Critical Points For The Project Of Very Deep Subsea Completions (1988)

ABSTRACT Some critical points, which should be considered for the project of very deep subsea completions, are analysed on the paper. Adaptations in the subsea hardware to permit intervention with ROV's due to the impossibility of using saturated diving; use of lay-away conception for the pull-in of the flowlines; and installation of diverless Wet Christmas Tree using dynamic positioning vessels are some of the discussed topics. It is also shown the aplication of those concepts to the pilot floating production system project of the giant Marlim field, which will be put onstream in 1989. SIMPLICITY: A PHILOSOPHY TO BE ADOPTED The installation and operation of more than one hundred Wet Christmas Trees in Campos Basin have shown that simplicity is always the best solution for the problems which might arise during subsea completions. The different tree' models from 5 manufacturers have made possible a firmly based evolution showing the way to follow to very deep waters. By the end of the "seventies", we started subsea completions in Brazil using very sophisticated equipment, mainly because some of the possible problems were overestimated by either the designers or the operator. Today it is known that some of the equipments that have been used are very reliable, while others were a constant source of problems. The solution of these ones have turned out to be, in the majority of the cases, much simpler than those concepts used in the original equipments. For instance, we have replaced all the diverless pull-in hardware (skids, frames, pull-in tools, etc) by the lay-away concept whose reliability has already been field-proven. An aspect which also confirmed our point of view was the performance of the original "diverless" equipment which had basically two problems:they seldom worked without the use of divers.not foreseeing divers intervention, they normally made the underwater work harder. The general result was a more time consuming and less cost effective installation and operation of these equipments. Another critical point to be considered is that the operator should search for a certain "standardization" of some parts of the subsea hardware: that means, without blocking technical innovations, it should make easier the installation and maintenance of subsea system, as regarding the aspects of spare parts and availability of qualified personnel. The basic idea the designer should have in mind when projecting very deep subsea completions is that the equipment must be as simple as possible and should have a good number of field proven parts. CRITICAL POINTS Guidelineless Completion The use of a D.P. vessel for completion work has been tested in Campos Basin from April to December 1987, when the D.P. drillship PACNORSE I performed a large number of guidelineless completion/workover jobs using standard guideline equipment (Table 1).Even though some time was lost waiting on weather to latch the tools to the tree/wellhead, one should have in mind that the ability of moving the ship precisely to a certain position proved to be quite useful in an area of strong surface and bottom currents, such as Campos Basin.