Abstract

In Germany geothermal energy production plays an important role in the area of renewable energies. The Upper Jurassic (Malm) aquifer beneath the Molasse Basin is predestinated for hydro-geothermal energy. As part of the research program PrognosPermae several laboratory tests were performed on Malm limestones and dolomites. The rock samples were characterized by uniaxial compressive strength (UCS), tensile strength, Young's Modulus, Poisson's ratio, bulk density, porosity and ultrasonic p- and s-wave velocities. Additionally water-permeability was measured in a triaxial cell under varying stress conditions. Ultrasonic wave velocities were investigated on dry and saturated samples, free to leak. The aim of this study is to ascertain a correlation between the lithology of the target horizon, permeability and the ultrasonic wave velocities. Furthermore, the influence of different stress levels on water-permeability of the specimens is investigated.

1. Introduction

Planning the exploitation of hydro-geothermal systems requires geophysical parameters from seismic and borehole measurements as well as the quantification of rock (hydro-) geomechanical properties in the laboratory. Many studies have already been performed on carbonate rocks (e.g. [1–6]). Nevertheless since geomechanical properties of carbonates depend strongly on depositional, diagenetic and tectonical processes it is essential to investigate these properties for the present conditions.

One of the main hydro-geothermal energy targets is located in the South German Molasse Basin. The aim of the presented research project is to develop a workflow to improve the potentiality diagnosis of the Upper Jurassic (Malm) aquifer. Therefore (hydro-) geomechanical parameters of carbonate samples were examined.

For the study borehole and seismic data of the investigation area close to Kirchweidach are available. Three wells, one of them a side-track, were drilled until a target depth of around 3,800 m (TVD). The characteristics of the Malm reservoir in a depth of 3,500 to 3,800 m is qualified by cuttings, thin sections and geological maps. For laboratory tests analog outcrop material with similar properties was chosen. To cover the range of possible rock formations detected in the cuttings limestone and dolomite of the Franconian Alp were selected. This work presents the first results of the experimental laboratory program.

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