8 research outputs found
Scaling of seismicity induced by nonlinear fluid-rock interaction after an injection stop
Fluid injections into unconventional reservoirs, performed for fluid-mobility
enhancement, are accompanied by microseismic activity also after the
injection. Previous studies revealed that the triggering of seismic events can
be effectively described by nonlinear diffusion of pore fluid pressure
perturbations where the hydraulic diffusivity becomes pressure dependent. The
spatiotemporal distribution of postinjection-induced microseismicity has two
important features: the triggering front, corresponding to early and distant
events, and the back front, representing the time-dependent spatial envelope
of the growing seismic quiescence zone. Here for the first time, we describe
analytically the temporal behavior of these two fronts after the injection
stop in the case of nonlinear pore fluid pressure diffusion. We propose a
scaling law for the fronts and show that they are sensitive to the degree of
nonlinearity and to the Euclidean dimension of the dominant growth of
seismicity clouds. To validate the theoretical finding, we numerically model
nonlinear pore fluid pressure diffusion and generate synthetic catalogs of
seismicity. Additionally, we apply the new scaling relation to several case
studies of injection-induced seismicity. The derived scaling laws describe
well synthetic and real data
Autonomous decision-making against induced seismicity in deep fluid injections
The rise in the frequency of anthropogenic earthquakes due to deep fluid
injections is posing serious economic, societal, and legal challenges to
geo-energy and waste-disposal projects. We propose an actuarial approach to
mitigate this risk, first by defining an autonomous decision-making process
based on an adaptive traffic light system (ATLS) to stop risky injections, and
second by quantifying a "cost of public safety" based on the probability of an
injection-well being abandoned. The ATLS underlying statistical model is first
confirmed to be representative of injection-induced seismicity, with examples
taken from past reservoir stimulation experiments (mostly from Enhanced
Geothermal Systems, EGS). Then the decision strategy is formalized: Being
integrable, the model yields a closed-form ATLS solution that maps a risk-based
safety standard or norm to an earthquake magnitude not to exceed during
stimulation. Finally, the EGS levelized cost of electricity (LCOE) is
reformulated in terms of null expectation, with the cost of abandoned
injection-well implemented. We find that the price increase to mitigate the
increased seismic risk in populated areas can counterbalance the heat credit.
However this "public safety cost" disappears if buildings are based on
earthquake-resistant designs or if a more relaxed risk safety standard or norm
is chosen.Comment: 8 pages, 4 figures, conference (International Symposium on Energy
Geotechnics, 26-28 September 2018, Lausanne, Switzerland
Understanding Slow Deformation Before Dynamic Failure
Slow deformation and fracturing have
been shown to be leading mechanisms towards failure,
marking earthquake ruptures, flank eruption onsets
and landslide episodes. The common link among
these processes is that populations of microcracks
interact, grow and coalesce into major fractures. We
present (a) two examples of multidisciplinary field
monitoring of characteristic âlarge scaleâ signs of
impending deformation from different tectonic setting,
i.e. the Ruinon landslide (Italy) and Stromboli
volcano (Italy) (b) the kinematic features of slow
stress perturbations induced by fluid overpressures
and relative modelling; (c) experimental rock deformation
laboratory experiments and theoretical modelling
investigating slow deformation mechanisms,
such stress corrosion crack growth. We propose
an interdisciplinary unitary and integrated approach
aimed to:
(1) transfer of knowledge between specific fields,
which up to now aimed at solve a particular problem;
(2) quantify critical damage thresholds triggering
instability onset; (3) set up early warning models for
forecasting the time of rupture with application to volcanology,
seismology and landslide risk prevention.Published229-2472.3. TTC - Laboratori di chimica e fisica delle roccereserve