scholarly journals Effective normal stress alteration due to pore pressure changes induced by dynamic slip propagation on a plane between dissimilar materials

2006 ◽  
Vol 111 (B10) ◽  
Author(s):  
John W. Rudnicki ◽  
James R. Rice
Keyword(s):  
Normal Stress ◽  
Pore Pressure ◽  
Dissimilar Materials ◽  
Effective Normal Stress ◽  
Pressure Changes ◽  
Dynamic Slip

Two types of reservoir-induced seismicity

1988 ◽  
Vol 78 (6) ◽  
pp. 2025-2040
Author(s):  
D.W. Simpson ◽  
W.S. Leith ◽  
C.H. Scholz
Keyword(s):  
Normal Stress ◽  
Pore Pressure ◽  
Induced Seismicity ◽  
Elastic Stress ◽  
Pore Space ◽  
Temporal Distribution ◽  
The Other ◽  
Elastic Response ◽  
Reservoir Induced Seismicity ◽  
Effective Normal Stress

Abstract The temporal distribution of induced seismicity following the filling of large reservoirs shows two types of response. At some reservoirs, seismicity begins almost immediately following the first filling of the reservoir. At others, pronounced increases in seismicity are not observed until a number of seasonal filling cycles have passed. These differences in response may correspond to two fundamental mechanisms by which a reservoir can modify the strength of the crust—one related to rapid increases in elastic stress due to the load of the reservoir and the other to the more gradual diffusion of water from the reservoir to hypocentral depths. Decreased strength can arise from changes in either elastic stress (decreased normal stress or increased shear stress) or from decreased effective normal stress due to increased pore pressure. Pore pressure at hypocentral depths can rise rapidly, from a coupled elastic response due to compaction of pore space, or more slowly, with the diffusion of water from the surface.

scholarly journals Precise Monitoring of Pore Pressure at Boreholes Around Nankai Trough Toward Early Detecting Crustal Deformation

2021 ◽  
Vol 9 ◽  
Author(s):  
Keisuke Ariyoshi ◽  
Toshinori Kimura ◽  
Yasumasa Miyazawa ◽  
Sergey Varlamov ◽  
Takeshi Iinuma ◽  
...  
Keyword(s):  
Normal Stress ◽  
Pore Pressure ◽  
Crustal Deformation ◽  
Nankai Trough ◽  
Time Lag ◽  
Pressure Change ◽  
Ocean Modeling ◽  
Effective Normal Stress ◽  
Seafloor Pressure ◽  
The Impact

In our recent study, we detected the pore pressure change due to the slow slip event (SSE) in March 2020 at the two borehole stations (C0002 and C0010), where the other borehole (C0006) close to the Nankai Trough seems not because of instrumental drift for the reference pressure on the seafloor to remove non-crustal deformation such as tidal and oceanic fluctuations. To overcome this problem, we use the seafloor pressure gauges of cabled network Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) stations nearby boreholes instead of the reference by introducing time lag between them. We confirm that the time lag is explained from superposition of theoretical tide modes. By applying this method to the pore pressure during the SSE, we find pore pressure change at C0006 about 0.6 hPa. We also investigate the impact of seafloor pressure due to ocean fluctuation on the basis of ocean modeling, which suggests that the decrease of effective normal stress from the onset to the termination of the SSE is explained by Kuroshio meander and may promote updip slip migration, and that the increase of effective normal stress for the short-term ocean fluctuation may terminate the SSE as observed in the Hikurangi subduction zone.

Dilation and compaction accompanying changes in slip velocity in clay-bearing fault gouges

2021 ◽  
Author(s):  
Isabel Ashman ◽  
Daniel Faulkner
Keyword(s):  
Normal Stress ◽  
Pore Pressure ◽  
Volume Change ◽  
Slip Velocity ◽  
Fault Slip ◽  
Slow Slip ◽  
Volume Changes ◽  
Effective Normal Stress ◽  
Earthquake Nucleation ◽  
Fault Gouges

<p>Many natural fault cores comprise volumes of extremely fine, low permeability, clay-bearing fault rocks. Should these fault rocks undergo transient volume changes in response to changes in fault slip velocity, the subsequent pore pressure transients would produce significant fault weakening or strengthening, strongly affecting earthquake nucleation and possibly leading to episodic slow slip events. Dilatancy at slow slip velocity has previously been measured in quartz-rich gouges but little is known about gouge containing clay. In this work, the mechanical behaviour of synthetic quartz-kaolinite fault gouges and their volume response to velocity step changes were investigated in a suite of triaxial deformation experiments at effective normal stresses of 60MPa, 25MPa and 10MPa. Kaolinite content was varied from 0 to 100wt% and slip velocity was varied between 0.3 and 3 microns/s.</p><p>Upon a 10-fold velocity increase or decrease, gouges of all kaolinite-quartz contents displayed measurable volume change transients. The results show the volume change transients are independent of effective normal stress but are sensitive to gouge kaolinite content. Peak dilation values did not occur in the pure quartz gouges, but rather in gouges containing 10wt% to 20wt% kaolinite. Above a kaolinite content of 10wt% to 20wt%, both dilation and compaction decreased with increasing gouge kaolinite content. At 25MPa effective normal stress, the normalised volume changes decreased from 0.1% to 0.06% at 10wt% to 100wt% kaolinite.  The gouge mechanical behaviour shows that increasing the gouge kaolinite content decreases the gouge frictional strength and promotes more stable sliding, rather than earthquake slip. Increasing the effective normal stress slightly decreases the frictional strength, enhances the chance of earthquake nucleation, and has no discernible effect on the magnitude of the pore volume changes during slip velocity changes.</p><p>Low permeabilities of clay-rich fault gouges, coupled with the observed volume change transients, could produce pore pressure fluctuations up to 10MPa in response to fault slip. This assumes no fluid escape from an isolated fault core. Where the permeability is finite, any pore pressure changes will be mediated by fluid influx into the gouge. Volume change transients could therefore be a significant factor in determining whether fault slip leads to earthquake nucleation or a dampened response, possibly resulting in episodic slow slip in low permeability fault rock volumes.</p>

Seasonal trends of reservoir-triggered seismicity in Song Tranh 2 reservoir, Vietnam

2021 ◽  
Author(s):  
Grzegorz Lizurek ◽  
Konstantinos Leptokaropoulos ◽  
Jan Wiszniowski ◽  
Izabela Nowaczyńska ◽  
Nguyen Van Giang ◽  
...  
Keyword(s):  
Water Level ◽  
Pore Pressure ◽  
Seismic Activity ◽  
Water Level Fluctuations ◽  
Response Type ◽  
Seasonal Trends ◽  
Triggered Seismicity ◽  
Stress Orientation ◽  
Water Level Changes ◽  
Pressure Changes

<p>Reservoir-triggered seismicity (RTS) is the longest known anthropogenic seismicity type. It has the potential to generate seismic events of M6 and bigger. Previous studies of this phenomenon have proved that major events are triggered on preexisting major discontinuities, forced to slip by stress changes induced by water level fluctuations and/or pore-pressure changes in the rock mass in the vicinity of reservoirs. Song Tranh 2 is an artificial water reservoir located in Central Vietnam. Its main goal is back up the water for hydropower plant. High seismic activity has been observed in this area since the reservoir was first filled in 2011. The relation between water level and seismic activity in the Song Tranh area is complex, and the lack of clear correlation between water level and seismic activity has led to the conclusion that ongoing STR2 seismic activity is an example of the delayed response type of RTS. However, the first phase of the activity observed after impoundment has been deemed a rapid response type. In this work, we proved that the seismicity recorded between 2013 and 2016 manifested seasonal trends related to water level changes during wet and dry seasons. The response of activity and its delay with respect to water level changes suggest that the main triggering factor is pore pressure change due to the significant water level changes observed. A stress orientation difference between low and high water periods is also revealed. The findings indicate that water load and related pore pressure changes influence seismic activity and stress orientation in this area.</p><p>This work was partially supported by research project no. 2017/27/B/ST10/01267, funded by the National Science Centre, Poland, under agreement no. UMO-2017/27/B/ST10/01267.</p>

Residual Strength: Does BS 5930 Help or Hinder?

1986 ◽  
Vol 2 (1) ◽  
pp. 279-282 ◽  
Author(s):  
A. B. Hawkins ◽  
K. D. Privett
Keyword(s):  
Stability Analysis ◽  
Normal Stress ◽  
Residual Strength ◽  
Clay Content ◽  
Failure Envelope ◽  
Strength Parameters ◽  
Effective Normal Stress ◽  
Ring Shear ◽  
Stress Dependent ◽  
Shear Box

AbstractBS 5930 offers little assistance to engineers wishing to use residual strength parameters in slope stability analysis. It wrongly suggests the ring shear gives lower parameters than the shear box.BS 5930 does not mention the fact that the residual strength is stress dependent, hence the failure envelope is curved and the parameters must be assessed using an appropriate effective normal stress. For this reason the correlation charts relating ϕ′R to plasticity index or clay content need replacing with a series of charts in which these properties are plotted against ϕ′R values obtained at a number of effective normal stress loadings. Even then such correlations should be treated with caution.

Revisiting the Classical Experiment in Earthquake Control at the Rangely Oil Field, Colorado, 1970, Using a Coupled Flow and Geomechanical Model

2021 ◽  
Author(s):  
Josimar A. Silva ◽  
Hannah Byrne ◽  
Andreas Plesch ◽  
John H. Shaw ◽  
Ruben Juanes
Keyword(s):  
Pore Pressure ◽  
Oil Field ◽  
Coupled Flow ◽  
Injection Wells ◽  
Rock Types ◽  
Pressure Diffusion ◽  
Main Fault ◽  
Injection Interval ◽  
Using Data ◽  
Pressure Changes

ABSTRACT The injection experiment conducted at the Rangely oil field, Colorado, was a pioneering study that showed qualitatively the correlation between reservoir pressure increases and earthquake occurrence. Here, we revisit this field experiment using a mechanistic approach to investigate why and how the earthquakes occurred. Using data collected from decades of field operations, we build a geological model for the Rangely oil field, perform reservoir simulation to history match pore-pressure variations during the experiment, and perform geomechanical simulations to obtain stresses at the main fault, where the earthquakes were sourced. As a viable model, we hypothesize that pressure diffusion occurred through a system of highly permeable fractures, adjacent to the main fault in the field, connecting the injection wells to the area outside of the injection interval where intense seismic activity occurred. We also find that the main fault in the field is characterized by a friction coefficient μ  ≈  0.7—a value that is in good agreement with the classical laboratory estimates conducted by Byerlee for a variety of rock types. Finally, our modeling results suggest that earthquakes outside of the injection interval were released tectonic stresses and thus should be classified as triggered, whereas earthquakes inside the injection interval were driven mostly by anthropogenic pore-pressure changes and thus should be classified as induced.

The role of geomechanical modeling in the measurement and understanding of geophysical data collected during carbon sequestration

2021 ◽  
Vol 40 (6) ◽  
pp. 413-417
Author(s):  
Chunfang Meng ◽  
Michael Fehler
Keyword(s):  
Pore Pressure ◽  
Fault Location ◽  
Mechanical Response ◽  
Fluid Pressure ◽  
Geophysical Data ◽  
Fluid Injection ◽  
Coupled Flow ◽  
Cap Rock ◽  
Stress And Deformation ◽  
Pressure Changes

As fluids are injected into a reservoir, the pore fluid pressure changes in space and time. These changes induce a mechanical response to the reservoir fractures, which in turn induces changes in stress and deformation to the surrounding rock. The changes in stress and associated deformation comprise the geomechanical response of the reservoir to the injection. This response can result in slip along faults and potentially the loss of fluid containment within a reservoir as a result of cap-rock failure. It is important to recognize that the slip along faults does not occur only due to the changes in pore pressure at the fault location; it can also be a response to poroelastic changes in stress located away from the region where pore pressure itself changes. Our goal here is to briefly describe some of the concepts of geomechanics and the coupled flow-geomechanical response of the reservoir to fluid injection. We will illustrate some of the concepts with modeling examples that help build our intuition for understanding and predicting possible responses of reservoirs to injection. It is essential to understand and apply these concepts to properly use geomechanical modeling to design geophysical acquisition geometries and to properly interpret the geophysical data acquired during fluid injection.

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