Miniaturized Coiled-Tubing System Reduces Costs During Pipeline Decommissioning

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 175487, “Cost-Reducing Pipeline-Decommissioning Technology,” by Hugh MacKenzie and Callum Jones, Paradigm Flow Services, prepared for the 2015 SPE Offshore Europe Conference and Exhibition, Aberdeen, 8–11 September. The paper has not been peer reviewed. This paper presents the challenges and obstacles faced in the use of a new technology for the plugging and deoiling of sections of unpiggable flowlines before decommissioning. The solution used an ultralightweight, miniaturized coiled-tubing system that was deployable from the platform lower decks with minimal laydown area required. The system had the ability to traverse multiple bends, deoil the line, and deliver an expandable cement to plug the pipeline in a single operation. Introduction First production in the Murchison field began in 1980, and the field has now reached the end of its life. As part of the decommissioning project, one of the subsea wells was seen to be still connected to the Murchison platform by two flowlines contained within a subsea bundle (PL123), with these flowlines having 4-in. outer diameters. These lines were installed to provide early production for the first year until all the infrastructure was put in place. The control lines and pressure-monitoring system had been disconnected at the platform sometime in the past (Fig. 1). The bundle was inspected on the platform, and a hot tap was performed to identify any pressure in the lines and to identify the line contents. It was found that one of the two flowlines contained crude at a pressure of 122 bar. The pressure was reduced to zero, and the bleed line was closed with a gauge installed to monitor the pressure. It was noted that the pressure increased slowly over time. To continue with the decommissioning of the platform before the plugging and abandonment of the subsea well (211/19-2), PL123 had to be flushed of contents and a barrier had to be installed between the subsea well and the Murchison platform.