The Guidelineless Caisson Subsea Completion System

1. 0 Abstract This paper describes the design and operation of a guideline less caisson subsea completion system (GLLCS). The design evolved from prior experience gained from the development and successful installation of the oil industry's first guideline-assisted caisson completion. The guideline less version incorporates much of the hardware utilized in the first caisson completion; however, it differs in many -respects. Emphasis in the first design was to develop and prove critical downhole valves and connectors. Emphasis in the second version is to develop the methods and equipment necessary to run, orient, and land guideline less caisson components from a dynamically positioned (D.P.) drilling vessel using existing guideline less technology. A second objective is to reduce the height of completion components above the mud line to a practical minimum. Special features of the GLLCS include:A removable/reusable drilling guide base.A fine-alignment orientation system which allows the 30 inch conductor pipe, permanent guide template, drilling guide base, and BOP stack to be run any orientation.A completion riser disconnect system for D.P. vessel drive off situations.A surface tree reentry system.A multi-faceted flow line connection system. 2.0 Introduction In 1975, work began on a development program aimed at reducing the risk of damage to subsea completions by hazards such as ship anchors, trawler nets, icebergs and falling debris. As a result, the caisson completion system was successfully developed. In this system, critical pressure-containing components are protected by housing them within the 30 inch conductor pipe below the ocean floor. In the spring of 1981, the first caisson completion system was installed in the South China Sea for Shell International Petroleum. The system is described in detail in OTC Paper No. 4043 presented at the 1981 Offshore Technology Conference. The installation of this system proved caisson technology for water depths to 1500 feet. Subsequently, it was identified that caisson technology could be readily extended to deep water applications with several inherent advantages. 3.0 Application The GLLCS is particularly suited for use in heavily congested sub sea fields where several satellite wells are located close together and where the risk of damage to trees or flow lines by drilling or lay vessel mooring anchors is considerable. With minor modification, the system can also be installed in iceberg-infested waters where the threat of iceberg scouring is great and the need for emergency drive-off procedures are critical. Finally, the technology and experience gained from the development of the guideline less caisson system could play a key role in the successful exploitation of deep ocean petroleum reservoirs in the near future. 4.0 System Description 4.1 General (See Fig. 1) The GLLCS prototype tree design is a 3 X 3 X 2-inch, 5,000 psi W.P. marine completion installed on a 16-3/4-inch, 10,000 psi guideline less marine wellhead. The wellhead is modified to fit inside a 30 inch conductor pipe and accept a hydraulic slim line (8L) wellhead connector. The secondary design objective was achieved with the tree standing only seven feet above the mud line. Through the flow line (TFL) pump down capability is also provided.