Auger's Lateral Mooring System: Key Learnings

ABSTRACT Installation of the Auger TLP was completed in February 1994 with fit production in April 1994. The lateral mooring system (LMS) was critical to the successful mating of the hull and deck and installation of the tendons. The LMS is currently used to position the TLP over the wells during drilling operations and to assist the tendons in holding station during storm events. This paper describes the most significant lessons learned duringdesign, fabrication, installation and operation of the LMS. me results presented in this paper will be useful to mooring system designers, component manufacturers, installation contractors and other operators pursuing floating system options for development of deepwater fields. Specific results to be addressed include design criteria component selection, corrosion protection systems, component manufacture, anchor performance, locked coil failures, buoy pin retainer failures, line tension measurements, installation procedures and offshore operations. ?the most significant aspect of this paper will be to provide the industry with the key Iearning from the Auger LMS so that deepwater mooring systems maybe further improved for future applications INTRODUCTION Auger's LMS is a combination wide chain mooring system with submersible buoys and drag embedment anchors secured on the TLP by linear winches (See Figure 1). The entire winching system, except for the bending shoes, is located in the TLP hull columns (See Figure 2), Each of the eight mooring lines has a minimum breaking strength of 2900 klps. All components are corrosion protected, except the chain, and designed for a 30 year service life, An overview of the Auger LMS is presented in Ref. 1. A general discussion of lateral mooring systems for TLPs is presented in Ref. 2. SYSTEM DESIGN Numerous studies were performed in-house, with mooring component manufacturers, and with outside consultants to optimize the LMS configuration in terms of performance, COSL weight and schedule. Joint Industry Studies conducted by Noble Den ton (DMOOR mooring analysis program, Wire Fatigue, Chain Fatigue) and Aker Omega (Large Scale Anchor Test) provided valuable information that influenced the LMS design. The LMS design also built on the experience gained from the Lena guyed tower (Ref. 3) and Placid FPS (Ref. 4) mooring systems. Design Criteria The LMS was designed by Shell in accordance with API RP 2FP1 (Ref. 5) and additional criteria developed within Shell. Limits were placed on ?TLP offset line tension, anchor loads, buoy depth and fatigue for both operating and design conditions. Higher safety factors were specific for the operating condition where the LMS is used to pull the TLP over an outermost well. Line dynamics and line fatigue were analyzed during the design process. A detailed description of the LMS design criteria is presented in Ref. 1.