Powered by Indico 

Stimulation of reservoir and induced microseismicity - Zurich, Switzerland, Workshop3
Stimulation of reservoir and induced microseismicity - Zurich, Switzerland, Workshop3
from 29 June 2006 to 01 July 2006 Kartause Ittingen, Switzerland
Characterization of reservoir using microseismicity induced during stimulation tests: contribution from tomographic analysis and faulting mechanisms
Tomographic and faulting studies represent two efficient ways to characterize the 
behaviour of geothermal reservoirs during stimulation tests. Tomographic analysis of 
induced microseismicity give two types of results: the 3D distribution of seismic 
velocities within the medium and precise relocation of the microseismic events, 
using the velocity model previously found. Analysis of faulting mechanisms, 
especially through focal mechanisms studies, is able to give informations on the 
main shearing structure and the type of movements that they support. 
In the case of the stimulation of EGS-type reservoir, numerous microseismic events 
are generally recorded; that allows performing reliable tomographic calculation. 
Moreover, this huge quantity of data can be used to follow the temporal evolution of 
the 3D distribution of the seismic velocities, which brings useful information on 
the effect of the circulating water on the physical properties of the reservoir. 
Using a velocity model that takes into account the temporal variation of the seismic 
velocities allows getting a very precise relocation of the microseismic events. 
This, combined with the analysis of the faulting mechanisms through the reservoir 
gives a rather good view of the shearing processes in the reservoir.

In this study, we analyses the microseismic events induced during two tests: the 
stimulation of GPK2 in 2000 and of GPK3 in 2003, both performed between 4.5 and 5 km 
depth. The temporal evolution of the 3D distribution of seismic velocities during 
the injections is calculated in both cases, leading to conclusions about the 
variations of the properties of the reservoir. The analysis of the relocated 
microseismic cloud demonstrates that some major structures, probably corresponding 
to major faults, play a dominant role in the generation of seismic events, both of 
small and higher magnitude.

From the focal mechanisms study, it appears that normal faulting, with a more or 
less pronounced strike-slip component, represent the major regime, but quasi pure 
strike-slip movements are also observed. From the recorded first-motion polarity 
data, an estimate of the stress tensor has been calculated and then applied to the 
nodal planes determined from focal mechanisms: orientation and dip of fractures 
having sheared can thus be retrieved. Moreover, all determined focal mechanisms show 
a double-couple solution, but from the analysis of the seismic moment tensor for 
several 2003 events, we have been able to quantify the proportion of the non-double-
couple (NDC) component, which correspond to the proportion of opening in the 
shearing process. It is interesting to observe that events in the vicinity of the 
injection well GPK3 show a higher NDC component, than those far from the injection.

The combination of results given by all these methods, applied to two different 
datasets gives thus very valuable information on the mechanical processes that occur 
within the reservoir under stimulation conditions.
Id: 16
Place: Kartause Ittingen, Switzerland
CH-8532 Warth TG
Starting date:
30-Jun-2006   11:35
Duration: 15'
Primary Authors: CUENOT, Nicolas (GEIE Exploitation Minière de la Chaleur)
Co-Authors: CHARLéTY, Jean (IPGS-EOST Strasbourg)
DORBATH, Catherine (IPGS-EOST Strasbourg)
DORBATH, Louis (IPGS-EOST Strasbourg)
HAESSLER, Henri (IPGS-EOST Strasbourg)
Presenters: CUENOT, Nicolas
Material: paper Paper
slides Slides

ENGINE | Powered by CERN Indico 0.94 | | Last modified 25 April 2008 16:33 | HELP