A Classification Society's Approach And Requirements For Conversion Of Mobile Jackup Units To Site-Specific Production Units
Authors: Rajapaksa Y.R. , Chang K.T. , Tan Pao-Lin 
Published: June 2014

This paper presents ABS approach and requirements for classification of mobile jack-up units converted to site specific production units. The classification process provides the framework to determine the structural fitness of the unit to fulfill its intended purpose of conducting safe operations at the specified location.

This paper also describes the statutory requirements of the Mineral Management Service (MMS) of the U.S. Department of Interior and the United States Coast Guard (USCG) for jack-up units converted to site specific production & its to operate in the Gulf of Mexico.

INTRODUCTION

The drop in oil prices in recent years has encouraged offshore field developers to look for cost effective concepts for producing oil. One of the concepts being considered by many field developers is the conversion of existing jack-up units to site specific production units. Given the availability of existing jack-up units in the market and the possibility of immediate conversion by installation of the process equipment, a viable and an attractive alternative to traditional fixed platforms for marginal fields worldwide becomes available. Another attraction of the jack-up unit is its mobility. Once a particular deployment is complete it can be moved to a new location with minimal outside resources.

For a given field, the selection of the most optimum jack-up unit for conversion depends on many factors. Two factors that play an important role are the fitness of the unit to operate at the new site and the hull modifications required to support the equipment. The fitness of the unit is determined by demonstrating that the unit has adequate strength and foundation stability to withstand the environmental loads at the new location and has an acceptable remaining fatigue life.

The ABS classification provides the owner with a determination of the fitness of the unit to operate at a given location by complying with ABS Rules and Guides. The classification process of a jackup unit converted to a site specific production unit involves: a condition survey, review of the design, surveys during construction / modification and installation, and in-service surveys. The condition survey is to assess the current condition of the unit, The review of the structural design of the unit consists of an evaluation of the design criteria and pertinent environmental and geotechnical data followed by a review of the submitted structural assessment, foundation assessment and fatigue assessment of the unit. The structural assessment should indicate the adequacy of the unit with regard to strength and overturning resistance. Foundation assessment should indicate the adequacy of the soil resistance against bearing and sliding. Fatigue assessment of the unit should indicate the adequacy of the remaining fatigue life.

Construction / modification surveys monitor all fabrication work performed for the conversion of the jack-up unit to a site specific production unit. The site installation surveys establish the global condition of the unit at the site to facilitate yearly monitoring of the unit.