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Assured Solutions for Well Decommissioning


We are the leading provider of subsurface designs for well abandonment.

Since 2018 Stag has been undertaking Basis of Abandonment Design work to optimize and reduce the number of plugs required for the safe abandonment of oil, gas and condensate wells worldwide.

Our Well Decommissioning Framework is a modular workflow which cost-effectively resolves the optimum Subsurface Basis of Abandonment Design for any P&A project, from the permanent abandonment of a single suspended well to the assured decommissioning of large fields or multi-field clusters.


A Stag Subsurface Basis of Abandonment Design will guide a safe, cost-effective strategy with all risk identified, mitigated, and turned to new opportunity.


Our work is always compliant with the regulatory requirements of the licensee, the operator, the well examiner, and all national authorities. 

Working with us has consistently resulted in shortened P50 execution expectations, reduced risk and liability, and greater cost efficiency for all our clients.

Find out how our Well Decommisioning Framework can kick-start your P&A project below.


Since 2018










Introducing our Well Decommissioning Framework.

Our Well Decommissioning Framework comprises five discrete modules which can be commissioned as individual studies or in any appropriate combination. Different P&A projects have different challenges, and this means that the right workscope for a Basis of Subsurface Design will vary from project to project.​​

Barrier Location Models

A Barrier Location Model is the most cost-effective way to meet all the requirements for subsurface preparation for P&A as detailed in the OGUK Well Abandonment Guidelines, especially on fields with a large number of wells. Rapidly returning robust results, a Barrier Location Model will:

  • Resolve the distribution of permeable rock units in the overburden, identifying all intermediate zones of Flow Potential;

  • Estimate fluid type and pressure in the zones of Flow Potential;

  • Estimate rock strength throughout the overburden and identify candidate caprocks against which a barrier may be set;

  • Identify opportunities for grouping zones of Flow Potential with a common pressure regime beneath common barriers.


Geological Engineering Models (GEM)

Our Geological Engineering Model (GEM) has proven itself the best-in-class single-well solution for P&A. Ideally suited to decommissioning fields produced by a single or limited number of wells, or as a detailed study of individual wells within a Barrier Location Model which have more complex engineering challenges, the GEM builds on the Barrier Location Model to:

  • Precisely resolve the shallowest possible position at which permanent barriers can safely be placed, using a bespoke pore pressure, fluid gradient and rock strength model tailored to the individual well;

  • Illustrate the P&A stratigraphy of the well, with Flow Zones, Permeable Zones and Isolation Windows plotted and defined;

  • Describe the well construction in a geological context with a detailed well schematic drawn to scale alongside  the geology and pore pressure model;

  • Illustrate the distribution and quality of primary cement (as determined either by the operator or by Stag) behind the casings.

Annular Integrity Evaluation

Our Annular Integrity Evaluation is a cement job evaluation tailored for P&A purposes rather than generic production isolation. Suitable for the reassesment of any historic cement job, our evaluation:

  • Requires over 100 technical inputs to resolve a pass/fail of 18 Key Criteria;

  • Breaks out five separate elements for analysis: Open Hole Conditions at Section TD, Casing Run Job, Preflush Job, Cement Job, and Post Completions history (sustained casing pressures, evidence of squeeze or collapse, and junk or damage).

  • Recalculates the Theoretical Top of Cement (TTOC) and compares the result to previous estimates with a variance and confidence calculation;

  • Provides results which can be illustrated on the GEM.


Bond Log Verification

Stag provides full services for Cement Bond Log interpretation and verification as part of our Well Decom Framework. We provide:

  • Interpretation of Cement quality and quantity behind casing from any vintage of Bond Log, including historic CBL/VDL run at the time of completion and new segmented or ultrasonic measurements made to support P&A campaigns;

  • Interpretation of cement density and porosity from ultrasonic tools in order to define cumulative lengths of cement with sufficient impermeability to support permanent barriers;

  • Realtime support during operations, including remote supervision and on-site witnessing;

  • Full Decision Support services for optimising barrier placement post-run.

Crossflow Qualification

When an optimal barrier strategy includes grouping multiple zones of flow beneath a common barrier in one or more wells, clients often wish to investigate the consequences of commingling subsurface fluids in order to ensure there is no possibility of loss of containment via faults or neighbouring non-operated wells. This is particularly important when hydrocarbons are allowed to commingle with previously wet rocks beneath a new and higher cap rock.


In order to de-risk crossflow, we offer specialist Structural Analysis, Fault Seal Analysis and Cap Rock Qualification services which build on the stratigraphic interpretations and pore pressure and rock strength models made in our Barrier Location or GEM models.


Our Projects

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