Bennett Offshore

Jack Up Units - A Technical Primer

In 2005, Bennett Offshore and Offshore Technology, Inc. (Keppel FELS) co-authored a document titled "JACK UP UNITS - A Technical Primer For The Offshore Industry Professional." It is available for free upon request via a form on this website.

The intention of the jack-up publication was to provide Offshore Industry personnel and others with a brief introduction to jack-up platforms and their design considerations. This document has since become known simply as "The Jack-up Primer" and is widely used in the industry as "required introductory reading" for personnel new to the Offshore industry. Of all the technical papers and publications authored by Bennett engineers, the Jack-up Primer is by far the most requested document.

Below, you will find selected text from Section 1 of the publication. If you wish to have your own copy of the Jack-up Primer or any of our other technical papers, please request a copy and we will send you as many documents as you need.

A Sample of Chapter 1 of the Jack-up Primer


1.1 SYNOPSIS OF A JACK UP

A Jack Up is an offshore structure composed of a hull, legs and a lifting system that allows it to be towed to a site, lower its legs into the seabed and elevate its hull to provide a stable work deck capable of withstanding the environmental loads. A typical modern drilling Jack Up is capable of working in harsh environments (Wave Heights up to 80 ft, Wind Speeds in excess of 100 knots) in water depths up to 500 feet. Because Jack Ups are supported by the seabed, they are preloaded when they first arrive at a site to simulate the maximum expected leg loads and ensure that, after they are Jacked to full airgap and experience operating and environmental loads, the supporting soil will provide a reliable foundation.

1.2 PURPOSE AND DISCLAIMER

Jack-up units are complex structures used Offshore in many modes of operation. When using a particular unit at a given site, it is important to be aware and understand the basics behind the different designs under different conditions. The focus of this primer is a simplified discussion of the various sensitivities of jack-ups while in the different modes of operation. It is hoped that by increasing the understanding of how jack-ups work and behave, as well as the sources of the loads acting on them, those making decisions with limited information will be better equipped to respond to incidents and reduce their occurrence and/or consequences. Though there are many variations in design and purposes for jack-ups, this primer focuses many of these discussions on three-legged units used for drilling.

The primer starts by presenting some background and discussions of the basics of jack-up components analyses. This is followed by sections on jack-up components and configurations, modes of operation, differences between Class approval and site specific assessment, basic analysis, and a discussion of competing aspects of jack-up design.

1.3 BACKGROUND

Jack-up units have been a part of the Offshore oil industry exploration fleet since the 1950s. They have been used for exploration drilling, tender assisted drilling, production, accommodation, and work/maintenance platforms. As with every innovative technology, jack-up units have been used to their operational and design limitations. These limitations include deck load carrying limits when afloat, load carrying capabilities when elevated, environmental limits, drilling limits, and soil (foundation) limits. The reasons for pushing these limits include the desire to explore deeper waters, deeper reservoirs in harsher environments, and in areas where soils and foundations may be challenging or even unstable.

Into this arena of expanding jack-up units' capabilities, industry groups, classification societies, and flag states have involved themselves in an attempt to regulate, codify, and unify the criteria used to gauge a jack-up unit's capabilities. Without a thorough knowledge of the background of these regulatory efforts and the science that these efforts rely upon, the average Offshore industry professional is given practically no useful tools when it comes time to assess, understand, and select a jack-up unit to fulfill a particular task or mission statement. Often times, a thorough understanding of Jack-up unit capabilities and "sensitivities" prevents or minimizes the consequences of unexpected "incidents." This primer is an attempt to assist such individuals in understanding the regulations, science and engineering principles behind a jack-up unit's design and to assist that individual in answering the following questions:

- What are the components of a jack-up unit and what are their functions?
- What are the relative pros and cons of different types of jack-ups and their features?
- How does the arrangement of a jack-up affect its function and capability?
- What are the loads on a jack-up, what impact do they have, and how are they evaluated?
- What do I need to look for - what makes a jack-up "sensitive" to loadings?
- Who are the parties involved in the jack-up from design through operation, and what are their roles?
- How do I select a suitable jack-up unit for my particular application?

This primer does not address commercial issues of jack-up rigs. Topics such as construction costs, day rates, third-party equipment, supply and crew boat costs, etc., are not covered in this primer.

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