The SPS template forms a rigid base for mounting SPS equipment subsystems, carries preassembled and pretested equipment during installation, serves as a drilling template, and provides a firm foundation for seafloor operations: Design of the template and procedures for installation evolved through a three-phase program of feasibility studies, detailed engineering, and field construction and installation.
A template unit for the prototype 3-well SPS has been installed in 170 feet of water. This unit, a 90 by 120 foot structure fabricated from tubular goods and weighing 1,500 tons with pre-installed SPS production equipment, was installed using techniques developed for use in 2,000 foot water depths. The template unit was barged to location and launched in a conventional manner. After being brought alongside the drill vessel and rigged, the template was selectively flooded and keelhauled beneath the ship. The unit was lowered at a submerged weight of about 50 tons and oriented to a desired azimuth prior to being set on the bottom. Four foundation piles were installed and the template unit leveled on these piles to complete the installation.
The template can be retrieved after well abandonment by deballasting flooded members, severing foundation piles and well conductors, and refloating.
Concern over the feasibility and cost of conventional bottom-founded production platforms in very deep water prompted Exxon's consideration of a Submerged Production System (SPS). Initially the template was simply a large skid for mounting wellhead equipment and a production gathering manifold. Later on addition of production processing equipment, such as separation and pumping equipment, was considered. Feasibility and design studies indicated that routine maintenance needs could be fulfilled by a remotely operated manipulator system (MMS). Development of underwater production equipment proceeded to the point where proposals for a Phase I Feasibility Study of an ocean floor template could be solicited from marine contractors, Global Marine Inc. was selected for this initial work.
The Phase I study was conducted to examine various means for transporting an assembled system to the installation site, for getting it on the bottom, and for orienting and leveling the ocean floor equipment on a solid foundation. On the basis of this study, a generalized procedure was selected. A detailed engineering effort transformed the concepts selected into hardware for testing, field procedures, and fabrication drawings for the prototype template. An essential part of this Phase II study was a failure mode and effect analysis which subjected equipment and procedures to a systemized scrutiny and led to the elimination of weak spots in the design. Detailed engineering on the template was completed and fabrication initiated. Procedures for mobilization and offshore operations were continuously refined until offshore activity began.
The need to interface with other subsystems will become apparent as this paper traces the design of the template structure and emplacement procedures. The installation concepts pursued, as well as major alternatives rejected, and the impact installation methods have on the template structure are discussed.
