Abandonment of offshore oil and gas fields

Over the coming decades, a substantial number of oil and gas wells in the Danish sector of the North Sea will have to be plugged and abandoned. This abandonment work will not only be cost and time consuming; it may also have a large impact on the environment both in the short and long term. The Centre has started a new research programme with a focus on the specific challenges in the Danish North Sea with the aim of ‘robust and cost effective abandonment for short and long term environmental protection’.

The Gorm platform in the North Sea. Photo: TotalEnergies

The abandonment research programme has been divided into six prototypes both focusing on well abandonment and environmental abandonment. 

1. Temporary Pumpable Reservoir Isolation

Prior to the well abandonment, the wells must be temporarily isolated for pre-abandonment interventions. This is normally done using mechanical plugs. However, a significant number of the wells in the Danish North Sea suffer from scale build-up preventing the installation of mechanical barriers. Therefore, a lot of time and money are spent on scale removal before the initiation of abandonment operations.   

This prototype focuses on developing pumpable barriers to avoid scale removal. 

  • PolymerInject: Development of polymer which can be injected into the reservoir to seal chalk reservoirs.
  • Modular Polymer Plug: Development of polymer-based plug for tubing isolation. 
  • Reservoir Clugging: Investigation of precipitation for reservoir isolation.
  • SCPTracer: Develop the ability to identify the origin of sustain casing pressure build-ups. 

The materials will be developed specifically for the conditions and operations in the Danish North Sea. 

2. Combination of Scale and Cement as Well Barrier

The oil and gas industry aims to perform as many rigless abandonment operations as possible to reduce the cost and minimize the environmental impact. To achieve this, the tubing will have to be left in the well, and the well barriers are to be installed around the tubing. This means that the scale in the tubing must be removed before the barrier installation. The hypothesis for this prototype is that the cement barrier can be set inside the scale and the scale can become part of the final barrier. 

  • Scale as part of a well barrier: Two short feasibility studies have been finalised indicating that the concept is possible. The two research groups will jointly work towards proving the concept of setting cement barriers in scale and at the same time strengthening the downhole scale. Scale is generated inside the tubing over the lifetime of the well and scale is very expensive to remove and store onshore. Consequently, this technology will leave the scale in the well and be used as part of the well barrier.
  • Cement degradation over time: This project is working on understanding what happens in abandonment cement over time, and will suggest cement recipe improvements based on the behavior over a period. 

3. Shallow Permeable Zones

Several permeable zones above the oil and gas-producing reservoirs can have flow potential, so they need to be abandoned. The objective of this research is to create an understanding of the flow potential, specifically in the Diatomite formation. The focus is on achieving an improved understanding of permeability in the Diatomite and the regional Diatomite stratigraphy and modeling the flow potential. The knowledge generated in this project is intended to help decide where the abandonment barriers need to be installed.

4. Environmental Baseline of cods around Offshore Structures

When an oil and gas field is decommissioned, the installations will be removed from the seabed and up. Currently, it is not well understood if these structures form a crucial habitat for marine species. Therefore, it is important to clarify this before removing the installations. This project aims at understanding the importance of the structures for the cod communities both with respect to the number of individual cods and the way they use the structures. The project includes offshore data collections, which are planned for the summer 2023 with a small follow-up campaign in 2024.

5. Environmental Baseline for Natural Hydrocarbon Seepage 

When all the oil and gas wells in a field have been abandoned, there are likely to be requirements in place for the monitoring of potential methane leaks. However, where does the methane come from? Oil and gas wells are often drilled in areas with natural hydrocarbon seepage. It is therefore difficult to say if measured methane is coming from a potential well leak or natural seepage. This project aims to establish a baseline for the natural hydrocarbon seepage based on geophysical data and shallow cores collected around Gorm and Valdemar platforms, and in addition in areas away from the oil and gas production.

6. Surveillance of Abandoned Wells

The aim of this prototype is to develop a sensor that can detect and measure potential future methane leaks at the seabed. This prototype is key to being able to fulfill the expected monitoring requirements around abandoned oil and gas fields.


Charlotte Nørgaard Larsen

Charlotte Nørgaard Larsen Programme Manager Danish Offshore Technology Centre Mobile: +45 93511536