KEM-48 Cumulative effects of Mining, general and in the Grijpskerk area

The overall objective of this project was to determine and clearly formulate the cumulative effects and interactions among different mining activities around the Lauwers Sea trough and the interactions among the UGS Grijpskerk, the surrounding small gas fields, and the Groningen gas field.

In particular, the research should have addressed cumulative subsidence effects, induced seismicity, the potential of leakage form wells in the area, and the expected redistribution of reservoir-aquifer pressure and formation water after the abandonment of gas fields in the Grijpskerk area.

The work was divided into two phases, A first phase with the following objective:

- literature review focussing on subsidence, induced seismicity, methane leakage, cumulative interactions among those processes, and their distribution and effects at the surface,

- obtaining input from local stakeholders and developing the Phase II research plan.

And a second phase with the following objective:

- analysing the impacts of gas extraction and gas storage in the Grijpskerk area, including their cumulative effects for both past activities and projected into the future, employing a comprehensive model-driven approach, accounting for subsidence aspects, induced seismicity, methane leakage, and other sources,

- analysing possible indirect distribution and impacts from the mining activities in terms of shallow subsidence, seismicity and the effects on groundwater and methane leakage.

DETAILED RESEARCH QUESTION

The work was divided into two phases:

The research in Phase I relies on a structured literature review and a feasibility assessment of innovative methodologies. The literature study is comprehensive and addresses: subsidence (natural and anthropogenic), induced seismicity, methane leakage, cumulative and interactive effects, monitoring techniques, and modelling approaches. The study applies clearly defined classification schemes (e.g., shallow vs. deep subsidence), integrates empirical data (e.g., NAP elevation benchmarks), and discusses a variety of modelling approaches (poroelastic, geotechnical, semi-analytical, etc.). In the feasibility study, the novel DELTA method is introduced, which utilizes raw NAP data for subsidence analysis with improved precision. This innovation strengthens the methodological quality and is a promising foundation for Phase II.

PROJECT REPORT PHASE I

The findings of Phase I provide a systematic synthesis of: the magnitudes and causes of subsidence and seismicity across different depths and origins, the significance of well integrity and fault structures for methane leakage, the mechanisms and spatial extents of interaction zones between mining activities. The results are well-structured, extensively referenced, and contextualized within national research (e.g., DeepNL and previous KEM projects). The report integrates scientific insights with stakeholder concerns, particularly in relation to the Grijpskerk region.

The methodological framework of Phase II is a system-oriented integration of monitoring, modeling, and interpretation tools aimed at assessing cumulative effects in the Grijpskerk area. The following studies have been performed:

- Geodetic analysis: high-resolution evaluation of subsidence and surface deformation using raw NAP data and the DELTA method developed in Phase I.

- Reservoir compaction modeling: modeling of gas extraction

–induced deformation and subsidence was performed using a simple linear-elastic compaction model. Results were compared against field data.

- Seismicity assessment: probabilistic and deterministic evaluation of induced earthquakes in relation to gas field operations, with considerations of magnitude thresholds and source mechanisms.

- Leakage pathway identification: conceptual assessment of pressure migration and well integrity, supplemented by fault and wellbore data.

- Interaction zone mapping: The interactions between the Grijpskerk UGS, nearby fields (e.g. Pieterzijl and Kommerzijl), and the Groningen gas field are evaluated by comparing their respective pressure, subsidence, and stress footprints, and by mapping zones of overlap and influence. Innovative use of lateral and vertical distance buffers to infer potential coupling between subsurface activities.

PROJECT REPORT PHASE II

The scientific findings presented are well-structured and cover:

- Quantification of compaction and deep subsidence in the Grijpskerk area from multiple gas fields, with spatial footprints of subsidence modeled over time.

- Quantification of compaction and deep subsidence from Grijpskerk UGS and its radius of influence.

- Quantification of shallow subsidence rate, also based on InSAR data.

- Mapping of induced seismicity probabilities and evaluation of existing data on earthquakes and vibrations.

- Interpretation of uncertainties related to input parameters (e.g., InSAR observations, shallow subsurface maps, compaction coefficients, boundary conditions, fault transmissivity), modelling results, and water management practices.

Recommendations for risk mitigation and monitoring strategies, tailored to different stakeholder concerns (e.g., damage to buildings, groundwater salinization, public perception).

The project was evaluated by the KEM sceintific expert panel.

PROJECT EVALUATION

The project deliverables are considered to be clearly presented, scientifically robust, and directly tied to the project objectives. The inclusion of an English executive summary, structured annexes, and auxiliary documents enhance accessibility and traceability. The quality of analysis is high: each module (subsidence, seismicity, leakage) follows a consistent problem-definition–method–result–conclusion structure, ensuring traceability and scientific clarity.

The study shows that gas extraction and storage activities around Grijpskerk and the Lauwers Sea trough have caused only small and predictable effects. All observed earthquakes can be attributed to gas production from Groningen field or from small fields in the project area (Kommerzijl, Munnekezijl, and Grijpskerk). There are no indications of induced seismicity due to other gas-related subsurface operations (drilling, hydraulic stimulation, hydraulic fracturing, and water injection). The risk of methane leakage is considered to be very low. Different mining projects in the area also do not appear to reinforce each other’s impacts.

The study in this project had a generic nature. For each specific site, one must carry out detailed studies and employ integrated assessment methods that look at deep subsidence, leakage, pressure development, and shallow subsidence effects together rather than separately. In preparation for such studies, even small effects must be monitored carefully and locally, using tools such as InSAR, GNSS and pressure monitoring.

These insights support the development of smarter mining policies and monitoring systems, with more transparency, better coordination between operators, and attention to site-specific risks—especially when fields are closed or used for other purposes such as (gas) storage. In short: while the current situation is stable, one must continuously improve the way that mining effects are assessed and monitored to stay ahead of future challenges.