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.

The role of elastic, undrained, and drained responses in triggering earthquakes at Monticello Reservoir, South Carolina

1992 ◽  
Vol 82 (4) ◽  
pp. 1867-1888
Author(s):  
Kusala Rajendran ◽  
Pradeep Talwani
Keyword(s):  
South Carolina ◽  
Pore Pressure ◽  
In Situ Stress ◽  
Elastic Response ◽  
Reservoir Induced Seismicity ◽  
Reservoir Impoundment ◽  
Stress Changes ◽  
Individual Contributions ◽  
Monticello Reservoir

Abstract Following reservoir impoundment, stress changes occur due to elastic response and changes in pore pressure due to drained and undrained responses of the substratum. Elastic response may stabilize or destabilize the reservoir environment, depending on the nature of pre-existing stress field. However, the increase in pore pressure always leads to weakening of the rocks, facilitating the onset of seismicity. In most reservoirs, we usually observe the coupled poroelastic effect, and it is usually difficult to isolate individual contributions. Due to the availability of detailed seismicity and geological and in situ stress data at Monticello Reservoir, it was possible to study various factors that control the mechanism of reservoir-induced seismicity. Our results suggest that, during the filling period, the instability resulted from elastic, undrained, and possibly onset of drained response. Subsequently, the seismicity showed a more consistent pattern associated with diffusion of pore pressure.

scholarly journals Analyzing the temporal fluctuations of the reservoir-triggered seismicity observed at Açu (Brazil)

2012 ◽  
Vol 12 (3) ◽  
pp. 805-811 ◽  
Author(s):  
L. Telesca ◽  
A. F. do Nascimento ◽  
F. H. R. Bezerra ◽  
J. M. Ferreira
Keyword(s):  
Pore Pressure ◽  
Time Scales ◽  
Strong Correlation ◽  
Induced Seismicity ◽  
Temporal Fluctuations ◽  
Time Dynamics ◽  
Reservoir Induced Seismicity ◽  
Physical Mechanisms ◽  
Triggered Seismicity ◽  
Pressure Diffusion

Abstract. The time dynamics of the reservoir-induced seismicity observed in Açu area (Brazil) from November 1994 to April 1997 reveals a super-Poissonian behaviour in the direction of a clustering process, where the occurrence of an earthquake increases the likelihood of the occurrence of a subsequent one. The seismicity shows strong correlation for time scales larger than approximately 1 day up to about four months, being characterized by Poissonian behavior for timescales smaller than 1 day. Processes of formation of fractures in the anisotropic and heterogeneous rockmass, along with pore pressure diffusion driven processes, are hypothesized as physical mechanisms for the appearance of Poissonian and clusterized dynamics respectively.

Fluid Initiation of Fracture in Dry and Water Saturated Rocks

2021 ◽  
Author(s):  
Tatiana Kartseva ◽  
Vladimir Smirnov ◽  
Alexander Ponomarev ◽  
Andrey Patonin ◽  
Anna Isaeva ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Induced Seismicity ◽  
Pore Space ◽  
Water Injection ◽  
Fluid Pressure ◽  
Constant Strain Rate ◽  
Confining Pressure ◽  
B Value ◽  
Laboratory Studies ◽  
Uniform Compression

<p>We present the results of the laboratory studies on fluid-initiated fracture in the samples of porous-fractured rocks that have been initially saturated with a pressure-injected fluid and then tested under increasing fluid pressure in saturated rocks. The tests were conducted at the Geophysical observatory “Borok” of Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences. The laboratory is equipped with electrohydraulic press INOVA-1000. The experiments were conducted on the rock samples with substantially different porosity. The tested samples were made of Buffalo sandstones, granites from the well drilled in the area of Koyna-Warna induced seismicity, and of granites from the well in the Voronezh crystalline massif. The permeability of granite samples was varied by their controlled artificial cracking by successive heating and cooling. A preliminarily dried sample was initially subjected to uniaxial loading in uniform compression (confining pressure). Loading was performed at a constant strain rate until the moment when the growth rate of acoustic emission (AE) activity began to accelerate which indicated that the stress level approaches ultimate strength. Since that, the loading rate was decreased by an order of magnitude, and water was infused into a sample from its top face. The bottom end of a sample was tightly sealed and impermeable to water. After this, the pore pressure in the sample that had got saturated with water to that moment was raised in steps whose amplitudes were varied. The obtained results of the laboratory studies show that the character and intensity of fluid initiation of fracture markedly differ under primary fluid injection into the dry porous-fractured samples and under the subsequent increases of the pore pressure in the saturated samples. The time delay of acoustic response relative to fluid initiation and the amplitude of the response proved to be larger in the case of water injection into dry samples than in the case of raising the pore pressure in saturated samples. The theoretical analysis of fluid propagation in a pore space of an air-filled sample in the model with piston-type air displacement has shown that in the case of water injection into a dry sample, the fluid pressure front propagates more slowly than in the saturated sample.</p><p>Investigation of the acoustic activity and GR b-value responses to the cyclic variations of the pore pressure in the fluid saturated rocks was studied in addition. The changes of b-value were found both for increasing and decreasing of the pore pressure. Obtained laboratory results are similar to results from the investigations of the seasonal variations of the induced seismicity in the area of Koyna-Warna water reservoirs.</p><p>The work was supported partly by the mega-grant program of the Russian Federation Ministry of Science and Education under the project no. 14.W03.31.0033 and partly by the Interdisciplinary Scientific and Educational School of Moscow University «Fundamental and Applied Space Research».</p>

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>

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