This paper describes a new concept for maintaining and repairing deepwater pipelines based on a sound, cost effective, modular approach utilizing remote work systems. In a significant departure from previous pipeline repair system designs, this concept has been developed as a more universal deepwater production work system with the potential for multiple work task capabilities. To further illustrate this capability, the paper discusses one of the ROV based work modules, an abrasive waterjet cutting system, which has a wide range of potential applications.
In 1981 Gulf Oil Exploration and Production Company (now Chevron USA) began studying a system for deepwater pipeline repair and production facility support for use in water depths to 8000 fsw. The study focused on this area of concern because the development of deepwater reserves will require production systems, infield flowlines and pipelines in water depths beyond the then current industry repair capability of 1000 to about 1500 fsw. This early feasibility work (Phase I of a total development program) resulted in a Joint Industry Project to develop the preliminary design of a sound, cost effective approach to performing pipeline repairs in water depths to 8000 fsw (Phase II). Building upon early feasibility work, Gulf proceeded with the preliminary design of a modular system approach to pipeline repair with Chevron Corp., Exxon Production Research Co., and Mobil Research and Development Corp. as participants in the Joint Industry Project. A preliminary design for the Deepwater Production Work System (DPWS) was completed in June 1985.
While the emphasis of the program has been on pipeline repair capabilities the DPWS also appears to offer significant promise as the basis for a general subsea intervention and support system. The DPWS design relies heavily on existing technology, tools, subsystems and proven operational techniques. The modular design of this system ensures flexibility and enables the DPWS to be adapted to a variety of underwater work tasks, including flow line and pipeline construction and repair, as well as subsea production system installation, service, and maintenance. The results of the project to date have shown that the DPWS is feasible and can be constructed using existing technology.
This paper will briefly describe the Phase II project and the resultant DPWS system and will further emphasis it's modularity, flexibility and versatility for a variety of subsea tasks by further describing a work module that has been envisioned for use with the DPWS. The development of this work module is the focus of a proposed ongoing effort to develop the DPWS system (Phase III).
The objectives of Phase II were to define and develop an economical repair technique with a modular work system. The development program was to accomplish the following: