Decommissioning Scope and Practice Southern North Sea (SNS): Subsea The following summarises the outputs of workshops held in Q3/Q4 2016, exploring the scope and practices of several SNS Operators with subsea aspects of decommissioning The workshops focussed on scope and practices covered by approved Decommissioning Programmes The scope and practices listed, and the drivers leading to their adoption, are examples of approaches taken This is not a comprehensive list of all options there may be other options which are superior to those listed these do not necessarily represent the best, or good, practice A fuller range of options will, in many cases emerge, as decommissioning experience develops and more Operators contribute to this body of knowledge Likewise, the most competitive options will likely become clear from the statistics of the options adopted by Operators in coming years. 18 September 2018

What are the targets to engineer the solution to? Execution Examples: Process description Screening / Ranking Situation/Issue Example Objectives Example Options Relative Cost Outcome Why is this activity being undertaken? A clear & justified objectives statement will align with cost-effective option selection What is the decommissioning starting point, and the issue ? Typically this is a fixed situation But it may also be a choice Selected option What are the costs of the options? Safety The options will screen differently when comparatively assessed, and a compliant yet cost-effective option can be selected What are the different ways that the objectives & associated metrics can be practicably achieved? Environmental Medium Lowest Technical Highest Low High Societal Metrics/Targets Low, but risk of high Economic What are the targets to engineer the solution to? Metrics should be challenged to test how unique/non-unique they are, & whether other acceptable metrics open-up more cost effective solutions Options objectively compared using the Comparative Assessment framework in line with BEIS-ODU guidance if required / proportionate

Execution Examples: Pipeline Decom Preparation Screening / Ranking Situation/Issue Example Objectives Example Options Relative Cost Outcome Oil/gas removal to remove hazard Oil Pipeline - Known contents Oil/gas removal to allow intervention Selected option Oil Pipeline - Unknown contents Reduce toxin entry into food chain What are the costs of the options? Pig + Water Flush + monitor/measure Safety Gas Pipeline - Known contents Minimise environmental impact Medium Lowest Environmental Pig + Water Flush Technical Gas Pipeline - Unknown contents Highest Water Flush Low High Societal Low, but risk of high Multiphase Pipeline Others Economic Injection-water pipe Metrics/Targets Chemicals flowline Hydrocarbons in water Defined methodology Options objectively compared using the Comparative Assessment framework in line with BEIS-ODU guidance if required / proportionate Reasonable endeavours

Execution Examples: Mattress Decommissioning Screening / Ranking Situation/Issue Example Objectives Example Options Relative Cost Outcome Minimise hazards to offshore personnel Minimise hazards to other users of the sea Selected option Mattress with High structural integrity Minimise hazards to the environment Total recovery of mattresses What are the costs of the options? Safety Environmental Mattress with Low structural integrity Partial recovery of mattresses Medium Lowest Technical Buried Mattress No recovery of mattresses Highest Low High Societal Unburied Mattress Rock dump over mattresses Low, but risk of high Economic Mixed Burial Mattress Metrics/Targets Minimise snagging hazard Options objectively compared using the Comparative Assessment framework in line with BEIS-ODU guidance if required / proportionate Risks are ALARP

Execution Examples: Pipeline Decommissioning Screening / Ranking Situation/Issue Example Objectives Example Options Relative Cost Outcome Minimise hazards to offshore personnel Large Diameter Pipeline ≥ 16” Minimise hazards to other users of the sea Small Diameter Pipeline < 16” Selected option Minimise hazards to the environment Total recovery of pipelines What are the costs of the options? Safety Buried Pipeline Partial recovery of pipelines Lowest Environmental Medium Unburied Pipeline Technical Highest Mixed Burial Pipeline No recovery of pipelines Low High Societal Rock dump over pipelines Flexible Pipeline Low, but risk of high Economic Rigid Pipeline Metrics/Targets Bundle Pipeline Minimise snagging hazard Umbilical Options objectively compared using the Comparative Assessment framework in line with BEIS-ODU guidance if required / proportionate Risks are ALARP

Execution Examples: Subsea Equipment Decommissioning Screening / Ranking Situation/Issue Example Objectives Example Options Relative Cost Outcome Minimise hazards to other users of the sea Minimise hazards to the environment Selected option Total recovery of subsea equipment What are the costs of the options? Safety Equipment without an over-trawlable structure Partial recovery of subsea equipment Environmental Medium Lowest Technical No recovery of subsea equipment Highest Low Equipment with an over-trawlable structure High Societal Low, but risk of high Rock dump over subsea equipment Economic Metrics/Targets Snagging hazards Options objectively compared using the Comparative Assessment framework in line with BEIS-ODU guidance if required / proportionate

Execution Examples: Post-Decommissioning Monitoring Screening / Ranking Situation/Issue Example Objectives Example Options Relative Cost Outcome Confirm there are no hazards to other users of the sea Confirm there are no hazards to the environment Selected option High Frequency Monitoring What are the costs of the options? Safety Environmental As left situation, post completion of decommissioning Medium Frequency Monitoring Medium Lowest Technical Highest Metrics/Targets Low Frequency Monitoring Low As left situation, post completion of previous surveys High Societal Low, but risk of high Economic Critical spans No Monitoring Exposures New snagging hazards Pipeline and mattress stability Options objectively compared using the Comparative Assessment framework in line with BEIS-ODU guidance if required / proportionate Identify any leaks