Paths Forward to Understanding and Managing Induced Seismicity in Energy Technology Development - Induced Seismicity Potential in Energy Technologies - page 122

Two spatial aspects of risk analysis are important to consider in the context of induced
seismicity:
1. Multiple structures that can be damaged . A single well that induces earthquakes
large enough to cause damage at the surface may damage multiple structures at
the surface. If seismicity migrates during well operations (which is common for
disposal wells), earthquakes have multiple opportunities to impact many struc-
tures. Even a small community located near a single well will have multiple
structures with a range of vulnerabilities to ground shaking. Multiple structures
give an increased chance of having one or a few structures with very weak re-
sistance to ground shaking. Operations located in areas with many structures,
such as the Basel, Switzerland, geothermal project, clearly have higher risk than
a similar project in an unpopulated area. Likewise, CCS operations that are
located at power plants in or near urban areas and which have the potential
through injections of large amounts of CO 2 over long time periods to increase
reservoir pressures over large areas that may have surface developments may have
increased risk.
2. Multiple well locations . The risk associated with induced seismicity has to be
evaluated in terms of the sources of human activities. A geothermal operation, for
example, may have multiple injection wells, each of which may generate seismic
events that can affect different communities. For a large petroleum field, multiple
wells may be used to inject fluid for secondary recovery, and each well may gener-
ate earthquakes that can affect separate communities. The spatial distribution for
an entire industry project (e.g., underground injection of CO 2 ) may be very large,
and a risk analysis of the entire project would necessarily include that large spatial
distribution and the multiple structures in that spatial area which induced seismic
events might affect.
If a small number of wells (e.g., 10) are put in operation, the maximum shaking asso-
ciated with earthquakes induced by those 10 wells can be described (Figure 5.4). In this
example, a majority of wells (9 out of 10) will produce only felt motion, and only 1 out of 10
will produce ground motion with the potential for minor damage. No observations of
moderate or greater (abbreviated hereafter as “moderate+”) damage occur in this example.
If many wells (e.g., 1,000) are put into operation, a histogram of the maximum shaking
induced by those 1,000 wells would show that 250 wells are expected to produce ground
motions capable of minor damage to structures. Ten wells are expected to produce
ground motions capable of moderate+ damage to structures.