Characterisation of a geothermal reservoir using microseismic data

In this work we considered the geological structure at the German deep drill site (KTB) as a prototype of a geothermal system. We used microseismic data in combination with surface seismic imaging results for characterization of the geothermal reservoir. First, we located microseismicity induced by fluid injection experiment. Then, we applied SBRC approach and estimated rock diffusivity using three clouds of microseismicity which corresponded to two different fault zones and background rock. Using the large scale surface reflection imaging result and assuming positive correlation between the seismic reflectivity and the hydraulic permeability, we constructed 3D permeability model. Finally, we applied our reflection microseismic imaging approach to the microseismic waveforms recorded at single three-component geophone and constructed the high-resolution image of inner structure of the fault zone. KTB project The German Deep Drilling Site (KTB) is located on basement rock at the western margin of the Bohemian Massif. About 4 km west of the KTB, the Franconian Lineament outcrops, a NW-SE trending, deep-reaching system of thrust faults, which separates the basement block from Permo-Mesozoic sediments. During a one-year hydraulic experiment in 2004/2005, water was constantly injected in the open-bottom section of the KTB pilot hole at 4 km depth, where the borehole intersects one of these faults. This fault (SE2 reflector) is characterised by steeply dipping seismic reflections (Harjes et al. (1997)). The seismicity was monitored by a seismic network, which consisted of a borehole seismometer in KTB main hole at 200 m horizontal distance from the injection source and variable number of near-surface stations (on average 10–15 stations). Most of the stations were installed within radius of 3 km from the KTB. All instruments were 3-component seismometers and data were recorded continuously at sample rates 200–1000 Hz. 10 km Figure 2. Left: Configuration of the KTB injection test in 4 km depth (green bullet) and the seismic sensor