Semi Submersibles has been developed and put into operation. This so called fifth generation of Semi Submersibles has ambitious goals in regards to operational safety and efficiency. The rig concept includes new ideas on how to make-up and run drillstring components, riser pipe as well as casing and tubing. Doubles, Triples or even Quadruples of pipe are being made-up at special "Mouse-hole stations" including their own mechanized handling and make-up equipment. By this means, many functions such as prefabrication of stands of risers, drill pipe and casing stands can be carried out offline without interrupting or delaying drilling operations. Considerable time- and cost saving is anticipated.
The paper describes the planning, development and implementation of the modular concept of the PowerFrame carrying the fully remote controlled power tongs that were installed on three of those rigs built in Brest/France and in Singapore. Actual field experience from a drilling location was not available when this paper was written (May 2000), as the first rigs are scheduled to arrive on location by June 2000. However, during the commissioning sufficient experience was gained to allow the prediction that the ambitious goals set in regards to time saving will be achieved.
Most rig building activity is led by long-term targets that are not very much affected by short term variations in the daily oil price and the related variations in drilling activity. Many new offshore rigs are built for deepwater conditions, specified by a water depth of at least 3,500 ft in that the rigs are operating.
The new challenges of drilling on those water depths require completely new concepts to cut down the well costs to an economically acceptable limit. The costs of a well is directly related to the daily costs of the rig, but of course also to the duration of the drilling operation necessary for each well.
To complete a well requires the task of actually drill the well, with the rate of penetration being the important factor to determine the time it takes to reach a certain depth. The second factor are the flat curves in the drilling progress curves where no further depth is reached, due to activities such as tripping, logging or running casing and cementing.
A "new generation" of floating rigs must therefore follow new guidelines and procedures to be able to reduce costs . The Sedco Express rigs (Fig. 1) are a new type of floater that make use of measures to reduce both, drilling time as well as flat time. Drilling time is reduced, for example, by specifically designed, strong mud pumps.
Flat times are reduced by a new concept of tripping as well as riser pipe and casing handling, that includes the mechanized handling of pipe as well as automated make-up of all threaded connections.
The ambitious goal of these measures is to reduce the total time on location by 25%, and associated well construction costs by 30%.
Three of these rigs were built, respectively are currently under construction; the Sedco Express and the Energy Express in Brest as well as the Cajun Express in Singapore.