The final report was submitted in November 2019, consisting of a synthetis report.
RESEARCH PROJECT FINAL REPORT
In addition, 4 work package reports were delivered. Three reports on studies at the micro-, cavern respective dome scale. See: Micro-scale REPORT, Cavern-scale REPORT and Dome-scale REPORT. One report addresses practical measure:
REPORT on Practical Measures
The research question was approached at three different scales: the scale of the grains in the salt formation (micro-scale), the cavern scale, and the salt dome scale. A detailed individual report was prepared for each of the three components of the research, along with a brief report that summarized the findings and conclusions.
The reports on (1) micro-scale, (2) cavern-scale and (3) dome-scale include each:
1. Literature review of already available knowledge on the mechanisms of brine leakage (permeation/hydraulic fracturing/other) when the brine pressure reaches or exceeds the local minimum stress. Include case studies if available. With the micro-scale processes being the most important.
2. Criteria for determining when which leakage mechanism (permeation/hydraulic fracturing/other) is dominant and in whih cases it cannot be determined. Criteria should be a function of salt properties (mechanical, chemical, grain size, heterogeneities), brine pressure, (local minimum) stress and temperature.
3. Report on state of the art and scope for improvement of the salt mining effect modelling approaches and tools for predicting the short (operational) and long term (post abandonment) behaviour of typical caverns in The Netherlands under different cavern pressure strategies, including permeation, fracturing and brine leakage, and salt collapse effects.
The project has resulted in better insight into the potential causes and their role in leakage at microscale, cavern and scales) of salt caverns in The Netherlands. It was concluded that for closed caverns deeper than 1000 meters leakage risks may exist.
Further, a catalogue was produced of required measures by operators and owners of abandoned caverns for different cavern typologies to prohibit any uncontrolled cavern leakage and thereby reduce hydrogeological risks in aquifers and geotechnical risks at the surface.
The potential of catastrophic leakage events can be avoided by either (a) delaying the final plugging of the cavern until closure has occurred (in those cases in which the closure rate is high enough for this to be feasible), or periodically venting brine from the cavern after it has been abandoned, to avoid a pressure build-up that might be large enough to cause fracturing or other types of localised leakage
