Subsea-Pipeline Intervention With Coiled Tubing From a Supply Vessel

Abstract

Abstract Coiled tubing (CT) pipe has been successfully used in the past to clean and abandon in situ subsea pipelines in offshore areas where conventional industrial approaches (i.e., pigging, flushing or suction) were not feasible. The technique of using CT has been explored before and the subject has been covered in previous SPE papers1. The basis of the previous work relies on the CT pipe's strength to be pushed through long, horizontal lines and its ability to convey tools and fluids at once. One of the main limitations, however, in using CT for pipeline interventions in offshore environments as opposed to the traditional methods is the amount of equipment required on board. In most cases, deck space, loading constraints and operational factors such us seabed, heave, or current direction, fixed have posed significant challenges. These challenges have been addressed in some specific cases for production platforms, jack-up boats, or dynamically positioned (DP) monohull vessels. However, traditional coiled tubing intervention will not always provide a feasible solution. A particular operationally challenged subsea pipeline intervention exists in the Congo delta. The pipeline, which linked two production platforms, had been plugged with organic deposits and two pigs from an initial cleanup attempt in November 2004. Subsequent conventional trials failed to break through these obstructions, so CT was proposed as a feasible alternative. The platform's deck space and crane load capacity, 4-knot sea currents rich in alluviums and products from the Congo river, and 46-ft seabed that used either jack-up boats or DP vessels not an option. This paper discusses the unique solution developed to address the operational and technical challenges of this difficult environment