Flow-through Drying during CO2 Injection into Brine-filled Natural Fractures: A Tale of Effective Normal Stress

Abstract Multiphase fluid flow through rock fractures occurs in many reservoir applications such as geological CO2 storage, Enhanced Geothermal Systems (EGS), nuclear waste disposal, and oil and gas production. However, constitutional relations of capillary pressure versus fluid saturation, particularly considering the change of fracture aperture distributions under various stress conditions, are poorly understood. In this study, we use fracture geometries of naturally-fractured granodiorite cores as input for numerical simulations of two-phase brine displacement by super critical CO2 under various effective normal stress conditions. The aperture fields are first mapped via photogrammetry, and the effective normal stresses are applied by means of a Fast Fourier Transform (FFT)-based convolution numerical method. Throughout the simulations, the capillary pressure is evaluated from the local aperture. Two approaches to obtain the capillary pressure are used for comparison: either directly using the Young-Laplace equation, or the van Genuchten equation fitted from capillary pressure-saturation relations generated using the pore-occupancy model. Analyses of the resulting CO2 injection patterns and the breakthrough times enable investigation of the relationships between the effective normal stress, flow channelling and aperturebased capillary pressures. The obtained results assist the evaluation of two-phase flow through fractures in the context of various subsurface applications.

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Investigation of stresses and normal stress differences behavior on symmetric and asymmetric polymeric fluid flow through planar gradual expansions

Meccanica ◽

10.1007/s11012-016-0531-y ◽

2016 ◽

Vol 52 (8) ◽

pp. 1889-1909 ◽

Cited By ~ 2

Author(s):

M. Norouzi ◽

A. Shahbani Zahiri ◽

M. M. Shahmardan ◽

H. Hassanzadeh ◽

M. Davoodi

Keyword(s):

Fluid Flow ◽

Normal Stress ◽

Polymeric Fluid ◽

Flow Through ◽

Normal Stress Differences

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Residual Strength: Does BS 5930 Help or Hinder?

Geological Society London Engineering Geology Special Publications ◽

10.1144/gsl.1986.002.01.50 ◽

1986 ◽

Vol 2 (1) ◽

pp. 279-282 ◽

Cited By ~ 9

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.

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Two types of reservoir-induced seismicity

Bulletin of the Seismological Society of America ◽

10.1785/bssa0780062025 ◽

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.

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The role of effective normal stress, frictional properties, and convergence rates in characteristics of simulated slow slip events

Geophysical Research Letters ◽

10.1002/2014gl062794 ◽

2015 ◽

Vol 42 (4) ◽

pp. 1061-1067 ◽

Cited By ~ 4

Author(s):

W. David Watkins ◽

Harmony V. Colella ◽

Michael R. Brudzinski ◽

Keith B. Richards-Dinger ◽

James H. Dieterich

Keyword(s):

Normal Stress ◽

Convergence Rates ◽

Slow Slip ◽

Slow Slip Events ◽

Frictional Properties ◽

Effective Normal Stress

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The Recovered Strength of Landslide Soils and its Relation to the Effective Normal stress

Landslides ◽

10.3313/jls1964.37.3_18 ◽

2000 ◽

Vol 37 (3) ◽

pp. 18-24_1 ◽

Cited By ~ 4

Author(s):

Shinya NAKAMURA ◽

Seiichi GIBO

Keyword(s):

Normal Stress ◽

Effective Normal Stress

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Slip-dependent weakening revealed for a shallow megasplay fault in the Nankai subduction zone

10.5194/egusphere-egu2020-5457 ◽

2020 ◽

Author(s):

Alexander Roesner ◽

Matt Ikari ◽

Andre Huepers ◽

Achim Kopf

Keyword(s):

Normal Stress ◽

Constant Velocity ◽

Submarine Landslides ◽

Normal Stresses ◽

Velocity Dependence ◽

Ocean Drilling Program ◽

Coseismic Slip ◽

Megathrust Earthquakes ◽

Effective Normal Stress ◽

Integrated Ocean Drilling Program

The Nankai Trough megasplay fault likely hosts different modes of fault slip, from slow to megathrust earthquakes, and is responsible for related phenomena such as tsunamis and submarine landslides. All types of slip events require some kind of frictional weakening process (e.g. slip and/or velocity weakening) in order to nucleate and propagate. Most frictional earthquake studies analyze the velocity dependence of friction but disregard the slip dependence of friction observed in experimental friction studies.We tested fluid-saturated powdered megasplay fault samples from Integrated Ocean Drilling Program Site C0004 in a direct shear apparatus under effective normal stresses from 2&#160;&#8211;&#160;18&#160;MPa to investigate the velocity- and slip-dependence of friction of the megasplay fault. For every tested effective normal stress, we performed one velocity-step experiment and two constant velocity experiments (no velocity step). In the velocity-step experiments the samples were sheared to a total displacement of 10&#160;mm, with an initial sliding velocity V0&#160;=&#160;0.1&#160;&#181;m/s for the first ~5&#160;mm (run-in) followed by a velocity step increase to V&#160;=&#160;1.0&#160;&#181;m/s over the last 5 mm. During the constant velocity experiments, the shearing velocity (0.1 and 1.0&#160;&#181;m/s respectively) was held constant for 10&#160;mm of displacement.The velocity-stepping tests showed an evolution from velocity weakening at low effective normal stresses to velocity strengthening at high effective normal stresses. All experiments revealed strong slip-weakening behavior, with the slip dependence having a much larger effect on friction than the velocity dependence. The friction slip dependence is also controlled by the effective normal stress, showing large weakening rate at low effective normal stresses and smaller weakening rate at higher effective normal stresses. Therefore, both frictional weakening mechanisms on the megasplay fault become more effective at shallow depths. This may amplify seafloor deformation by shallow coseismic slip and could increase the tsunamigenic potential of the fault zone.

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The hydraulics problem in slope stability analysis

Canadian Geotechnical Journal ◽

10.1139/t91-107 ◽

1991 ◽

Vol 28 (6) ◽

pp. 903-909 ◽

Cited By ~ 4

Author(s):

Étienne J. Windisch

Keyword(s):

Stability Analysis ◽

Slope Stability ◽

Key Words ◽

Normal Stress ◽

Soil Mechanics ◽

Lower Boundary ◽

Slope Stability Analysis ◽

Hydraulic Pressure ◽

Effective Normal Stress ◽

Hydraulic Force

Hydraulic pressures and forces are obtained on a typical slice, as used in current methods of slope stability analysis, under hydrostatic and flowing groundwater conditions. It is shown that current methods do not satisfy some basic hydraulics and soil mechanics principles. The effective normal stress on the lower boundary of a slice is shown to be underestimated, and the resultant hydraulic force is not accounted for adequately. Key words: effective stress, hydraulic pressure, hydraulic gradient, hydraulic force, slope stability.

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Estimating effective normal stress during slow slip events from slip velocities and shear stress variations

Geophysical Research Letters ◽

10.1029/2021gl095690 ◽

2021 ◽

Author(s):

Takuma Kobayashi ◽

Toshinori Sato

Keyword(s):

Shear Stress ◽

Normal Stress ◽

Slow Slip ◽

Slow Slip Events ◽

Effective Normal Stress ◽

Stress Variations

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Frictional slip weakening and shear-enhanced crystallinity in simulated coal fault gouges at subseismic slip rates

10.5194/se-2020-43 ◽

2020 ◽

Author(s):

Caiyuan Fan ◽

Jinfeng Liu ◽

Luuk B. Hunfeld ◽

Christopher J. Spiers

Keyword(s):

Steady State ◽

Normal Stress ◽

Hold Time ◽

Shear Bands ◽

Fluid Pressure ◽

Organic Content ◽

Local Conditions ◽

Frictional Properties ◽

Effective Normal Stress ◽

Fault Gouges

Abstract. Previous studies show that organic-rich fault patches may play an important role in promoting unstable fault slip. However, the frictional properties of rock materials with near 100 % organic content, e.g. coal, and the controlling microscale mechanisms, remain unclear. Here, we report seven velocity stepping (VS) and one slide-hold-slide (SHS) friction experiments performed on simulated fault gouges prepared from bituminous coal, collected from the upper Silesian Basin of Poland. These experiments were performed at 25–45 MPa effective normal stress and 100 °C, employing sliding velocities of 0.1–100 μm s−1, using a conventional triaxial apparatus plus direct shear assembly. All samples showed marked slip weakening behaviour at shear displacements beyond ~ 1–2 mm, from a peak friction coefficient approaching ~ 0.5 to (near) steady state values of ~ 0.3, regardless of effective normal stress or whether vacuum dry flooded with distilled (DI) water at 15 MPa pore fluid pressure. Analysis of both unsheared and sheared samples by means of microstructural observation, micro-area X-ray diffraction (XRD) and Raman spectroscopy suggests that the marked slip weakening behaviour can be attributed to the development of R-, B- and Y- shear bands, with internal shear-enhanced coal crystallinity development. The SHS experiment performed showed a transient peak healing (restrengthening) effect that increased with the logarithm of hold time at a linearized rate of ~ 0.006. We also determined the rate-dependence of steady state friction for all VS samples using a full rate and state friction approach. This showed a transition from velocity strengthening to velocity weakening at slip velocities > 1 μm s−1 in the coal sample under vacuum dry conditions, but at > 10 μm s−1 in coal samples exposed to DI water at 15 MPa pore pressure. This may be controlled by competition between dilatant granular flow and compaction enhanced by presence of water. Together with our previous work on frictional properties of coal-shale mixtures, our results imply that the presence of a weak, coal-dominated patch on faults that cut or smear-out coal seams may promote unstable, seismogenic slip behaviour, though the importance of this in enhancing either induced or natural seismicity depends on local conditions.

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