| Title | Modelling of Pore Pressure Response Due to Hydraulic Stimulation Treatments at the Geothermal Research Doublet EGrSk03/90 and GtGrSk04/05 in Summer 2007 |
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| Authors | Guido Bloecher, Inga Moeck, Harald Milsch & Guenter Zimmermann |
| Year | 2008 |
| Conference | Stanford Geothermal Workshop |
| Keywords | hydraulic fracturing, hydro-mechanical reservoir modelling |
| Abstract | In order to complete the doublet system for geothermal power production, a second research well has been finished in January 2007 at the geothermal research drill site Gross-Schoenebeck (40 km north of Berlin/Germany). To enhance the productivity of the production well GtGrSk4/05 three hydraulic fracture treatments were performed at different reservoir sections. The reservoir is located in -3850 to -4258 m depth within the Lower Permian of the NE German Basin. The reservoir rock can be classified into two lithological units from base to top: volcanic rocks (andesitic rocks) and siliciclastics ranging from conglomerates to fine grained sandstones (fluvial sediments). The first treatment (water frac) took place in the volcanic rocks followed by two gel proppant treatments in the sandstones that are characterised by a permeability of 50-100 mD. During the stimulation the water table at the injection well EGrSk3/90 (500 m distance from production well) as well as the micro-seismic events were monitored. Two important facts were observed: An instantaneous pressure response due to the hydraulic stimulation treatments and a long-termed pressure increase depending on the injected water volume. The rapidly water level increase in the offsetting well EGrSk3/90 was unexpectedly high and led to a wide range of interpretations. To reveal the hydro-thermal-mechanical conditions during stimulation a 3D model was developed, which can reconstruct the stimulation treatments. This model includes a hydro-thermal-mechanical coupling, a discrete modeling of the fractured reservoir rocks and the implementation of the deviated well. We will present the development from a structural-geological model (developed with earthVision/DGI) to a 3D hydro-thermal-mechanical finite element model. (RockFlow/Geosys). Furthermore, we will show how the model can reduce the ambiguity of the observed field data. |