The mobile self-elevating (drilling) unit, or jack-up, has been central to the exploration and development of offshore oil and gas reserves. In recent years there has been an increased desire to benefit from the potential economics of using these units in longer term production roles either in association with a fixed platform or as a stand-alone facility. However, until recently there had been no concerted effort to develop a consistent and commonly accepted standard for general industry use in site specific assessment of jack-ups.
This paper describes the background and work carried out to develop such a standard. The project is nearing completion and has resulted in the publication of a Guideline document.[11 A Recommended Practice and Associated Commentary are (at the time of writing) in the final stage of drafting for release to the project sponsors for trial and comment prior to issuing the first Edition early in 1994.
One of the prime attractions of the jack-up is its mobility. Once a particular deployment is complete it can be transferred on its own buoyancy, with minimal outside resources, to a new location. The marine aspects of the jack-up have traditionally led to the design being carried out in accordance with classification societies' rules, the first of which were published in 1968. These rules and jack-up design practices have evolved based on successful performance and using well established technology.
A jack-up is normally designed to a set of generalized criteria for the elevated operational mode. A classification society's independent review ensures compliance with both their Rules and other industry standards. The use of such generalized criteria allows maximum flexibility for utilizing the unit in service worldwide and it has been the responsibility of the owner to operate a unit within its design limits.
When a jack-up is operated at a particular location the owner needs to assure himself that the location parameters are within the benchmark limits of the unit and that the foundation is suitable. Should one or more of the criteria for the location fall outside the limits of the unit, it is necessary to carry out a site specific assessment to ensure the integrity of the unit and its foundation. In recent years some oil companies and national regulatory authorities have taken a serious interest in the engineering and geotechnical aspects of jack-ups. These oil companies have required site specific assessments to ensure that jack-ups meet their company's standards, which were developed in harmony with fixed platform design practice. Consequently, the owner has sometimes been required to produce location specific studies for various parties and to different standards.
Furthermore, the use of jack-ups was also extending to deeper waters and more hostile environments. The need to establish consistent and generally applicable criteria was recognized by Shell U.K. Exploration and Production, herein referred to as Shell. In 1987 Shell Commissioned Noble Denton and Associates to conduct an industry wide study to evaluate industry practice at that time.
