Saltwater injection into a fractured aquifer: A density-coupled mass-transport model

摘要

The Werra-Kali potash mining region has a mining history for more than 90 years. The mining region is situated both in the Free State of Thuringia and the federal state of Hesse, Germany. Since 1925, high saline waters of potash productions have been injected into a confined, deep aquifer of the Permian Zechstein formation (carbonate rock aquifer).The carbonate rock aquifer is a regional aquifer with extensive natural variations of salinity of geogenic origin, ranging from fresh to saline waters. Its overburden consist of the formation series "Obere Letten" of upper Permian, the Triassic Buntsandstein and Muschelkalk formations. The formation series "Obere Letten" consists of clay- or siltstone and hydraulically separates the carbonate rock aquifer and the Buntsandstein aquifers. The Buntsandstein is subdivided in the lower, middle and upper Buntsandstein, where the lower Buntsandstein is a regional aquifer and the middle Buntsandstein occurs partly as perched aquifer. The upper Buntsandstein is an aquitard and hydraulically separates the underlying middle Buntsandstein from the overburden Muschelkalk. Muschelkalk occurs in the southern part of the region, partly as perched aquifer. Finally, the quaternary sediments occur in river valleys and form local shallow aquifers.Groundwater levels, salinity, and water levels in the nearby river have been monitored for several decades. The aim of the project was, based on available data and results of geological works and mining investigations, to develop a numerical groundwater model capable of simulating the impact of the injection regime of the past 90 years on regional flow patterns and solute transport underground and identifying possible relations between saltwater injections and the non-point (diffuse) saltwater inflows into the nearby river.