Failure patterns caused by localized rise in pore‐fluid overpressure and effective strength of rocks

Rozhko, Alexander Y.; Podladchikov, Y. Y.; Renard, François

doi:10.1029/2007gl031696

Cited by 110 publications

(70 citation statements)

References 18 publications

(37 reference statements)

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“…He found that the p-value is 0.48 for an early time period in a sequence of induced secondary aftershocks [71]. This link was also derived by Shapiro et al [72][73][74] and Rozhko et al [75] for the events related to pressure changes in operation wells. Their formulation relates the rate of acoustic events to the temporal change in pore pressure.…”

Section: Discussion Of the Experimental Resultsmentioning

confidence: 75%

Bridging aero-fracture evolution with the characteristics of the acoustic emissions in a porous medium

et al. 2015

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The characterization and understanding of rock deformation processes due to fluid flow is a challenging problem with numerous applications. The signature of this problem can be found in Earth Science and Physics, notably with applications in natural hazard understanding, mitigation or forecast (e.g., earthquakes, landslides with hydrological control, volcanic eruptions), or in industrial applications such as hydraulic-fracturing, steam-assisted gravity drainage, CO 2 sequestration operations or soil remediation. Here, we investigate the link between the visual deformation and the mechanical wave signals generated due to fluid injection into porous medium. In a rectangular Hele-Shaw Cell, side air injection causes burst movement and compaction of grains along with channeling (creation of high permeability channels empty of grains). During the initial compaction and emergence of the main channel, the hydraulic fracturing in the medium generates a large non-impulsive low frequency signal in the frequency range 100 Hz-10 kHz. When the channel network is established, the relaxation of the surrounding medium causes impulsive aftershock-like events, with high frequency (above 10 kHz) acoustic emissions, the rate of which follows an Omori Law. These signals and observations are comparable to seismicity induced by fluid injection. Compared to the data obtained during hydraulic fracturing operations, low frequency seismicity with evolving spectral characteristics have also been observed. An Omori-like decay of microearthquake rates is also often observed after injection shut-in, with a similar exponent p ≈ 0.5 as observed here, where the decay rate of aftershock follows a scaling law dN/dt ∝ (t − t 0 ) −p . The physical basis for this modified Omori law is explained by pore pressure diffusion affecting the stress relaxation.

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Section: Discussion Of the Experimental Resultsmentioning

confidence: 75%

Bridging aero-fracture evolution with the characteristics of the acoustic emissions in a porous medium

et al. 2015

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“…14.6c). The difficulty in quantifying this steady-state is that it is dependent on details of the hydrofracture mechanism (Rozhko et al 2007). An approximation that circumvents this complexity is to assume that the effect of plasticity is to reduce the effective viscosity of rocks undergoing decompaction.…”

Section: Hydrofracture and Decompaction-weakeningmentioning

confidence: 99%

A Hydromechanical Model for Lower Crustal Fluid Flow

Connolly

Podladchikov

2012

Lecture Notes in Earth System Sciences

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Metamorphic devolatilization generates fluids at, or near, lithostatic pressure. These fluids are ultimately expelled by compaction. It is doubtful that fluid generation and compaction operate on the same time scale at low metamorphic grade, even in rocks that are deforming by ductile mechanisms in response to tectonic stress. However, thermally-activated viscous compaction may dominate fluid flow patterns at moderate to high metamorphic grades. Compaction-driven fluid flow organizes into self-propagating domains of fluid-filled porosity that correspond to steady-state wave solutions of the governing equations. The effective rheology for compaction processes in heterogeneous rocks is dictated by the weakest lithology. Geological compaction literature invariably assumes linear viscous mechanisms; but lower crustal rocks may well be characterized by nonlinear (power-law) viscous mechanisms. The steady-state solutions and scales derived here are general with respect to the dependence of the viscous rheology on effective pressure. These solutions are exploited to predict the geometry and properties of the waves as a function of rock rheology and the rate of metamorphic fluid production. In the viscous limit, wavelength is controlled by a hydrodynamic length scale d, which varies inversely with temperature, and/or the rheological length scale for thermal activation of viscous deformation l A , which is on the order of a kilometer. At high temperature, such that d < l A , waves are spherical. With falling temperature, as d ! l A , waves flatten to sill-like structures. If the fluid overpressures associated with viscous wave propagation reach the conditions for plastic failure, then compaction induces channelized fluid flow. The channeling is caused by vertically elongated porosity waves that nucleate with characteristic spacing d. Because d increases with falling temperature, this mechanism is amplified towards the surface. Porosity wave passage is associated with pressure anomalies that generate an oscillatory lateral component to the fluid flux that is comparable to the vertical component. As the vertical component may be orders of magnitude greater than time-averaged metamorphic fluxes, porosity waves are a potentially important agent for metasomatism. The time and spatial scales of these mechanisms depend on the initial state that is perturbed by the metamorphic process. Average fluxes place an upper limit on the spatial scale and a lower limit on the time scale, but the scales are otherwise unbounded. Thus, inversion of natural fluid flow patterns offers the greatest hope for constraining the compaction scales. Porosity waves are a self-localizing mechanism for deformation and fluid flow. In nature these mechanisms are superimposed on patterns induced by far-field stress and pre-existing heterogeneities. IntroductionThe volume change associated with isobaric metamorphic devolatilization is usually positive, consequently devolatilization has a tendency to generate high pressure pore fluids. This generality...

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“…But in order to actually solve the fully coupled grain-fluid deformation, another equation for the evolution of solid grain momentum should be prescribed. In this equation, PP gradients exert forces on the granular matrix [e.g., McNamara et al, 2000], sometimes referred to as seepage forces [Mourgues and Cobbold, 2003;Rozhko et al, 2007]. However, here we first solve a simpler scenario, the infinitely stiff system, which means that the matrix deformation is externally prescribed and the PP only responds to this deformation.…”

Section: Infinite Stiffness Approximationmentioning

confidence: 99%

Pore pressure evolution in deforming granular material: A general formulation and the infinitely stiff approximation

Goren¹,

Aharonov²,

Sparks³

et al. 2010

J. Geophys. Res.

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[1] The physics of deformation of fluid-filled granular media controls many geophysical systems, ranging from shear on geological faults to landslides and soil liquefaction. Its great complexity is rooted in the mechanical coupling between two deforming phases: the solid granular network and the fluid-filled pore network. Often deformation of the granular network leads to pore fluid pressure (PP) changes. If the PP rises enough, the fluid-filled granular media may transition from a stress-supporting grain network to a flowing grain-fluid slurry, with an accompanying catastrophic loss of shear strength. Despite its great importance, the mechanisms and parameters controlling PP evolution by granular shear are not well understood. A formulation describing the general physics of pore fluid response to granular media deformation is developed and used to study simple scenarios that lead to PP changes. We focus on the infinitely stiff end-member scenario, where granular deformation is prescribed, and the PP responds to this deformation. This end-member scenario illustrates the two possible modes of pore fluid pressurization: (1) via rapid fluid flow when fluid drainage is good and (2) via pore volume compaction when drainage is poor. In the former case the rate of deformation controls PP evolution, while in the latter case, fluid compressibility is found to be an important parameter and the amount of pressurization is controlled by the overall compaction. The newly suggested fluid-induced mechanism (mechanism 1) may help explain observations of liquefaction of initially compact soils and shear zones.Citation: Goren, L., E. Aharonov, D. Sparks, and R. Toussaint (2010), Pore pressure evolution in deforming granular material: A general formulation and the infinitely stiff approximation,

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Failure patterns caused by localized rise in pore‐fluid overpressure and effective strength of rocks

Cited by 110 publications

References 18 publications

Bridging aero-fracture evolution with the characteristics of the acoustic emissions in a porous medium

Bridging aero-fracture evolution with the characteristics of the acoustic emissions in a porous medium

A Hydromechanical Model for Lower Crustal Fluid Flow

Pore pressure evolution in deforming granular material: A general formulation and the infinitely stiff approximation

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