Results of the Geothermal Energy Project Hamburg - Allerrnoehe

Abstract

In the south-eastern area of the city of Hamburg, in depths of about 3000 m the Mittelrhaet- Hauptsandstein exists. In order to assess the geothermal potential of this aquifer, in 1997, an abandoned oil production well was deepened from 2178 down to 3305 m. From 3197 to 3290 my 4 sandstone horizons of 12,8,25, and 28 m thickness were found. The grain size distribution of the sandstone is promising, but the originally large pore volume is mostly cemented with anhydrite. Pumping and injection tests, laboratory examinations, and predictions based on a NMR log yielded comparable permeability values of about 10 mD. Thus, the well yield is too low to allow an economical use, despite a considerable high temperature of 128?C. So far, it is unknown, whether the anhydrite cementation is limited to small areas and where it occurs. These questions are crucial for any further hydrothermal energy use in this region. In areas without cementation, a high geothermal potential can be expected, as all other parameters of the sandstone have proved to be promising. The state geological survey (Geologisches Landesamt (GLA) Hamburg) has started to examine the drill cores on geological parameters determining the anhydrite cementation. Xray radioscopy showed merent cementation patterns, which seem to contain important diagenetic information. In addition, strontium and other trace elements analysis with electron and proton microprobe analysis, secondary ion mass spectrometry (SIMS), and laser microprobe for material analysis (LAMMA), examinations with global time markers, microthermometrical as well as mineralogical and sedimentological investigations have started or are planned. In situ investigations in the borehole Allermoehe 1 are very necessary, but yet not possible, because of a broken liner. After borehole reconstruction, pumping and injection tests, seismic experiments as well as hydraulic and chemical stimulation tests could yield important contributions to understand the anhydrite cementation and to reduce the drilling risk in further hydrothermal exploration projects in Northern Germany.