Client: Confidential

Decommissioning CA and EA

Location: United Kingdom
Value Added by Xodus

Xodus’ unparalleled experience of decommissioning projects incorporating a variety of asset types, multiple fields and terminals, means we are uniquely positioned to provide expertise within this area. In addition, our integrated approach allowed for wells, subsurface, surface and environmental experts to work collaboratively with the client to assess multiple potential decommissioning programmes. Our comprehensive approach enabled our client to make informed and accountable decisions.


Xodus provided Comparative Assessment and Environmental Assessment support for the decommissioning projects for various parts of their Client’s asset. The Xodus scope included Comparative Assessment and Environmental Appraisal for 4 of the 5 Decommissioning Programmes covering decommissioning of the asset. Ownership of the assets subsequently transferred to a different client and Xodus continued the project with the new owners.


The area gas fields were discovered from 1970 onwards and production commenced in 1988. The facility comprised five bridge-linked platforms.

The Client divided the project into five decommissioning programmes for the area, based on asset partnerships, asset condition, regulatory approvals and company priorities.

The infrastructure covered by the Xodus CA scope included:

+ 6 pipelines: 3 gas export pipelines, 3 methanol import pipelines
+ 10 pipelines: 4 gas export pipelines, 4 methanol import pipelines, 2 umbilicals (control fluids)
+ 8 pipelines: 4 gas export pipelines, 4 methanol import pipelines
+ 2 pipelines: 1 gas export pipelines, 1 methanol import pipelines

The CA process followed the ‘Guidelines for CA’ that were published by Oil and Gas UK in 2015, where seven steps to the CA process were recommended. The evaluation of the decommissioning options was undertaken by qualitatively comparing the data of five criteria using a pair-wise methodology.

A formal Environmental Impact Assessment (EIA) to support a Decommissioning Programme is not explicitly required under existing UK legislation. However, the primary guidance for offshore decommissioning that was updated and published by OPRED in 2018, detailed the need for an Environmental Appraisal to be submitted in support of a Decommissioning Programme.

The study scope therefore included:

+ Preparation for and completion of a Comparative Assessment considering screened alternative decommissioning methods for the target assets,
+ Development of a detailed Environmental Appraisal report including assessments of the potential environmental and societal impact of the proposed decommissioning activities and assessments of the extent to which any impact can be mitigated and controlled to an acceptable level.

In addition to the pipelines and umbilicals covered by the CA scope, the EA scope also covered removal for the following assets:

+ 3 fixed steel wellhead platforms,
+ 2 wellhead and manifold structures,
+ 9 fixed, four-legged, steel platforms,
+ 2 fixed, eight-legged, steel platforms.


+ A small team of specialists was able to assess all aspects of the proposed late life operating philosophy and identify options for minimal manning operations;
+ Industry knowledge of decommissioning project planning and execution supported a critical review of the proposed operating philosophy;
+ High level decommissioning methodologies and assumptions were prepared to support the time and cost estimates. These provide a valuable base-case on which to develop subsequent plans.

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