Geomechanical modeling of induced seismicity source parameters and implications for seismic hazard assessment

Geophysics ◽  
2013 ◽  
Vol 78 (1) ◽  
pp. KS25-KS39 ◽  
Author(s):  
Bettina P. Goertz-Allmann ◽  
Stefan Wiemer
Keyword(s):  
Seismic Hazard ◽  
Pore Pressure ◽  
Stress Drop ◽  
Induced Seismicity ◽  
Critical Stress ◽  
Source Parameters ◽  
Differential Stress ◽  
Geomechanical Properties ◽  
Stress Changes ◽  
Stress States

We simulate induced seismicity within a geothermal reservoir using pressure-driven stress changes and seismicity triggering based on Coulomb friction. The result is a forward-modeled seismicity cloud with origin time, stress drop, and magnitude assigned to each individual event. Our model includes a realistic representation of repeating event clusters, and is able to explain in principle the observation of reduced stress drop and increased [Formula: see text]-values near the injection point where pore-pressure perturbations are highest. The higher the pore-pressure perturbation, the less critical stress states still trigger an event, and hence the lower the differential stress is before triggering an event. Less-critical stress states result in lower stress drops and higher [Formula: see text]-values, if both are linked to differential stress. We are therefore able to establish a link between the seismological observables and the geomechanical properties of the source region and thus a reservoir. Understanding the geomechanical properties is essential for estimating the probability of exceeding a certain magnitude value in the induced seismicity and hence the associated seismic hazard of the operation. By calibrating our model to the observed seismicity data, we can estimate the probability of exceeding a certain magnitude event in space and time and study the effect of injection depth and crustal strength on the induced seismicity.

scholarly journals Pore-pressure diffusion, enhanced by poroelastic stresses, controls induced seismicity in Oklahoma

2019 ◽  
Vol 116 (33) ◽  
pp. 16228-16233 ◽  
Author(s):  
Guang Zhai ◽  
Manoochehr Shirzaei ◽  
Michael Manga ◽  
Xiaowei Chen
Keyword(s):  
Pore Pressure ◽  
Induced Seismicity ◽  
Energy Demand ◽  
Regional Scale ◽  
Exceedance Probability ◽  
Resource Exploitation ◽  
Induced Earthquakes ◽  
Seismicity Rate ◽  
Pressure Diffusion ◽  
Stress Changes

Induced seismicity linked to geothermal resource exploitation, hydraulic fracturing, and wastewater disposal is evolving into a global issue because of the increasing energy demand. Moderate to large induced earthquakes, causing widespread hazards, are often related to fluid injection into deep permeable formations that are hydraulically connected to the underlying crystalline basement. Using injection data combined with a physics-based linear poroelastic model and rate-and-state friction law, we compute the changes in crustal stress and seismicity rate in Oklahoma. This model can be used to assess earthquake potential on specific fault segments. The regional magnitude–time distribution of the observed magnitude (M) 3+ earthquakes during 2008–2017 is reproducible and is the same for the 2 optimal, conjugate fault orientations suggested for Oklahoma. At the regional scale, the timing of predicted seismicity rate, as opposed to its pattern and amplitude, is insensitive to hydrogeological and nucleation parameters in Oklahoma. Poroelastic stress changes alone have a small effect on the seismic hazard. However, their addition to pore-pressure changes can increase the seismicity rate by 6-fold and 2-fold for central and western Oklahoma, respectively. The injection-rate reduction in 2016 mitigates the exceedance probability of M5.0 by 22% in western Oklahoma, while that of central Oklahoma remains unchanged. A hypothetical injection shut-in in April 2017 causes the earthquake probability to approach its background level by ∼2025. We conclude that stress perturbation on prestressed faults due to pore-pressure diffusion, enhanced by poroelastic effects, is the primary driver of the induced earthquakes in Oklahoma.

scholarly journals An approach to assessment of post mining-induced seismic hazard in Kolar Gold Fields mines – a review

2021 ◽  
Vol 69 (3) ◽  
pp. 88
Author(s):  
Praveena Das Jennifer ◽  
P. Porchelvan
Keyword(s):  
Seismic Hazard ◽  
Induced Seismicity ◽  
Seismic Vulnerability ◽  
Source Parameters ◽  
Seismic Source ◽  
Mining Area ◽  
Mining Induced Seismicity ◽  
Ground Collapse ◽  
Term Monitoring

A common challenge faced in underground hardrock mines worldwide is post mining-induced seismicity, as the events have been quite disastrous, causing risk to the structures and lives. In the recent years, many of the worked out mining areas are slowly getting populated and in due course of time shall be posing environmental threat to the people residing above and to the surface structures like sudden void formations or sudden ground collapse becoming visible on the surface. Worked out or closed mines have most of the time shown existence of post mining-induced seismicity signatures. Some of the closed mines showing post mining induced seismicity in Korea, South Africa, Sweden and India are being discussed. Post mining induced seismicity observed in Kolar Gold Fields worked out mine still being felt since closure of deeper levels is discussed. As mining depth increases especially in hard rock mines, magnitude of stress increases, hence, the occurrence and severity of postmining induced seismicity also increases. The problem becomes more serious if proper fund allocation is not done to investigate these areas, may be due to the absence of economic interest once the mine site has been abandoned and in many cases, direct investigations inside the mines may not be possible due to stability problems or due to the ingress of water into the void spaces of the mining area. Several approaches and techniques adopted by researcher’s world over are being discussed in this paper, with a view to gaining insight into the techniques of evaluation of seismic hazard. Seismic vulnerability assessment should integrate the effects of all the seismic events occurring at different locations of mining area during mining and post mining, along with their uncertainties also being considered. Based on the recorded data and some of the derived parameters from previous years, an attempt should be made to evaluate the existing risk prone areas. The past records of induced seismicity due to mining should be used as a precursor for identification of impending future events and their expected probable locations of occurrence. The methods discussed here for assessment of seismic hazard are based on direct waveform and seismic source parameters, parameters from indirect waveform methods, frequency-magnitude relationship based, and frequency content analysis based. From the assessment it is found that the choice of method that can be used depends on the period of monitoring (short-term monitoring, intermediate-term or long-term monitoring) and the objective of the study required to be achieved, this varies on site-to-site basis. The main focus is to show the importance and need to install a micro seismic monitoring system for long term assessment of seismic risk especially in abandoned/worked out mines showing post mining-induced seismicity.

New insights into the mechanisms of seismicity in the Azle area, North Texas

Geophysics ◽  
2019 ◽  
Vol 85 (1) ◽  
pp. EN1-EN15
Author(s):  
Rongqiang Chen ◽  
Xu Xue ◽  
Jaeyoung Park ◽  
Akhil Datta-Gupta ◽  
Michael J. King
Keyword(s):  
Fluid Flow ◽  
Stress Distribution ◽  
Pore Pressure ◽  
Induced Seismicity ◽  
Crystalline Basement ◽  
Water Volume ◽  
Optimization Approach ◽  
North Texas ◽  
Stress Changes ◽  
Area North

We have performed a site-specific study of the mechanics of induced seismicity in the Azle area, North Texas, using a coupled 3D fluid flow and poroelastic simulation model, extending from the overburden into the crystalline basement. The distinguishing feature of our study is that we account for the combined impact of water disposal injection and gas and water production on the pore pressure and stress distribution in this area. The model is calibrated using observed injection wellhead pressures and the location, timing, and magnitude of seismic events. We used a stochastic multiobjective optimization approach to obtain estimated ranges of fluid flow and poroelastic parameters, calibrated to the pressure, rate, and seismic event data. Mechanisms for induced seismicity were examined using these calibrated models. The calibrated models indicate no fluid movement or pressure increase in the crystalline basement, although there is plastic strain accumulation for the weaker elements along the fault in the basement. The accumulation of strain change appears to be caused by the unbalanced loading on different sides of the fault due to the differential in fluid injection and production. Previous studies ignored the produced gas volume, which is almost an order of magnitude larger than the produced water volume under reservoir conditions and which significantly impacts the pore pressure in the sedimentary formations and the stress distribution in the basement. A quantitative analysis indicates that the poroelastic stress changes dominate in the basement with no noticeable change in pore pressure. Even though the low-permeability faults in the basement are not in pressure communication with the Ellenburger formation, the poroelastic stresses transmitted to the basement can trigger seismicity without elevated pore pressure.

scholarly journals Prior oil and gas production can limit the occurrence of injection-induced seismicity: A case study in the Delaware Basin of western Texas and southeastern New Mexico, USA

Geology ◽  
2021 ◽  
Author(s):  
Noam Z. Dvory ◽  
Mark D. Zoback
Keyword(s):  
New Mexico ◽  
Pore Pressure ◽  
Induced Seismicity ◽  
Large Scale ◽  
Oil And Gas ◽  
Water Injection ◽  
Gas Production ◽  
Oil And Gas Production ◽  
Delaware Basin ◽  
Stress Changes

We demonstrate that pore pressure and stress changes resulting from several decades of oil and gas production significantly affect the likelihood of injection-related induced seismicity. We illustrate this process in the Delaware Basin (western Texas and southeastern New Mexico, USA), in which hydraulic fracturing and waste-water injection have been inducing numerous earthquakes in the southernmost part of the basin where there has been no prior oil and gas production from the formations in which the earthquakes are now occurring. In the seismically quiescent part of the basin, we show that pore-pressure and poroelastic-stress changes associated with prior oil and gas production make induced seismicity less likely. The findings of this study have important implications for the feasibility of large-scale carbon storage in depleted oil and gas reservoirs.

Relating spatial-temporal b-value patterns of induced earthquakes of the Groningen gas field to differential stress changes due to reservoir extraction

2021 ◽  
Author(s):  
Nilgün Güdük ◽  
Annemarie Muntendam-Bos ◽  
Jan Dirk Jansen
Keyword(s):  
Pore Pressure ◽  
B Value ◽  
Enhanced Geothermal Systems ◽  
Differential Stress ◽  
Gas Field ◽  
Seismic Slip ◽  
Stress Changes ◽  
Pressure Depletion ◽  
Groningen Gas Field ◽  
Event Magnitude

<p>The Gutenberg-Richter law describes the frequency-magnitude distribution of seismic events where its slope, the 'b-value', is commonly used to describe the relative occurrence of large and small events. Statistically significant b-value variations have been measured in laboratory experiments, mines, and various tectonic regimes (Wiemer & Wyss, 2002). An inversely proportional dependency of the b-value on the differential stress has been observed across different scales (Amitrano, 2003; Schorlemmer et al., 2005). Layland-Bachmann et al. (2012) have shown that this could explain the observed pattern of induced seismicity spatial-temporal b-value variations in Enhanced Geothermal Systems. In our study, we look for a similar relation applied to the Groningen gas field in the Netherlands.</p><p>It is well known that the poroelastic changes in differential stress during gas extraction are influenced by the offset of the reservoir layer across the fault. Recently, Jansen et al. (2019) and Lehner (2019) proposed an analytical solution for stress changes on offset faults due to reservoir depletion. In a parallel study, we extended this solution to include the development of aseismic slip under slip weakening and the derivation of the onset of seismic slip.<br>We utilize this formulation to derive the onset of seismic slip on theoretical faults of variable fault offset, dip, and reservoir thickness. Subsequently, we map our theoretical faults onto the pre-existing faults in the Groningen gas field, deriving fault segment-specific depletion levels at which the segment would become seismically active. We then simulate reservoir depletion conditions over time and assign an event magnitude to fault segments that move past their seismic activation depletion. To assign a magnitude, we use the observation that b-values are inversely proportional to differential stress, which is governed by the pore pressure depletion. Hence, we assume a simple inverse linear relation with pore pressure depletion. Each event magnitude is then randomly drawn from the probability density function of the Gutenberg-Richter distribution with the b-value assigned.<br>We aim to compare the obtained catalogue and its b-value distribution both in time and space to the observed event-size distribution of the Groningen gas field as derived by Muntendam-Bos and Güdük (EGU abstract 2021).</p>

Vp ∕ Vs ratio versus differential stress and rock consolidation — A comparison between rock models and time-lapse AVO data

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. C81-C94 ◽  
Author(s):  
Kenneth Duffaut ◽  
Martin Landrø
Keyword(s):  
Pore Pressure ◽  
Wave Velocity ◽  
Velocity Ratio ◽  
Time Lapse ◽  
P Wave ◽  
Pressure Increase ◽  
Prediction Methods ◽  
Differential Stress ◽  
Stress Changes ◽  
Key Parameter

The compressional to shear wave velocity ratio [Formula: see text] is an important parameter in seismic amplitude versus offset (AVO) analysis, and this parameter plays a key role especially for lithology and fluid prediction methods. The P-wave velocity is a key parameter in traditional pressure prediction methods, because overpressure often results in a velocity reduction. However, for AVO-based pore pressure prediction methods, one expects that the [Formula: see text] ratio also is a key parameter. The Hertz-Mindlin geomechanical model predicts a constant [Formula: see text] ratio as the differential stress changes in a dry package of identical spheres. Ultrasonic core measurements show increased [Formula: see text] ratios as the differential stress decreases, especially for unconsolidated wet sands. Thus, one is likely to assume that the [Formula: see text] ratio is dependent on rock consolidation. By combining the Hertz-Mindlin model with the Gassmann model, we show how to obtain a sim-ple rock-physics framework including both the differential stress and the degree of rock consolidation. We use the number of grain-to-grain contacts (coordination number) to represent the rock consolidation. For two field examples, we calibrate this consolidation parameter to in-situ stress conditions, then compare the predicted [Formula: see text] ratios for the overpressured reservoir conditions with observed time-lapse AVO changes. The correspondence between modeled and AVO-estimated [Formula: see text] ratios is good within the assumed accuracy of the real time-lapse AVO changes. In both cases, we observe an increase in the [Formula: see text] ratio as the differential stress decreases. In the first case, a pore pressure increase of [Formula: see text] is measured, whereas the other case shows a pressure increase of approximately [Formula: see text]. The first reservoir represents a low-to-medium-consolidated sandstone reservoir of 33% porosity on average, whereas the second reservoir is a more consolidated sand with similar porosities (30%).

Mining-Induced Tremors Source Modelling Applying InSAR

2021 ◽  
Author(s):  
Wojciech Witkowski ◽  
Magdalena Łukosz ◽  
Artur Guzy ◽  
Ryszard Hejmanowski
Keyword(s):  
Land Subsidence ◽  
Land Surface ◽  
Induced Seismicity ◽  
Negative Impact ◽  
Source Parameters ◽  
Mining Operations ◽  
Stress Changes ◽  
Post Shock ◽  
Surface Vibrations ◽  
Seismic Deformation

<p>Mining exploitation is associated with the occurrence of adverse environmental effects. The most serious of such effects is land subsidence. Although land subsidence can be well predicted and mitigated by several methods, nevertheless, the extraction of mineral deposits is also associated with induced seismicity. The occurrence of seismic events causes ground surface vibrations, land surface displacements and, in many cases, has a negative impact on the safety of surface infrastructure and the inhabitants of endangered areas. Despite this, the issue of induced seismicity is much less recognized and often ignored in the assessment of the negative impacts of mining exploitation.</p><p>Induced seismicity is related to stress changes in the reservoir and surrounding rock mass that may be caused by a variety of mechanisms. Consequently, the patterns of induced seismicity vary greatly over time and space for different fields or events within the same field. It is often difficult to determine the correlation between seismicity and mining precisely because of the lack of data detailing the pattern of exploitation at the various wells. As a result, the source mechanism of mining-induced tremor remains a subject of active research.</p><p>The research aimed to better identify the phenomenon of induced seismicity caused by mining operations. Research has been conducted in the area of underground copper ore mining in Poland. Firstly, we investigate the pre-and post-seismic land-surface movements following 8 mining-induced Mw 3.6-4.8 earthquakes that occurred between 2016 and 2018. We use Sentinel 1 data to derive these movements 2 weeks before and 4 weeks after the mainshock. The results of these studies show that no substantial pre-seismic surface movements are indicating the possibility of a seismic event occurring. However, the co-seismic deformation fields are quite symmetrical, the maximum land subsidence is almost 10 cm and occurs within a few days after the mainshock. In addition, the time series of post-seismic deformation shows a gradual decay and a good correspondence with the post-shock distribution.</p><p>Secondly, we use the Mogi model, assuming the elastic half-space, to invert co-seismic deformation fields and to obtain the source parameters of the mine-induced earthquakes. The spatial distribution of the epicenters indicates a correlation with the fields of mining exploitation. The results also show that the average depth of the hypocenter tremor is approx. 650 m. This corresponds to the depth of the stiff sandstone layers adjacent to the exploration. These layers accumulate the stress of post-exploitation voids. In addition, the modeling results indicate an approx. the volume of the displaced rock layers of 1.2 x 105 m3. This value shows a high correlation with the volume of post-shock troughs determined based on InSAR data.</p><p>The results of this study contribute to research into activities related to mining operations resulting in an induced-earthquake occurrence. This demonstrates InSAR's potential for quasi-constant monitoring of large-scale areas against seismic hazards caused by ongoing mining operations.</p>

scholarly journals Stress Drop, Seismogenic Index and Fault Cohesion of Fluid-Induced Earthquakes

2021 ◽  
Author(s):  
Serge A. Shapiro ◽  
Carsten Dinske
Keyword(s):  
Stress Drop ◽  
Induced Seismicity ◽  
Quantitative Characteristic ◽  
High Stress ◽  
Operation Time ◽  
Average Stress ◽  
Induced Earthquakes ◽  
Effective Stresses ◽  
Seismicity Rates

AbstractSometimes, a rather high stress drop characterizes earthquakes induced by underground fluid injections or productions. In addition, long-term fluid operations in the underground can influence a seismogenic reaction of the rock per unit volume of the fluid involved. The seismogenic index is a quantitative characteristic of such a reaction. We derive a relationship between the seismogenic index and stress drop. This relationship shows that the seismogenic index increases with the average stress drop of induced seismicity. Further, we formulate a simple and rather general phenomenological model of stress drop of induced earthquakes. This model shows that both a decrease of fault cohesion during the earthquake rupture process and an enhanced level of effective stresses could lead to high stress drop. Using these two formulations, we propose the following mechanism of increasing induced seismicity rates observed, e.g., by long-term gas production at Groningen. Pore pressure depletion can lead to a systematic increase of the average stress drop (and thus, of magnitudes) due to gradually destabilizing cohesive faults and due to a general increase of effective stresses. Consequently, elevated average stress drop increases seismogenic index. This can lead to seismic risk increasing with the operation time of an underground reservoir.

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