Parametric analysis of the elastohydrodynamic lubrication efficiency on induced seismicity

SUMMARY During reservoir stimulations, the injection of fluids with variable viscosities can trigger seismicity. Several fault lubrication mechanisms have been invoked to explain the dynamic stress drop occurring during those seismic events. Here, we perform a parametric analysis of the elastohydrodynamic fault lubrication mechanism to assess its efficiency during fluid-induced earthquakes. The efficiency of the mechanism is measured with the dimensionless Sommerfeld number S. Accordingly, we analysed eight well-documented cases of induced seismicity associated with the injection of fluids whose viscosities range from 1 mPa s (water) to 100 mPa s (proppant). We collected information related to the in situ stress field, fault orientation and geometry, moment of magnitude and static stress drop of the events. These parameters allow us to analyse the variation in the Sommerfeld number. Our results show that the estimated dynamic friction on the fault during the event is compatible with the fault weakening predicted by the elastohydrodynamic lubrication theory, particularly for highly viscous fluids.

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

Rock Mechanics and Rock Engineering ◽

10.1007/s00603-021-02420-3 ◽

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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Study of the in situ stress field in a deep valley and its influence on rock slope stability in Southwest China

Bulletin of Engineering Geology and the Environment ◽

10.1007/s10064-020-02094-1 ◽

2021 ◽

Author(s):

Yibing Ning ◽

Huiming Tang ◽

John V. Smith ◽

Bocheng Zhang ◽

Peiwu Shen ◽

...

Keyword(s):

Stress Field ◽

Slope Stability ◽

Rock Slope ◽

Southwest China ◽

In Situ Stress ◽

Rock Slope Stability ◽

In Situ Stress Field

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The effect of a deviatoric stress on physical rock properties. An experimental study simulating the in-situ stress field at the KTB drilling site, Germany

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts ◽

10.1016/0148-9062(95)93294-y ◽

1995 ◽

Vol 32 (5) ◽

pp. A222

Keyword(s):

Experimental Study ◽

Stress Field ◽

In Situ Stress ◽

Deviatoric Stress ◽

Rock Properties ◽

Drilling Site ◽

In Situ Stress Field ◽

Physical Rock Properties ◽

Physical Rock

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A Source Physics Interpretation of Nonself-Similar Double-Corner-Frequency Source Spectral Model JA19_2S

Seismological Research Letters ◽

10.1785/0220210098 ◽

2022 ◽

Author(s):

Chen Ji ◽

Ralph J. Archuleta

Keyword(s):

Stress Drop ◽

Wave Speed ◽

Dynamic Stress ◽

Corner Frequency ◽

Rupture Velocity ◽

Scaling Relation ◽

Shear Wave Speed ◽

Dynamic Stress Drop ◽

Static Stress Drop ◽

Frequency Source

Abstract We investigate the relation between the kinematic double-corner-frequency source spectral model JA19_2S (Ji and Archuleta, 2020) and static fault geometry scaling relations proposed by Leonard (2010). We find that the nonself-similar low-corner-frequency scaling relation of JA19_2S model can be explained using the fault length scaling relation of Leonard’s model combined with an average rupture velocity ∼70% of shear-wave speed for earthquakes 5.3 < M< 6.9. Earthquakes consistent with both models have magnitude-independent average static stress drop and average dynamic stress drop around 3 MPa. Their scaled energy e˜ is not a constant. The decrease of e˜ with magnitude can be fully explained by the magnitude dependence of the fault aspect ratio. The high-frequency source radiation is generally controlled by seismic moment, static stress drop, and dynamic stress drop but is further modulated by the fault aspect ratio and the relative location of the hypocenter. Based on these two models, the commonly quoted average rupture velocity of 70%–80% of shear-wave speed implies predominantly unilateral rupture.

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