Throughout the months of November and December 2023, Prism Energy oversaw a complex Pipeline Pigging scope in the North Sea. The isolation tool was launched from a facility run by one operator but pigged to a subsea set location within the boundary of a second operator.
The project was centred around a double block & monitor (DBM) isolation tool pigging run, to facilitate a subsea reconfiguration of the pipeline in Q2 2024.
Prism Energy’s role was to manage the supply and hire of an isolation tool and temporary pumping spread to provide a suitable double block & monitor (DBM) isolation as well as ensuring the launch facility was prepared for the launch. Prism project managers were tasked by each operator to oversee the scope.
The isolation tool was to be launched, from operator 1s facility and pigged 7.5km to a subsea set location. The isolation tool was tracked to set location and set by a team onboard a Diving support vessel (DSV). The isolation tool is to remain in place until the pipeline is cut and reconfigured subsea in Q2 2024, where operator 1 will be disconnected from the system.
The scope included the management of the isolation tool provider, the temporary pumping spread provider, Lessons Learned session, facilitation of HAZID & HAZOP sessions, attending Factory Acceptance Tests (FAT), reviewing vendor documentation, and writing the overarching launching, and retrieval, operating procedure.
Operator 1 had not used the pipeline for gas export for a number of years, since a new gas export route was brought online, this offered up specific challenges in reinstating the system for pigging operations.
The pig run offered a significant challenge due to the distance and duration of the pigging operations as well as the negotiation of topside features. The pig train consisted of 2x high seal pigs and the isolation tool, each pig separated by a slug of MEG (mono ethyl glycol/anti hydrate solution). This configuration offered an effective barrier between the pipeline gas inventory and the pigging motive fluid of seawater/glycol mix which also prevented the formation of hydrates.
The set location required a vessel to be on location for the setting of the isolation tool. As the project was executed in winter the project managers must ensure a suitable weather window for the pigging operations.
The success of the project will enable operator 1 to bring new wells online following the removal of the Gas export line infrastructure. Operator 2 will follow up with phase 2 of the project which involves the installation of a subsea pig launcher ensuring their capability for future pigging operations.
