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Cavern convergence and subsidence: assessment of the Heiligerlee cavern field

Motivation of the study

To support their supervision on cavern closure at the Heiligerlee salt production location, State Supervision of Mines (Dutch abbreviation: SodM) requires additional knowledge and understanding on factors and specific closure schemes controlling the progress of long-term subsidence. The insights can have implications for cavern closure at other locations as well and provides directions on the remaining key research questions to be solved.

Research question

At the request of SodM, TNO-AGE has analysed post-closure subsidence forecasts at the Heiligerlee salt production location (northeast Netherlands), considering different pressure conditions from halmostatic to 90% lithostatic pressure. The assessment follows the assumption that the 12 caverns are immediately and simultaneously put on pressure control via the wells. The specific study objectives are to assess:
 

• The influence of post-closure pressure regimes on the expected rate and progression of cavern convergence and subsidence using a range between 90% lithostatic pressure1 and halmostatic pressure;
• The development of expected total subsidence at the deepest point of the subsidence bowl at the Heiligerlee location within a 50-year forecast window, including insights and limitations to assess the subsidence on long-term time scales.
• The key uncertainties and most important sensitivities, other than deterministic post-closure pressure scenarios, that influence these subsidence predictions.