Title:

Improving Hydraulic Stimulation Efficiency by Means of Real-Time Monitoring

Authors:

S. Baisch, R. Weidler, R. Voeroes H. Tenzer , D. Teza

Key Words:

hydraulic stimulation, real-time monitoring, hydraulic stimulation efficiency

Geo Location:

KTB Oberpfalz, Germany; Bad Urach, Germany; Soultz-sous-Forets, France

Conference:

Stanford Geothermal Workshop

Year:

2004

Session:

HOT DRY ROCK

Language:

English

File Size:

961KB

View File:

Abstract:

In contrast to geo-pressurized hydrothermal systems,
where it is often possible to exploit the heat in a
simple production mode, EGS (Enhanced
Geothermal Systems) or HDR (Hot Dry Rock)
systems in low permeability host rocks require the re-injection
of fluid in order to sustain the pressure and
a steady flow in the reservoir. In the ideal case, this is
realized in a virtually closed loop system with a mass
balanced circulation between the production and the
injection wells. In turn, a balanced circulation places
high demands on the connectivity of the man-made
subsurface heat exchangers. To achieve the desired
connections, a hydraulic stimulation has to be
designed and performed in the context of the total
reservoir geometry and not only for each well
separately.
Numerical computations show that even small gaps
between the stimulated zones result in a significant
drop in productivity, even though each well has been
individually stimulated to a high degree. For
example, such a situation can arise when a
stimulation job is aborted too early. On the other
hand, field examples also show cases where the
efficiency of a hydraulic stimulation decreased
during pumping without being notified in the
hydraulic data. This creates superfluous costs if the
pumping strategy is not adjusted accordingly.
The risk of both, creating heat exchangers of poor
connectivity and inefficient pumping can be
significantly reduced when the spatio-temporal
expansion of the stimulated zones is monitored and
interpreted already during the operation. For this
purpose, the analysis of microseismic events
occurring during a massive hydraulic stimulation has
established itself as the most promising method.
However, the lack of computing power and reliable
and fast algorithms, as well as the extraordinary size
of the data sets, sometimes exceeding several ten-thousand
events, has limited a real-time analysis of
microseismic data in past experiments. In the field,
mainly, and information on the spatial impact of the
operation was often not available when needed.
Recent developments have yielded a software
package capable to process and interpret huge
microseismic data sets automatically and in real-time
speed. By an integrated seismo-hydraulic analysis
this software provides a valuable tool for the decision
making in the field.


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