Simplification and Cycle Time Reduction - Design and Construction of the Mars TLP Hull
Authors: Balint S.W. , Kenney J.J. , Miller B.H. , Resweber L.R. , Smith P.L. , Marshall R.W. , Biello B. 
Published: October 2008

The. Mars TLP, Shell Offshore Inc.'s second TLP, was designed and fabricated in 30 months, a significant shortening compared to the previous effort. Being on the critical path, the schedule for the hull provided a large portion of the time savings by overlapping the design and fabrication schedule, simplifying the systems, revamping the approach to quality assurance, executing a record setting dry transport, and more. This paper examines each timesaving idea, describes the steps involved as well as the potential benefits and risks, and evaluates the outcome with respect to its actual time compressing value.

The items documented in this paper will be of interest to designers, project management, and fabricators involved inthe execution of large scale projects.

Introduction

The Mars TLP is Shell Offshore Inc.'s second tension leg platform (TLP). It was designed, fabricated, transported and installed in a significantly shorter period than its predecessor, the Auger TLP. Since delivery of the hull to the integrationsite dominated the project critical path, project acceleration was achieved by creatively compressing hull tasks. The most significant methods, the use of a "design-while-build"strategy, simplified systems, a new approach to fabrication quality assurance, and a dry transport of the hull, are discussed, showing the benefits as well as stumbling blocks encountered along the way.

Many of the ideas for improvement grew out of the experience on Auger, while others were conceived, developed and implemented in answer to immediate challenges imposed by the aggressive schedule. Still others were captured and implemented on subsequent TLPs.

Design While Build

When first determined to be project worthy in January 1993, the Mars prospect development was envisioned to require 43 months from design to first oil. This was based on the Auger schedule, modified to account for the difference in structure size and the elimination of the lateral mooring system (LMS), and accelerated to account for experience. Throughout the fabricator selection process, alternative methods of design and construction were reviewed in order to reduce the time between initial design and the beginning of fabrication. By August 1993, when Belleli SpA was selected, the total period had been reduced by 13 months. The detailed design period, sandwiched between the final configuration selection and the beginning of fabrication, was modified to provide most of the time savings.

The elimination of more than a year from the schedule was the result of several initiatives and appropriate risk taking. Belleli adopted an aggressive approach to the project and put into use a computerized system for project management and shop drawing production. They also embraced phased drawing releases in their technical proposal. This concept helpedextend the design schedule by requiring drawings only as they were needed, rather than all at once. An alternative contracting approach (reference OTC 8370) established a structured method for considering scope changes, allowing attention to remain focused on the project objectives. Inaddition, a detailed and extensive construction review was conducted, aimed at simplifying arrangements and details.