Fracture networks are used for underground heat exchangers, i.e. reservoirs, in the
Enhanced Geothermal 
Systems (EGS).  Each fracture composed of the network is spread over a relatively
large area of several 
hundreds square meters, but its aperture is limited to several millimeters at
maximum.  There is no way to 
detect directly such a thin structure nor the fluid flow in it from ground surface
through a huge rock mass 
with few thousands meters in thickness, while those factors are important for
construction of the EGS.  On the 
other hand, a number of microseismic events are observed during hydraulic
stimulation.  It is believed that the 
occurrence of those events is associated with the fluid flow through fracture
networks caused by the 
stimulation.  Therefore it may be possible to estimate the fluid flow from the
observed micoseismic events.  
To this end, we have considered the sequence in which hydraulic stimulation leads to
the occurrence of 
microseismic events.  Then, based on those consideration, we have come up with an
idea to integrate the data 
of microseismic events for estimating pore pressure propagation along the fracture
network associated with 
hydraulic stimulation.  Furthermore, we have shown that the location of flow pathways
and the hydraulic 
conductivity along them could be estimated from the pore pressure distribution
estimated from microseismic 
events.  To do this, we assume an appropriate model of flow pathway structure and
adjust it as the pore 
pressure distribution computed by the model agrees well with that estimated from
micro-seismic events.  We 
have applied these methods to the Soultz and Cooper Basin HDR fields.  As a result,
we have succeeded to 
reach plausible estimations of pressure propagation during hydraulic stimulation and
flow pathway structures 
for each field.

CH-8532 Warth TG
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