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Well Plugging and Abandonment

Field decommissioning may be a significant economic burden for operators, especially in the case where its cost was not incorporated in a full field development case.

Sealing well paths in an effective and environmentaly friendly way at the end of field life

Figure 1 shows some projections of decommissioning expenditures toward 2030, for the UK Continental Shelf. It is possible to see how these cumulative costs are above 1 billion GBP each year.

Figure 1.Decommissioning expenditure forecast for the UK Continental Shelf (Oil and Gas UK 2021).

Isamgeo can offer to its customers a tailor-made strategy for well plugging and abandonment that would seal any potential leak path, for residual reservoir fluids or for any other overburden formation fluids, over a long-term perspective (50 – 100 yrs).

 

From an operational point of view, several plugs are created along the abandoned well, see Figure 2. 

Figure 2. Production well schematic, before and after plugging and abandonment (Vrålstad et al. 2019). 

Isamgeo’s strategy for efficient and environmentally friendly plugging and abandonment would consider several crucial factors that otherwise would drastically reduce the reliability of plugs:

 

  • The in-situ state of stress at field abandonment may have changed sensibly due to production operations, with a stress path that is specific to each field, and that requires thorough investigation. A stress path example is given in this page. The history matched dynamic simulation must correctly capture the evolution of the reservoir pressure until well abandonment.   
  • The potential for fault re-activation that would induce instability and disintegration of the cement plugs;
  • The effects of temperature and chemical alterations at the cement / fluid and rock / cement interfaces.

Figure 3. Field stress path. It shows the effect of hydrocarbon production and fluids injection on reservoir pressure (Aruffo et al. 2014).

These issues would be addressed, for each distinct field case, through geomechanical modelling at different scales:

 

  • A full-field hydro-mechanic modelling of the reservoir, side-burden and over-burden over a 50–100 yrs period. This model is needed to constrain the stress evolution and identify the most likely locations that may be subject to fault re-activation and/or plugs failure;
  • A series of small-scale models that will incorporate stress effects, as well as temperature and chemical reactions. Different plugging strategies (type, location and thickness of the cement) are typically simulated and tested.

 

Isamgeo’s combined geomechanical modelling at different scales will support the design of the safest and the most cost-effective plugging and abandonment operations.