A new diverless method for deep water laying and connecting a flowline bundle linking a production well to a subsea manifold has been developed.
A specifically developed system was used and no flowline length adjustment was required "in situ".
The flowline bundle assembly is fabricated and tested on-shore, before its launching and towing. After the first phase of towing, the bundle is submerged to 30 m. The bundle is then pulled near the sea-floor with the guide rope method to the site where two base structures with acoustictransponders have been installed.
The bundle is positioned by an acoustic system. Two structures bearing a sheave for the pulling cables are lowered to the sea bottom and stabbed to the two bases respectively. All re-entries are performed by the acoustic guidelineless drilling method.
Final direct or side pulling is done by winches and heave compensators on board a drilling vessel which is successively dynamically positioned on top of each base. The side pulling is monitored by an acoustic system.
After pulling, each end of the bundle is latched to the structure. Using drill pipes the connecting modules are stabbed to the pulling structures, then a vertical connection to each end of the flowline is performed. (see fig. 1)
A sea trial of this method was successfully performed in 250 meter water depth in the Mediterranean Sea in May 1981.
Since 1970, offshore oil production has tended toward deeper and deeper seas. In 1977 particularly, several wells were drilled at water depths of more than 1000 m.
Considering this, it was necessary to design and to develop simultaneously the systems enabling to put into production the possible finds at these great depths. In order to carry out this research work, Elf Aquitaine, Total, and Institut Français du Petrole decided to found an Association. A possible scheme of development in a water depth of 1000 m was agreed upon (see fig.2). This scheme showed that many technical points remained to be solved, as for instance:
The production riser bringing the production from the sea floor to the surface.
The manifold, set up at the foot of the riser and also used for anchoring it.
The subsea production trees and their connections to the manifold by flowlines.
Taking off the production toward storage and loading facilities.
The technique contemplated in the engineering study was supposed to be applicable to flowline bundles having one 2" and one 4" diameter lines for linking two structures 1000 meters apart in 1000 meters of water.
The main problems to be solved were inherent to deep water exploration which prevents direct human intervention.
