Abstract
The storage cavern field at Epe has been brined out of a salt deposit belonging to the lower Rhine salt flat, which extends under the surface of the North German lowlands and part of the Netherlands. Cavern convergence and operational pressure changes cause surface displacements that have been studied for this work with the help of SAR interferometry (InSAR) using distributed and persistent scatterers. Vertical and East-West movements have been determined based on Sentinel-1 data from ascending and descending orbit. Simple geophysical modeling is used to support InSAR processing and helps to interpret the observations. In particular, an approach is presented that allows to relate the deposit pressures with the observed surface displacements. Seasonal movements occurring over a fen situated over the western part of the storage site further complicate the analysis. Findings are validated with ground truth from levelling and groundwater level measurements.
Highlights
The storage cavern field at Epe has been brined out of a salt deposit belonging to the lower Rhine salt flat, which extends under the surface of the North German lowlands and part of the Netherlands
We demonstrate below that the seasonal movements are presumably caused by groundwater level changes
The residual phase comprises non-compensated errors and the not modelled signal. The latter presumably gives a partial explanation for the high values of root mean square (RMS) over the fen, because the actual highly irregular seasonal signal supposedly deviates from its model
Summary
The storage cavern field at Epe has been brined out of a salt deposit belonging to the lower Rhine salt flat, which extends under the surface of the North German lowlands and part of the Netherlands. Near Epe the deposit has a thickness between 200 and 400 m and the top of the salt layer (abbreviated as top salt throughout the text) lies in an average depth of 1000 m. The currently 114 caverns are used for brine production and for storage of natural gas, helium and crude oil by in total 8 companies, which follow independent operating strategies. Mining-caused effects are monitored regularly with levelling, ground water measurements, and other techniques. For our study the potential of SAR interferometry (InSAR) for monitoring nonlinear movements over the storage site has been investigated
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