This paper presents the design basis, procedures and equipment employed to perform offshore tests of a Vertical Connection System for flexible pipes. These tests are part of the development of a new generation of diverless and guideline less connection systems, suitable for deep water conditions.
This system is designed to connect flexible pipes to subsea equipment, especially to link Wet Christmas Trees to subsea manifolds.
The tests proved the technical feasibility of the Concept and the accomplishment of the operation either handled by drill string or wire cable. Significant feedback regarding the f1exible pipe preparation and abandonment procedures has been provided.
AS the number of deepwater, guideline less subsea equipments tends to increase, the vertical connection system advantages are addressed: simple, reliable and cost effective, providing more flexibility in the development of deep water projects with any kind of DP vessel available.
The Vertical Connection System has been developed to enable flexible pipelines to be connected to subsea equipment such as manifolds and Wet Christmas Trees (WCT) in a deep water environment where the use of guideline less (GLL) and dynamic positioning (DP) technologies is mandatory.
The project, based on the experience achieved in deepwater guideline less drilling and completion offshore Brazil, was conceived as an alternative to existing systems which use horizontal pull-in and connection of lines.
For a better understanding, the Vertical Connection System can be described as a two phase operation: the first phase consists in laying the flexible pipelines on the seafloor, abandoning the flowline termination, named "vertical connection module" (VCM), on a "temporary abandonment base" (TAB) near the equipment to which it will be connected. The second phase consists in running down a tool, picking the VCM up from the TAB, moving it over the equipment, lowering it on its receptacle and finally locking it in place. FIG.1.
Since the concept was presented on OTC 92 in paper OTC 6980 a prototype was designed and built to simulate, in a field test, the actual installation and operation conditions. The observations made during the tests gave important feedback for the improvement of both equipment and installation methods.
The operational experience obtained by testing the prototype on the development phase of the project gave enough confidence to make a pioneer offshore installation on an actual Wet Christmas Tree. This operation took place in December 1992 and was successful.
The vertical connection system was developed with three main objectives:
First, to have an alternative solution for the second end connection of flexible flow line bundles to guideline less subsea equipment. It would provide a simpler connection equipment minimize the manifold's structure with an expected cost reduction. Additionally, the time spent on the installation operation could be reduced.
Second, to avoid the simultaneous operation of the DP rig and the pipelaying vessel on first end lay-away method installations in order to gain flexibility in completion and pipelaying schedule programming. For a long time, all Wet Christmas Trees installed in deepwater off Brazil have been using the lay-away method.