KEM-16a Subsidence hazard and risk due to gas/salt production (subsidence HRA)

As a follow-up to recommendations from the Knowledge Program on Effects of Mining (KEM 3a project: Mining effect hazard and risk assessment models Toolbox), the objective is to develop a generic method for evaluating subsidence due to mining activities and other subsidence mechanisms relevant onshore in the Netherlands.

Currently (2020), practical subsidence questions posed by various authorities on the accumulation of causes of subsidence cannot all be answered with one integrated instrument but require a complex toolbox with working methods for specific issues. The available methods can vary from integration of models and formal inversion with subsidence data to decoupled, step-by-step deployment of a selection of models, from deep to shallow. A suitable approach depends, among other things, on whether it concerns reconstruction or forecasts for the future.

The objective is to research in two to three pilots including multiple subsidence causes, how current subsidence hazard models available in The Netherlands can be integrated and improved to include to become a high-quality generic tool for onshore subsidence hazard analysis, which can later be extended to full subsidence hazard and risk instrument.

FULL RESEARCH REQUEST

The results of the work in the KEM-16a project have been reported in four documents:

Mining-induced subsidence and water level management (Deltares 11205981-003-BGS-0001), Groundwater table lowering due to surface water lowering (Deltares 11205981-004-BGS-0001) on shllow subsidence proceses.

Toolbox subsidence: Discriminating subsidence contributions from multiple mining activities; case study Diever, Vinkega and Eesveen area (TNO2022_R11963) and The PySub Subsidence Model Framework: Technical Reference (TNO2022_R11962) on deep subsidence processes.

In consultation with three northern water boards, two case studies were selected and conducted related to mining-induced subsidence and water level management effects. Case 1, Nedmag-Veendam, concerns the historic effects of subsidence due to salt mining. Case 2 is a hypothetical case that explores deep subsidence effects in an area, between Delfzijl and the city of Groningen.

For the simulations, the open source tool Atlantis, which previously was developed for shallow subsidence, was extended to also include coupling with a newly developed deep subsidence modelling tool (PySub). PySub code has been made publicy available by TNO as open source software and can be found using this link.

The reported features of the developed tools are that (i) the indirect effects of deep subsidence and surface water and groundwater management decisions can be quantified separately, and (ii) complex time-varying scenarios can be efficiently analyzed. The two case studies that were conducted in phase 1 thus far were insufficient to support generic conclusions regarding the relative contributions of shallow subsidence in the effect of deep subsidence on freeboard change.

The KEM scientific expert panel has reviewed the KEM-16a project.

KEM PROJECT EVALUATION

The amount of work performed in this project is substantial. The tools developed in this project are unique, and can be considered to be “state of the art”. The various project reports have been well written and are easy to read. The project has led to the extension of the open source code Atlantis, enabling modeling of the combined effects of deep and shallow subsidence, and the development of a computational modeling tool called the “PySub Subsidence Model”, which models and visualizes the combined effect of different mining activities on deep subsidence. The tools represent a major advance in the state of the art in subsidence modeling of the effect of mining in the Netherlands. However, further experience in the use of the tools will be needed before their accuracy and usefulness can be confidently assessed.

As has been admitted by the project researchers, the results obtained thus far related to the effects on shallow subsidence of deep subsidence must be considered to be a work in progress, and further experience with using the Atlantis tool for this purpose is needed before its usefulness can be definitively assessed. A KEM-16 Phase 2 project (KEM-16b) has started in 2023.