An integrated study of geological and geophysical analysis to better characterize the mechanical behavior of a geothermal reservoir during hydraulic stimulation

David Sahara1, Thomas Kohl
1 Karsruhe Institute of Technology

O 5.3 in Deep geothermal reservoirs - synergies and conflicts

16.04.2016, 10:15-10:30, Audimax B, Geb. 30.95


The Enhanced Geothermal System (EGS) program of Soultz-sous-Forêts is circulated around three wells (GPK2, GPK3 and GPK4) drilled to a depth of about 5000 m. Hydraulic stimulations were performed in order to increase the permeability of the reservoir of the reservoir and the connectivity among the wells. The stimulation of GPK4 was carried out in two stages, in September 2004 and in February 2005, followed by an acidification test performed in March 2005. In this work we characterize the reservoir section based on integrated geological and geophysical information, i.e. breakout heterogeneity, clay content, cutting analysis, slip tendency. Two zones which have different lithology, fracture and breakout density are presented. The microseismic events distribution also support this zonation. Though the flow log test shows comparable amount of water entering both zones, 85% of the events are occurred in the lower part of the reservoir. The microseismic distribution infer that the fracture network in the lower part are more critically stressed, hence, it is easier to reactivate those fractures. This hypothesis is supported by the slip tendency analysis which shows that the lower reservoir has higher value of slip tendency for both small and major fractures. Furthermore, the density of the fractures are higher in the lower part of the reservoir. The microseismic events are concentrated in one fault intersected the well at depth of around 4750 m TVD. The high clay content observes in this fault core give us a hint that the major energy is released through creeping mechanism, hence only relatively low number of events are observed during this simulation, compare to the other wells simulation. All of the results presented in this study show us that the analysis of integrated geophysical and geological data collected from log data could provide us some essential information about the reservoir characteristic. This information could be very useful for the reservoir engineering in order to better investigate the risk and the success ratio of a hydraulic stimulation beforehand.      

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