Here is the third part of our presentation of recent papers related to induced seismicity. If you want to advertise your paper or have any suggestions, do not hesitate to contact us.
Eisner, L., Gei, D., Hallo, M., Opršal, I., and Ali, M. (2013). ”The peak frequency of direct waves for microseismic events.” GEOPHYSICS, 78(6), A45–A49. doi: 10.1190/geo2013-0197.1.
Direct seismic waves (P- or S-waves) are used to locate and further characterize microseismic events. The resolution of information obtained from direct waves depends on the peak frequencies of the waveforms. The peak frequency results from combination of the source, propagation, and the receiver effects. For frequencies below the corner frequency, propagation effects control the peak frequency in observed seismograms of microseismic events. The frequency dependence of direct body waves can be modeled by attenuation, specifically the global attenuation factor. This model is consistent with observed data along surface profiles explaining the difference between the peak frequencies of P- and S-waves. In addition, the model is consistent with the peak frequencies observed on downhole monitoring arrays. This can be used to invert effective attenuation providing additional unique measurement from microseismic events. The corner frequency can be estimated from the average stress drop and analytical source models such as a circular crack model. Typical stress drops for various magnitude ranges are discussed. The peak frequencies are usually below the corner frequencies of microseismic events smaller than moment magnitude 0.7 for surface monitoring and moment magnitude −0.5 for downhole monitoring. Understanding of the frequency dependence of the direct waves allows us to optimally design monitoring networks and mainly invert effective attenuation providing unique measurement from microseismic monitoring.
Link: Article Website
Eisner, L., Hallò, M., Janskà, E., Opršal, I., Matoušek, P., Clarke, H., Turner, P., Harper, T., and Styles, P. (2013) Lessons learned from hydraulic stimulation of the Bowland Shale. SEG Technical Program Expanded Abstracts 2013: pp. 4516-4520. doi: 10.1190/segam2013-0239.1.
Shale gas development has caused an energy revolution in the USA over the past decade. However, the transfer of technology abroad has been generally slow and in case of Europe negligible. One of the aspects slowing down shale development is induced or triggered seismicity. This study summarizes main findings from the analysis of the passive seismic data available for hydraulic stimulation of Bowland Shale in Preese Hall well, UK, in 2011. We show that seismicity was most likely induced by hydraulic fracturing and that unusually large seismic events occurred already during the hydraulic fracturing. These events can be used to provide warning and modify hydraulic fracturing treatments in future to avoid induced seismicity which would be socially unacceptable.
Link: Article Website.
Shapiro, S. A., O. S. Krüger, and C. Dinske (2013), Probability of inducing given-magnitude earthquakes by perturbing finite volumes of rocks, J. Geophys. Res. Solid Earth, 118, 3557–3575, doi:10.1002/jgrb.50264.
Fluid-induced seismicity results from an activation of finite rock volumes. The finiteness of perturbed volumes influences frequency-magnitude statistics. Previously we observed that induced large-magnitude events at geothermal and hydrocarbon reservoirs are frequently underrepresented in comparison with the Gutenberg-Richter law. This is an indication that the events are more probable on rupture surfaces contained within the stimulated volume. Here we theoretically and numerically analyze this effect. We consider different possible scenarios of event triggering: rupture surfaces located completely within or intersecting only the stimulated volume. We approximate the stimulated volume by an ellipsoid or cuboid and derive the statistics of induced events from the statistics of random thin flat discs modeling rupture surfaces. We derive lower and upper bounds of the probability to induce a given-magnitude event. The bounds depend strongly on the minimum principal axis of the stimulated volume. We compare the bounds with data on seismicity induced by fluid injections in boreholes. Fitting the bounds to the frequency-magnitude distribution provides estimates of a largest expected induced magnitude and a characteristic stress drop, in addition to improved estimates of the Gutenberg-Richter a and b parameters. The observed frequency-magnitude curves seem to follow mainly the lower bound. However, in some case studies there are individual large-magnitude events clearly deviating from this statistic. We propose that such events can be interpreted as triggered ones, in contrast to the absolute majority of the induced events following the lower bound.
Link: Article website.
Masuda, K. (2013), Source duration of stress and water-pressure induced seismicity derived from experimental analysis of P wave pulse width in granite, Geophys. Res. Lett., 40, 3567–3571, doi:10.1002/grl.50691.
Pulse widths of P waves in granite, measured in the laboratory, were analyzed to investigate source durations of rupture processes for water-pressure induced and stress-induced microseismicity. Water was injected into a dry granite sample under constant axial stress of about 70% of fracture strength and a confining pressure of 40 MPa. After the effects of event size and hypocentral distance were removed from observed pulse widths, the ratio of the scaled source durations of water-pressure induced and stress-induced microseismicity was 0.52. The difference in the scaled source durations between water-pressure induced and stress-induced microseismicity suggests that water-pressure induced microseismicity involves a greater rupture velocity or a more equidimensional fault geometry than stress-induced microseismicity. These results suggest that pulse width analysis of P waveforms can be used to distinguish water-pressure induced events from those induced by regional stress and to characterize the faulting process.
Link: Article website.
Kim, W.-Y. (2013), Induced seismicity associated with fluid injection into a deep well in Youngstown, Ohio, J. Geophys. Res. Solid Earth, 118, 3506–3518, doi:10.1002/jgrb.50247.
Over 109 small earthquakes (Mw 0.4–3.9) were detected during January 2011 to February 2012 in the Youngstown, Ohio area, where there were no known earthquakes in the past. These shocks were close to a deep fluid injection well. The 14 month seismicity included six felt earthquakes and culminated with a Mw 3.9 shock on 31 December 2011. Among the 109 shocks, 12 events greater than Mw 1.8 were detected by regional network and accurately relocated, whereas 97 small earthquakes (0.4 < Mw < 1.8) were detected by the waveform correlation detector. Accurately located earthquakes were along a subsurface fault trending ENE-WSW—consistent with the focal mechanism of the main shock and occurred at depths 3.5–4.0 km in the Precambrian basement. We conclude that the recent earthquakes in Youngstown, Ohio were induced by the fluid injection at a deep injection well due to increased pore pressure along the preexisting subsurface faults located close to the wellbore. We found that the seismicity initiated at the eastern end of the subsurface fault—close to the injection point, and migrated toward the west—away from the wellbore, indicating that the expanding high fluid pressure front increased the pore pressure along its path and progressively triggered the earthquakes. We observe that several periods of quiescence of seismicity follow the minima in injection volumes and pressure, which may indicate that the earthquakes were directly caused by the pressure buildup and stopped when pressure dropped.
Link: Article website.