Subsea Pipelines and Flowlines Decommissioning: What We Should Know for a Rational Approach

Abstract

Offshore and subsea decommissioning will increase in the next five years or so as many producing fields are matured and cease production while the oil price continues to remain low. This emphasizes the need for a thorough decommissioning plan to ensure a safe and technically feasible solution while it is economically viable and safeguards the environment. Offshore and subsea decommissioning is commonly considered on a case-by-case basis using the Comparative Assessment (CA) process in which the best decommissioning solution is obtained. Health, Safety and Environmental (HSE) considerations are always paramount in any decommissioning process. The aim is to significantly reduce the long term risks to other benefactors of the sea while the associated short term risks to those responsible for decommissioning operations are minimized. A major part of any decommissioning project is subsea pipelines decommissioning (by “pipelines”, it is meant to include flowlines, trunklines and flexible too). There are a number of techniques available for decommissioning of subsea pipelines ranging from preservation for potential future use to full recovery or leaving in-situ. However, each subsea pipeline decommissioning technique should be considered on its own merit. Selection of each decommissioning technique depends on many parameters, inter alia, size of pipeline, type of pipeline (e.g. single pipe, pipe-in-pipe, piggyback), type of conveying fluid, operational environment (location), production history, Inspection, Repair and Maintenance (IRM) records, HSE considerations, connection to other facilities, technical feasibility (including potential use of advanced technologies), regulatory authorities requirements and socio-economic considerations. This paper will look at specifics of subsea pipelines decommissioning. It will examine the procedures to be undertaken from desk top activities (e.g. planning and CA) up to operational activities (e.g. pigging, flushing, cleaning, removal or leaving in-situ). Different scenarios are discussed and potential advantages and disadvantages of each scenario are presented. In addition, a guide is proposed for future pipelines decommissioning projects to follow a rational approach.

An Assessment of Environmental Impact on Offshore Decommissioning of Oil and Gas Pipelines

“…Some fishes might move down to the platform or seek a new inshore shallow habitat that will increase competition for resources [10]. In the end, removing the buried pipeline from the seabed may not be feasible since it has a more detrimental effect on the environment and requires expensive technology or equipment [39]. Not only will the seabed be disturbed, but the habitat will also be destroyed.…”

“…The uncertainties regarding the timing of decommissioning works creates difficulties in establishing an effective marketplace for service, which was found to be the limiting factor to investing in innovative cost-saving technologies for decommissioning [60]. As more oil and gas platforms will soon come to their lifespan, a lot of decommissioning works will need to be executed [39], as most of the regulation requires them to be removed at the end of their service life. Therefore, to achieve successful decommissioning of deep pipelines, the industry needs to develop an improved, safe, environmentally friendly, and cost-effective decommissioning strategy [20].…”

Guideline for the Decommissioning/Abandonment of Subsea Pipelines

“…Decommissioning a pipeline refers to disconnecting a pipeline from all sources of process fluid, removing process fluid from the pipeline, and leaving the pipeline in a safe state for potential repair, intervention, future re-commissioning, or permanent removal from service [8][9][10][11][12][13][14][15][16][17][18][19]. Please refer to Appendix A for the definitions and terminologies used in the decommissioning industry.…”